Systems are made of component parts, and the reliabil­ity of each component part is either known or can be predicted. The reliability of the overall system is what is desired. The reliability of the system can be predicted as a function of the reliabilities of its various component parts by applying the logic of success—failure events in the system.

The methods discussed in this section are “decision tree” logic, Boolean algebra, conditional probability, mini­mal cuts, binomial theorem, and availability analysis All the methods of probabilistic manipulation described here are suitable for hand calculation and some can be used as the basis for computer calculation.

(a) Decision Tree Logic. The “decision tree” is a systematic way of accounting for all the system paths to success and of giving each its proper probabilistic weight. The success diagram of Fig 116 represents a physical

Fig. 11.6—Reliability block diagram for a series—parallel system.

system in which two amplifiers are dependent on one power supply. Success is assured if the power supply and at least one amplifier are operating

The decision tree used to calculate system success is shown in Fig 11.7. Each branch in the diagram, reading

from left to right, represents a decision, go or no-go, on the success or failure of that particular component. By conven­tion, good outcomes branch upward and bad outcomes branch downward. The components are considered in order A good outcome on A and a good outcome on В ensures success, so this branch terminates on the vertical bar labeled “success ” Likewise, a good outcome on A followed by a good outcome on C ensures success. A good outcome on A followed by bad outcomes on both В and C ensures failure. Finally, a bad outcome on A ensures failure regardless of the state of В and C since the amplifiers cannot operate without power

Fig. 11.7 —Decision tree for predicting system success for the series—parallel system of Fig. 11.6.

A probability must be assigned to each branch based on the probability of success and failure of the components in that branch. Assume that the probabilities of success and failure for each component are as follows

Component A Probability of success = 0 999, prob­ability of failure = 0.001.

Component В Probability of success = 0.99, prob­ability of failure = 0.01

Component C Probability of success = 0.99, prob­ability of failure = 0 01

The probability of success may be computed by tracing each success path back to the origin, taking the product of the probabilities along each path and summing the result For success path 1, find the product of (0 99) X (0.999) = 0 98901 For success path 2, find the product of (0 99) X (0.01) X (0 999) = 0.0098901 The total probability of success is the sum of the two products, or 0.9989001.

These rules are essential

1 The sum of the probabilities at each branch must be unity.

2. The components of the system must be considered in order until success or failure is ensured without regard to the state of any of the remaining components

3. The various component-failure events must be statis­tically independent

The least redundant component should always start the first branch and the most redundant components should be considered last to reduce the number of branches on the tree.

The decision tree can handle events with more than two states. It can also accommodate certain physical interdepen­dencies. Consider the success diagram of Fig. 11.8. This figure shows an amplifier driving an output transistor whose

AMPLIFIER TRANSISTOR Fig. 11.8—System with multiple component failure states

output is connected in parallel with the output transistor from another amplifier One amplifier can fail without disturbing the other The output transistor can be good, fail open, or fail short. If it fails short, it voids the output of the parallel output transistor and failure is certain.

The decision tree for Fig. 11.8 is shown in Fig. 11.9. Note that three branches are shown for each output transistor decision good, open, short. Note also that any short causes failure whereas an open only leads to failure in

Fig. 11.9—Decision tree for the system with multiple com­ponent failure states shown in Fig, 11.8.

combination with other failures. As in the previous ex­ample, a probability is assigned to each branch, summing to unity. The probability of success is the sum of the products of probabilities along each success path.

As numerical check, it is advisable to calculate the probability of system failure m the same manner and check to see that the sum of the success and failure probabilities is unity. Such a check does not guarantee against errors in the way the decision nee is branched to represent the problem. Consequently it is essential to exercise care in constructing the tree to be sure that it represents the physical system.

(b) Boolean Algebra. The techniques of using Boolean algebra as an adjunct to probabilistic calculations are documented in many sources.6 8 For those not familiar with Boolean algebra, a simple, but often overlooked, technique will be described.

Consider a two-out-of-three, or majority, logic configu­ration as represented in the success diagram of Fig. 11.10.

Fig. 11.10—Majority logic success model

If any two of the components are good, the system is good. In Boolean algebra, the event “success” is described symbolically as

S = AB + AC + BC (11.3)

where AB means A and В and + means or In words, Eq. 11.3 says, “The system is successful if A and В are good or if A and C are good or if В and C are good.” The negation of A is denoted by the symbol A, which means “not A” or, in this case, “A fails.”

Equation 11.3 can be transformed into a form that is more useful m reliability calculations The following rela­tions from Boolean algebra are used in the transformation

X + Y = X + XY (114)

XY = X + Y = X + XY (115)

XX = X (116)

XX = 0 (11.7)

X = area inside circle (X) = areas b and c Y = area inside circle (Y) = areas c and d X = area outside circle (X) = areas a and d Y = area outside circle (Y) = areas a and b XY = overlap of circles (X) and (Y| = area c X + Y = area covered by circles (X) and (Y) — areas b, c and d XX = overlap of X and X = 0 (since there is no overlap) X + X = area covered by circle (X) and circle (X) = area covered by (X) XX = overlap of X and X = X (since overlap is same as X) X + X = area covered by X and X = total area (a, b, c, and d) = 1 by definition XY = area of overlap of X and Y = area b XY = area of overlap of X and Y = area d X + XY = area covered by X and XY = areas b, c, and d

Fig 11.11—Venn diagram illustrating basic Boolean equa­tions The diagram is a nonrigorous way to visualize the basic Boolean equations. From the above it can be seen that, e. g., XX = 0, YY = 0, X + X = X, Y + Y = Y, X + X = 1,

Y + Y = l, XX = X, YY = Y, and X + XY = X + Y Multi­plying corresponds to “overlapping” or “intersecting”, addi­tion corresponds to “covering” or “union” of the added elements. Multiplication can also be read as “and,” і e, XY = X and Y, addition can be read as “or”, i. e, X + Y = X

Boolean algebra and shows how they may be derived by a graphical representation (the Venn diagram)

Returning to Eq. 11.3, the expression is first broken into two terms

S = AB + [AC + BC]

and then, using Eq. 11.4, this is rewritten as S = AB + AB [AC + BC]

Similarly, the two terms inside the brackets are written according to the form of Eq. 11.4,

S = AB + AB [AC + (AC)(BC)] (118)

From Eq. 115 the terms AB and AC can be written as A + AB and A + AC, respectively. Substituting these into Eq. 11.8 yields

S = AB + (A + AB)[AC + (A + AC) BC]

= AB + AAC + AABC + AACBC + ABAC + ABABC + ABACBC

= AB + ABC + ABC (11.9)

In the final step the relations (from Eqs 11 6 and 11.7) AA = 0, AA = A, CC = 0, and AA = A have been used

In Fig 11.12, the result (Eq. 11.9) is shown graphically. The terms AB, ABC, and ABC are seen to be mutually exclusive, і e, the areas wherein two events intersect are all shown on the Venn diagram, but the areas representing the three terms of Eq. 11.9 do not overlap. Therefore the probability of success is simply the sum of the joint probabilities

P(S) = P(AB) + P(ABC) + P(ABC)

= P(A) P(B) + P(A) P(B) P(C)

+ P(A) P(B) P(C) (1110)

As a numerical example, assume P(A) = P(B) = P(C) = 0.99, then

P(S) = (0.991(0.99) + (0.01)(0 99)(0.99)

+ (0.99)(0.01)(0 99)

= 0.999702

In summary, the foregoing method is as follows

1. Write the Boolean expression that is the union of all possible success paths.

2. Separate the first term and intersect the negation of that term with the rest of the terms Continue down to the last term.

3. Express each negated success path as the union of mutually exclusive events

AB. N = A + AB + . . . ABN

4. Starting with the innermost enclosures, clear the expression using the Boolean relations AA = 0, A + A = A, and AA = A.

5. The probability of success is equal to the sum of the probabilities of the mutually exclusive events

Fig. 11.12—Venn diagram for majority logic case Note that the regions AB, ABC, and ABC are mutually ex­clusive, і e, they do not overlap each other

(c) Conditional Probability Frequently the complex lty of a probabilistic calculation can be reduced by the use of conditional probability It is especially useful if a given component is repeated throughout many branches of the system success model or if the component occupies a key position m the model that makes it difficult to evaluate Conditional probability may be expressed as

P(S) = P(S|A) P(A) + P(S|A) P(A) (11 11)

where P(S) = the probability of system success

P(S|A) = the probability of system success, given that component A is good

P(A) = the probability that component A is good P(S I A) = the probability of system success, given that component A is bad

P(A) = the probability that component A is bad

The method is illustrated by the solution to the reliability model resembling the bridge circuit of Fig 11 13(a) The probability of success can be expressed in the conditional sense as

P(S) = P(S|E) P(E) + P(S|E) P(I) (11 12)

The P(S|E) may be obtained from the easily computed diagram of Fig 11 13(b), where component E is replaced

(a)

(b) P(S|E)

(c) P(S|E)

Fig 11 13—Bridge type reliability model

by a solid line, indicating that E is perfect The P(S|E) may be obtained from Fig 11 13(c), where the path normally provided by component E is missing, indicating that E has failed

This method is described fully in Ref 9

(d) Minimal Cuts A cut is a collection of equipments belonging to a model such that if all these equipments fail, then successful completion of the mission phase repre sented by that model is precluded 10 A minimal cut is a unique set of failed equipment such that the deletion of any one piece of equipment from the cut restores the system to success

Consider the reliability block diagram of Fig 11 14 The hand-calculation method is as follows Start by

Fig 11 14—Reliability block diagram to illustrate minimal cuts method

considering component A as failed and write all the minimal cuts that must include A By inspection, they are AD, AEG, and ABCG Then restore A to operation, and write all the minimal cuts that do not include A In this it is obvious that, for the system to fail, all minimal cuts must either include A or F, thus the remaining paths are FD, and FEG Adding together all the minimal cuts gives an approximate expression for the probability of failure

P(F) ^ AD + AEG + ABCG + FD + FEG (1113)

The approximation is very good provided the probability of failure of each individual component is *^1 For example, if all components have a probability of failure of 0 01, the system probability of failure is 0 000202 by the minimal — cuts method and 0 000201 by an exact method, an error of only 0 05%

In highly redundant systems, not all the minimal cuts need to be written if their total contribution to failure is small compared to the dominant paths For example, if

ABCG is known to be very small compared to AD or FD, ignore it

(e) Binomial Expansion. The bionomial expansion is useful in solving models using redundant components Let p be the probability of success and q the probability of failure of an individual component By definition,

P + q= 1

Likewise,

(p + q)n = 1

where n represents the level of redundancy For example, if n = 5,

(p + q)5 = p5 + 5p4q + 10p3q2 + 10p2q3 + 5pq4 + q5 = 1

The terms represent the various ways success and failure can be achieved The first term, p5, is the probability that all components succeed, there is only one way all of them can succeed The second term, 5p4q, is the probability that four components succeed and one fails, there are five combinations, including exactly four components succeed­ing and one failing There are ten combinations of three successes and two failures, or 10p3q2, etc The terms thus account for all the possible combinations of success and failure of the five components

As an example, consider the system with five relief valves If three or more must function, then the probability of success is

P(S) = p5 + 5p4q+ 10p3 q2

that is, either all five can function, or four function and one fail, or three function and two fail If the probability of a single valve functioning is p = 0 95, then the probability of a single valve failing is q = 0 05 and the probability of system success is

P(S) = (0 95)s + 5(0 95)4 (0 05) + 10(0 95)3 (0 05)2 = 0 9988

In general, the binomial expansion is n

(p + q)n=2(k)pkqnk (1115)

k-0

where

(f) Availability Analysis Senes Subsystems If there are n subsystems in series with failure rates Xi, X2 , X3 , ,

Xn and mean repair times of 0,, 02, $з> > $n and if

repair is instituted on each subsystem as soon as failure occurs, then the series configuration

reduces to

where

Xp — Xj + X2 + + Xn

and

+ X202 "t Xn0n

0T =—————— T—————-

Д-р

The system parameters are

Mean time between failure for the system = (1/Xp) Mean down time for system = 0p

Parallel Subsystems If there are two subsystems in parallel with failure rates X, and X2 and mean repair times 0, and 02, if either one or both subsystems in operation constitute an operating system, and if repair is instituted on each subsystem as soon as failure occurs, then the parallel configuration

reduces to

If there are n subsystems m parallel (partially redundant to each other), each having the same failure rate X and mean repair time в, and r out of n of these subsystems constitute an operating system, and if repair is instituted on each subsystem as soon as failure occurs, then this system

reduces to where

/n — 1 (n-1)’

ir — 1/ (r — l)'(n — r)1

в

n — г + 1

Example 1 Two out-of-three subsystems must operate, ie.,n= 3, r = 2.

Note that the unavailability (= 1 — availability) of the three-out-of-four system is twice that of the two-out-of — three system.

The foregoing relations were derived from Ref 9. In the derivations it is assumed that failure rates and repair times are exponentially distributed and that all в products are <1

By these techniques any simple series-parallel avail­ability model can be reduced to a single block with an equivalent failure rate and repair time. This technique is not applicable to a system with repeated components or components that bridge between series-parallel strings.

In many cases repair does not commence when failure occurs but rather when failure is discovered. This is particularly true of most of the failures of standby systems and of non-fail-safe failures on power-plant protection systems In these cases the mean repair time is equal to one-half the time interval between tests plus the actual repair time.

In the event that repair starts immediately on detection of the failure at a periodic test, the following substitution in the preceding formulas will yield useful results with little error

в* =-+в
2

where в* is a new equivalent repair time including the time elapse between failure and discovery. Frequently the actual repair time is short compared to the time between tests, so the above can be approximated by 0* — г/2

XT = 6X20

в в 1 + 1 2

Availability = 1 — Хт$т = 1 — 3(X0)2

Example 2 Three-out-of-four subsystems must oper­ate, i. e., n = 4, r = 3

(::;b

XT=^ = 12X

в в

1+1 2

Availability = 1 — Х-р^т = 1 — 6(Хб)2

Type of neutron detector BF3 Type of signal cable Triaxial

Location of pulse preamplifier At top of detector instrument well Location of pulse amplifier In amplifier cabinet at control room Distance between pulse amplifier and preamplifier 220 ft Distance between neutron detector and preamplifier 35 ft

Method of grounding A single-point grounding system is used The neutron detector is grounded to the building ground at its point of installation The inner and outer shields of the triaxial cable are grounded at the neutron detector One electrode of the neutron detector is connected to the inner shield The inner shield to the preamplifier is connected to the preamplifier signal ground The outer conductor is insulated and floated above ground back to the amplifier cabinet The signal ground of the preamplifier and amplifier are likewise insulated and floated above building ground, being grounded at the detector Operating problems and modifications During the initial installation and preoperational testing, it was discovered that the start-up channels were excessively noisy, which prevented further operation of the plant These problems were corrected by installing LR filters in the signal lead at the preamplifier output Other noise problems were isolated and corrected at the source, such as faulty switches, relays, and motor starters

See Secs 10 5 5(b) and 10 5 5(c)

(a) Early Coordination Efforts. A typical engineering organization has a development group that is responsible for the design work involved in developing new products If the new product is tied in with a production contract, quality-assurance coordination must be factored into the design cycle as early as possible This can be accomplished by setting up a team of four or five key personnel to review periodically the progress of the design Normally the team would consist of representatives from Marketing, Design, Manufacturing, and Quality Assurance In this way indi­viduals from all the important engineering groups are keyed in to developments on new designs and are in a position to contribute from their special backgrounds They can feed back information to their respective organizations so that timely preparations can be made for manufacturing and testing the new design

Another approach is for the design engineer to hold one or more design reviews, depending on the complexity of the design The participants in the design review normally include the personnel noted above plus any other interested parties The review should be chaired by the design engineer So that the review will be successful, all parties involved must be given all the design particulars (drawings, specifications, prototype test results, design reports, etc ) before the actual review

(b) Design and Performance Specifications. Design and performance specifications must be forwarded to Manufacturing and Quality Assurance as soon as possible so that process development and design and construction of special manufacturing or test equipment may proceed well in advance of the release of the design to Manufacturing For the same reason, design reviews on new products should be held at critical stages of their development, and process reviews should be held on new processes as they are being developed The quality-control engineer should be involved in the development of new processes since it is often possible to integrate test and/or inspection equipment right into the processing equipment, thus ensuring auto matic feedback to keep the process within specification limits

(c) Process Development. The quality-control engi­neer is responsible for ensuring that all manufacturing processes are maintained under control throughout the manufacturing cycle He can best do this by being well informed about all these processes and by keeping in constant contact with the manufacturing engineer The controls he institutes must be consistent with product costs and must be compatible with the associated manufacturing equipment

Two basic types of process control are (1) operator, or open-loop, control, where the operator adjusts the process to keep it under control, and (2) automatic, or closed-loop, control, where the process is regulated by a feedback system. The objective of process control is to keep the process operating within predetermined operating limits

Mechanization of measurements and process control may be accomplished in one or more stages of the manufacturing process, depending on the quality require­ments placed on the product and the process itself For example,

1 Preprocess measurement and control may be required for monitoring or controlling the materials or parts entering the process

2 Measurement and control may be used during proces­sing to regulate the process in response to a measured variable

3 Postprocess measurement and control may be desir­able or necessary if it is difficult or impossible to measure or control the product during the manufacturing process

4 Features of two or more of the above techniques may be combined

(d) Prototype Construction and Testing. During prototype construction and testing, the quality-control engineer may have an opportunity to prove out inspection equipment and in-process testing equipment and proce­dures He should make every effort to have these developed in time to be used and evaluated during the phase

Although prototype testing is normally done by the design engineer, the quality control engineer can assist in these tests and thus gain (1) the product knowledge needed to develop a meaningful quality plan, (2) confidence in the special inspection and testing equipment that has been developed, and (3) the advance information needed to correct the quality information equipment if it does not work satisfactorily on the prototype Prototype testing should subject the prototype to essentially every environ mental extreme in which the unit is intended to operate This may entail use of expensive equipment that may be used for qualification testing alone Even if the test work has to be farmed out, a quality-control engineer should be involved in the prototype testing along with the design engineer so he can become familiar with the new product

Sensor Prototype Testing The major problem with nuclear sensors is that the operating environment of a nuclear reactor is very difficult and expensive to simulate This is particularly the situation for in-core sensors, where meaningful tests (e g, response, burnup rate, saturation level, and signal-to-noise ratio) require accurate simulation Test reactors are available where, by using specially built thimbles and specially designed instrumentation, meaning­ful tests can be performed These should be used whenever possible

Circuit Prototype Testing Circuit designs start with tests of breadboards and subassemblies Each individual module must function within the limits of the environ mental extremes for the complete assembly The design engineer must determine in advance at what stages in the development modules and subassemblies are to be tested to environmental extremes It may be that certain of these tests are only meaningful after the prototype instrument has been completed A test program must be carefully planned in advance so that all necessary tests are performed in a logical sequence and testing facilities are available when needed

System Prototype Testing More and more systems are being standardized, and it has become essential to perform environmental tests, such as temperature rise, on entire systems This can be accomplished by shrouding the entire operating system with a plastic hood and monitoring for hot spots with well-placed thermocouples Appropriate functional tests are performed on prototype systems

Peripheral Equipment Testing Peripheral equipment is normally mechanical and may be subject to wear and fatigue failures due to a hostile environment (heat and nuclear radiation) Life tests must be run to evaluate the reliability of the assembly before proceeding with produc­tion Weld integrity should be checked periodically in these tests

(e) Test Specifications. The results of prototype tests help the design engineer determine the test specifications for the product The test specification should be a formal communication to Quality Assurance which spells out the tests that Engineering believes are essential to prove out the product functionally and the limits of each test Test conditions need to be spelled out to preclude any mis­understanding A description of the test setup should be included

Although Quality Assurance must have the test specifi­cation, this document is not necessarily the only criterion for the determination of test limits on the quality-control test instruction The quality-control engineer may decide to tighten the limits set up by the test specifications if a particular manufacturing process is not as dependable as the quality-control engineer wants it to be or if the measuring capabilities of the test equipment are such that the credibility of the measurement is in doubt For example, as a rule of thumb, the measuring equipment should be capable of reading out to at least ten times the specification limits (This means that if a proportional counter is supposed to be capable of 106 counts/sec, then the count-rate meter must be capable of resolving to 10 7 sec or 100 nsec ) All test equipment, whether being used for engineering prototype tests or for quality control final acceptance tests, must be periodically calibrated to stan­dards that are traceable to the National Bureau of Stan­dards

(f) Engineering-Document Control Since the test specification is an official engineering document, it must be controlled in the same manner as other engineering docu­ments, such as engineering drawings The control of engineering drawings, often referred to as blueprint control, must be accomplished both at the place of origin (by Drafting or Engineering Services) and at the place of use (usually by the Production Control organization)

There are many techniques for maintaining blueprint control These will not be described here However, it should be pointed out that there are pitfalls that Quality Assurance personnel should be aware of Some of these are

1. Advanced manufacturing releases These drawings may or may not be identical with the final release, and any planning that is based on advanced releases must always be contingent on review of the final manufacturing release

2 Marked-up drawings Sometimes it is necessary for the engineer to mark up a drawing prior to the issuance of a formal engineering change There must be some system for maintaining control so that Quality Assurance can be certain the loop is closed One technique is to maintain a log with an open entry that can only be closed when a revised drawing, containing a change identical to that of the marked-up drawing, is issued

3 Engineering changes These should be reviewed by the cognizant quality-control engineer before issuance to ensure that any quality planning affected by the engineer­ing change can be revised accordingly The only effective way this can be handled is to keep the quality-control engineer in series with the engineering change, і e, if his signature is necessary for issuance of any change that may affect (1) health or safety, (2) functional performance, effective use, or operation, (3) interchangeability, reliabil­ity, or maintainability of the item or its repair parts, and (4) weight or appearance (where these are important factors)

(g) Process Instructions Manufacturing process in structions are as important as engineering drawings and must be controlled, і e, Manufacturing Engineering would be responsible for generating such documents, but Engi­neering and Quality Control Engineering must have ap proval authority Any changes to process instructions should be controlled in the same way as engineering changes and should have the same approvals In this way any process-instruction changes that may affect process limits are reviewed to ensure that no product degradation results and that quality checks are appropriately changed

(h) Quality Planning Quality planning is developed throughout the design phase of a new product It consists in determining all the quality checkpoints that are necessary to ensure, with a high degree of confidence, that any rational customer will be satisfied with the product for the duration of its expected lifetime and that the product satisfies all other special requirements, such as applicable standards and codes

Quality planning must take into account software as well as hardware requirements For example, the quality plan must specify the material certification requirements necessary for inspection of raw materials as they are received, the marking and identification of material through its machining and processing, and the in process inspection and tests and documentation thereof, as well as the final acceptance tests and all necessary paperwork required, both internally and for customer submission Thorough quality planning provides for each of the following

1 Determination of control points

2 Classification of characteristics

3 Determination of quality levels

4 Determination of process capabilities

5 Determination of control procedures

6 Appropriate record forms

7 Disposition routines

8 Routing and handling procedures

9 Quality information equipment development

10 QIE calibration

11 QIE maintenance

12 In-process test and inspection

13 Final-product test, inspection, and acceptance

14 In-process audit (both procedure and product)

15 Outgoing product audit

16 Shipping inspection

17 Quality data feedback

18 Quality measurements

A good overall quality system may provide for a general quality plan, an area quality plan, a product quality plan, a contract quality plan, and a vendor quality plan

A general quality plan takes into account quality- control procedures that are common throughout all seg­ments of the business and are followed regardless of what type product is being built or what manufacturing area is involved (e g, quality information equipment calibration)

An area quality plan integrates all the individual station control plans (A station control plan is the basic plan for each identifiable manufacturing station, such as a lathe or an electronic assembly bench This plan is usually an integral part of the manufacturing planning and should include provision for controlling all inputs to the station including direct and indirect materials, e g, stainless steel and cutting fluid or electronic components and solder, tooling, environment, and workmanship skills It should also include provisions for monitoring the station con­tinuously and checking the outgoing part or assembly as necessary ) It includes all controls and procedures that are common throughout a manufacturing area

In an area where there is a definite flow from one station to another, such as an assembly area (as opposed to a machine shop where each article is subject to a different sequence of operations), a flow chart should be constructed to indicate the relations of the various stations to each other and to show every important manufacturing process in its proper sequence with all quality checkpoints inserted Each manufacturing station and quality checkpoint (inspec­tion or test) should be identified by legend and references to the applicable operating instruction or general inspection procedure

In an area where there is no particular flow pattern, a schedule of stations should be established which describes each manufacturing operation or station and all the controls of inputs to such stations as well as specific quality checks applicable to these stations

The area quality plan should describe the environmental conditions required in the area (such as temperature and humidity extremes and cleanliness) and the controls for maintaining such conditions It should describe any special materials handling or in-process storage requirements peculiar to the area And it should describe all quality­measuring tools needed for direct support of production as well as the requirements of the test and inspection equipment for the quality checkpoints in the area Special maintenance work should be delineated for manufacturing tooling, such as stamping dies and cutting tools Calibration cycles on test and inspection equipment in the area should be reviewed and special exception made to the general quality plan whenever there is to be a deviation from standard practice

The quality-data feedback system should be described in the area quality plan and should include applicable quality cost data necessary for analysis, how it is to be obtained, and how it is to be fed back to Quality Control Engineering

A quality training and awareness program is an essential part of a good quality program for each manufacturing area and should provide for both operator training and con tinuous upgrading and verification of quality personnel Every quality plan must provide for an audit that ensures adherence to the quality plan in its entirety

A product quality plan is an integrating plan that ties together the individual quality plans for each of the various assemblies and subassemblies making up the final product and includes all the controls and procedures common throughout the manufacturing cycle of that particular product The product quality plan should reference all applicable area quality plans and workmanship standards as required

The number of individual quality plans for assemblies and subassemblies is dictated by the complexity of the final product, however, each quality plan must contain a flow chart indicating the relation between all lower-tier parts and subassemblies These flow charts should show each impor­tant manufacturing process with all necessary quality checkpoints Each manufacturing station and quality check point (inspection or test) should be identified by legend and referenced to the applicable method sheet or inspection or test procedure The manufacturing-operations sheets and inspection and test procedures should be an integral part of the product quality plan

A contract quality plan is an integrating plan that ties together all applicable area quality plans plus the product quality plan and all special customer requirements resulting from the contract It may modify standard quality plans to the extent necessary to meet all customer requirements The contract quality plan must contain a schedule spelling out in detail the data requirements and identifying who is responsible for them along with a schedule of target dates for each submittal

A vendor quality plan is a plan that describes in detail the requirements of the vendor’s quality system, including any and all requirements for data submittal The vendor quality plan should also spell out the special tests or receiving inspection steps that must be taken to ensure receipt of acceptable vendor material

(i) Process Capability Studies In addition to making certain that the test and inspection equipment is adequate during the prototype stage, the quality control engineer must know whether or not the production equipment is capable of meeting the engineering tolerances and, ac­cordingly, must determine the optimum sampling plan This information can be obtained by performing process capability studies

“Process capability” has been defined as “that which the process is capable of producing under normal, in­control conditions ” The key phrases in this definition are “the process” and “normal, in-control conditions ”

The process includes the entire manufacturing process and all that enters into it, such as the raw material, the machine or equipment, the measuring device, and the skill of the operator or inspector or both The process is a single combination of these factors One process is with a given raw material, a given machine, a certain operator, and the like, whereas another process may be different only in the raw material used Practically speaking, many of the processes made up by these various combinations of factors are similar in output and can be considered as one But only those combinations which will yield the same output under the second condition, “normal and in-control conditions,” can be so considered as one

Normal and in-control conditions are those which yield parts with measurements having a predictable and normal frequency distribution compatible with the target specified Since the process capability is a forecasted distribution of the variability for a given process, this distribution needs to be predictable not only in the spread but also in the shape Generally, most distributions that are not normal indicate a lack of control and nonnormal conditions

Quantitatively, the process capability is defined in terms of six standard deviation units (60) Within ±3a from the mean lie 99 73% of all the readings for a normal distribution For the majority of operations, this 6(7 interval includes practically all the readings and represents the capability of the process Thus, if the process capability is less than the drawing tolerances, a certain amount of sorting and scrap wnl result

The process capability study is a powerful tool Not only can it be computed easily but also its uses are many, including providing the following information

1 To facilitate the design of a product

2 For acceptance of a new or reconditioned piece of equipment

3 For scheduling work to machines

4 For setting up a machine for a production run

5 For establishing control limits for equipment that has a narrow process capability in comparison to the allowable tolerance band

6 For determining the economic nominal around which to operate when the process capability exceeds the toler­ance

The following points should be kept in mind when a process capability study is being performed

1 The study should be taken under normal conditions of operation

2 Factors in the manufacturing process that will introduce nonrandom variations should be held constant

3 Normally, at least 50 readings should be taken

4 The order of the readings should be preserved

5 The individual readings should be plotted over time

6 The measuring devices used should normally have an accuracy of at least 10 times the tolerance spread and 8 times the capability spread

Although computing the process capability from the range is usually the easiest and fastest method, it is also the one that is most affected by the requirement for a normal distribution The first step in computing the process capability through ranges is to compute the ranges, R, of subgroups of the total sample of 50 pieces If, for example, we assume a subgroup of 5, then the average range, R, is the arithmetic average of each of the 10 values of R Using the relation a = R/d2 (where d2 can be determined from the readings, see any standard text on statistical quality control3’4), then we find the process capability is simply 6(R/2 326) = 2 58R for subgroups of 5

Process capability studies can produce savings by identi fying losses due to inadequate processes, poor tool main tenance, unskilled operators, etc The process capability study can help ensure optimum programming of machines and operators in making the product to specification at a minimum cost

10- 5.1 Electrical Noise Problem

Establishing a common ground may be the goal of electrical machinery design, but it creates problems in data measuring systems Ground-loop currents between pieces of equipment that are gounded at separate points to

a common ground introduce voltages that can affect measurements. Differences in potential between various points in a grounding system are not uncommon. These differences are caused by stray currents of any origin m the system, such as faults or transients on electric-power equipment If low-signal-level instrumentation has multiple connections to ground, either bv intention or accident, these potential differences can result in ground-loop cur­rents.

Difficulties attributable to grounding have been experi­enced in several nuclear-power-reactor installations and are difficult to locate For this reason a single-point grounding system is used in nuclear-power-plant reactor instrumenta­tion systems An independent grounding system, isolated from the building grounds, has been installed The concept of an independent grounding system has advantages, how­ever, it will not eliminate capacitive coupling or leakage resistance to ground, which also results in ground-loop currents.

The final design of instrumentation grounding depends on several factors, particularly the types of reactor instru­mentation to be used and the nature of the reactor-building grounding system. Intricate reactor instrumentation sy s­tems almost always require some extensive modifications of grounding connections after the equipment is installed to obtain satisfactory operation

10- 5.2 Grounding System for Reactor Building

The grounding system for a nuclear power station must provide for (1) instrumentation-system grounding, (2) ground connections for grounded neutral power sys­tems, (3) a discharge path for lightning arrestors,

(4) grounding of equipment frames and housings to protect equipment and personnel from dangerous electrical poten­tials caused by faults, and (5) communication and fire — alarm-system grounding

Figure 10.15 shows a system using a grounding grid for a nuclear power station. A properly installed grounding grid with its associated grounding rods or grounding wells should have a total resistance across the entire grid of less than 0.2 ohm. Some nuclear power stations may use means other than a grounding grid for grounding between build­ings, containment spheres, and other major systems. The essential requirement is that all major systems, subsystems, and equipment be thoroughly grounded with ample size grounding conductors and proper grounding connections.

The grounding of a reactor building should be well established All grounding connections to stainless-steel equipment and piping should be made to stainless-steel stringers or saddles welded to the equipment with, if possible, thermite welds Grounding connections should be accessible Two or more grounding connections are recom-

mended for large equipment An equipment ground con­ductor should be included for all power circuits entering the containment. Penetrations of the independent instru­mentation grounding conductors must be insulated from the containment

Purpose To establish a method of identifying raw- material stock in terms of basic composition and thermal condition

Scope This procedure applies to raw metallic material that is to be used for production purposes in the Fabrication Department Specifically excluded are castings and extrusions or any other material that is produced in accordance with engineering drawings and is assigned a part number distinctly different from commercial part numbers

11- A. l Identification System

The identification system used may be expanded to provide for materials that may be added to the listings (Table 11-A.2) by assigning striped colors, which are avail­able within the system, or, if necessary, by using more than a single stripe.

11- A.2 System Description

All metals shall be identified by a color-coding system that uses the twelve basic colors listed in Table 11-A 1 A combination of at least two of these colors is required to identify a stocked item The use of the colors shall be according to the system described in the following para­graphs

(a) Body Color. One of the basic colors is assigned to each of the categories of materials given in Table 11-A 1

Table 11-A 1—Basic Body Colors Color Material category Red Aluminum alloys Blue Magnesium alloys Pink Brasses Yellow Beryllium coppers Orange Bronzes Green Carbon and free-cutting steels Light green Spring steels Aquamarine Alloy steels Brown Stainless steels Gray Magnetic metals Black Cast irons (bars and rods) White Coppers

This identifies the materials as falling within a specific category This color will be the background color or body color over which a stripe will be applied to identify the material according to the categories listed in Table 11-A 2

(b) Body-Color Application

1 Air-dry lacquer shall be used as the body color The colors shall match the stripe tape described below.

2 One end of bars, rods, and shapes shall be painted the body color (see Fig 11-A 1)

3 Sheet and strip and plate stock shall be stacked with one end in the same plane and the entire end painted with the body color

4 Coiled strip, wire, or tubing may be identified per item 3 above by a metal tag painted the body color and attached with a length of wire to the coil [Fig 11-A 1(c)]

(c) Stripe Color Strips of colored pressure-sensitive vinyl tape V8 in wide shall be pressed across the body color painted on the ends of tags, bars, rods, or shapes Painted stripe is used on sheet stock Within any category of Table 11-A 1, the body color shall not be used for a stripe

(d) Stripe Application.

1 The striping tape shall be applied across the center of the body-colored ends of bars, rods, and shapes, except in cases where the diameter is so small or the configuration such that the body color is not clearly evident after the application, then the tape shall be wrapped around the material close to the painted end.

Table 11-A 2—Stripe Colors

Alloy Stripe color	Alloy	Stripe color
	Aluminum	Bronze
1100 0	Blue	Tobin SAL 73	Green
2011 T4	Black	SAI 660
2017 T4	Pink	QQB 691
2024 T4	Yellow	Comp 12	Red
3003 H14	White	MIL N 994
5050 H32	Orange	QQB 636
5052 0	White —orange	SAh 63	Blue
6061 T4	Green	SAE type 1
6061 T6	Gray	class A
6063 T5	Coppertone	MIL В 5687	Pink
7075 T6	Brown
Tool plate	Light green	Carbon and Pree	•Cutting Steel
Brazing sheet White—blue
		В 1113	Red
	Magnesium	1018 (bar and
		rod)	Blue
A731 В	Red	1010 to 1020
A7 31 BO	Pink	(sheet and
A731BM24 Yellow	strip)	White
Tool plate	Orange	MT 1015 (tube)	Yellow
	Brass
QQB 61 3	Red	Magnetic Metal
QQB 626		Hi Mu 80	Red
SAI 72	Blue	Moly —perm	Blue
WW1 791		Mu metal	Yellow
SAI 74	Yellow	Conetie AA	Green
Spring Steel	Cast Iron
1086	Red
		Meehanite	Red
1095	Blue
	Drill Rod	Stainless Steel
Drill rod	Orange	17 7 PH	Red-blue
		301 AN	Red yellow
Alloy Steel	301 I II	Red orangt
52100	Green	3oiV2 и	Red
4140	Red	302 304	Blue
4620	Blue	302 I H	Blue-orange
41 30	Yellow	303S 303SI	Pink
		316A	Yellow pink
Beryllium Copper	321	Light grten
		410	Orange
25A	Red	416	Green
25’/4 H	Blue	430	Gray
25Vjll	Plllk	440A	Light green —
2511	Orange		yellow
10	Green	440C	Yellow
		4401	Gray —yellow
	Copper	Carpenter #10	Blue —yellow
Ol 1IC	Red	МП T 6845
Phosphor	Bron/e Yellow	AST M 269	Blaek

2 Stripes shall be painted over the body color on the ends of sheet, plate, or strip The stripes shall be placed so that when material is cut off a sheet, the color-code identification is not lost

3 Stripes shall be painted on coils of strip, wire, or tubing, or tape shall be applied across metal tags

APPENDIX В QUALITY-CONTROL PANEL INSPECTION CHECKLIST

PROJECT ____________________________ PANEL

INSPECTION DETAILS 1 0 WIRE

1 1 Correct size and type 1 2 Insulation

12 1 Correct type 12 2 Correct color 12 3 Nondefective

2 0 TERMINALS

2 1 Correct type and hole size 2 2 Staking

2 2 1 Full staking impression 2 2 2 Adequate insulation grip 2 3 No damage or distortion to grip or tongue 2 4 Correct wire insertion depth into barrel

2 4 1 Wire insertion is within V, 6 in of

insulation stripback butt

2 5 Use of staking tools approved by the

terminal manufacturer

3 0 CONNECTORS (disconnects or couplings)

3 1 Correct size and type 3 2 Correct clocking

3 3 Insulation sleeving over solder pots (where required)

3 4 Solder pots full of solder (no excessive overflow or peaks)

3 5 Wire insertion in solder pot is within V, 6 in of insulation stripback butt 3 6 Connector shell mated and tight 3 7 Adapter

3 7 1 Tight

3 7 2 Lock washers under screwheads of saddle clamps

3 7 3 Screws tightened evenly 3 7 4 Ground return jumper tight (if used) 3 7 5 Sufficient bushing or number of grommets under saddle straps to secure wires and relieve tension on solder pots

3 7 6 Correct size and type of bushing 3 8 Hi pot test of connectors (where required)

3 9 Potted connectors 3 9 1 Lack of voids 3 9 2 Lack of sponginess 3 9 3 Correct compound type 3 9 4 Correct cure 3 9 5 Proper clearance 3 9 6 Complete fill 3 10 Crimp type pins

3 10 1 Correct staking impression 3 10 2 Correct wire insertion depth into barrel

3 10 3 Insulation stripback is within
V3 2 in of barrel top

3 10 4 Use of staking tools approved by the terminal manufacturer

3 11 Pins properly seated in connector

4 0 CLAMPS (support)

4 1 Correct size (snug fit but not tight)

4 2 Clamp “lip” closed

4 3 Hardware secure 4 4 Cushion closed

4 5 Plastic clamps free of distortion and pulling

4 6 Coaxial cable clamps are free of excessive

tightness to prevent cable distortion

5 0 TERMINAL STRIPS

5 1 Correct size and type

5 2 Terminal lugs are staked back to back (if used in multiple)

5 3 No broken nodes (barriers)

5 4 Terminals are aligned in middle of nodes 5 5 Terminals are correctly and completely identified

5 6 Terminal screwhead slots free from burrs or twists

6 0 COAXIAL CABLES

6 1 Correct type of cable and connector 6 2 Stripping

6 2 1 Inner conductor for correct length, no nicks or cut strands 6 2 2 Shielding and outer insulation for correct length

6 3 Correct assembly sequence 6 4 Contact pin soldered properly 6 5 Location of contact pin is correct after assembly

6 6 Hi-pot or megger test for insulation breakdown (where required)

6 7 Continuity check

7 0 SOLDER

7 1 Identity to type

7 2 Nonuse of acid core solder, fluxes, or paste 7 3 Bonding of wire to connector solder pots or eyelet by solder flow 7 4 No cold solder joints (frosty)

7 5 All wire strands in solder pot or eyelet 7 6 No excessive solder

7 7 No solder spill or splatter into receptacles, devices, components, or printed circuits 7 8 Excessive rosin flux removed 7 9 Soldered connections covered with insulation and secured (where required)

7 10 No overheating of terminals causing insulation scorch, barrier scorch, or component parts burn

7 11 Use of soldering tool with sufficient watt density to ensure acceptable solder joints

7 12 Equipment or hardware mounting to aid

visual identification of part number or value of component after installation

8 0 GROUNDING

8 1 All control shafts and bushings grounded

(unless otherwise specified)

8 2 Ground lugs are utilized in place of parts mounting facilities

8 3 Ground lugs mount on metal surface under screwhead

9 0 SPLICES (when permitted)

9 1 Inspect prior to covering or enclosing into wire bundles

9 2 Correct method and device used to make splice

PANELS, MODULES 10 1 Basic

10 11 Bonding areas clean, free of primers of paint

10 12 Equipment, devices, and operators for correct

10 12 1 Part number 10 12 2 Rating 10 1 2 3 Location 10 12 4 Model 10 1 2 5 Type 10 12 6 Size

10 13 All parts mounted (when prac

tical) so that values and identity are in full view

10 14 Mounting security of parts

10 14 1 Retaining nuts backed up with loc washers 10 14 2 Correct length of screws and bolts

10 14 3 Screwhead slots free from burrs or twists 10 14 4 Bonding areas refinished after installation of jumpers or ground straps 10 1 4 5 Unused mounting or

terminal screws or nuts tightened

10 2 Wire bundles or harnesses secured 10 3 Wire bundles are routed to avoid inter­ference with future terminations, com­ponents, moving mechanical parts, and stub-up locations

10 4 Slack loops are provided where needed to properly facilitate the movement of mechanical moving structures or allow access to components or sub-panel opening or removal

10 5 No twisting or entanglement of wire in harnesses or bundles 10 6 Bushings and barriers installed where required

10 7 Terminals correctly installed and tightened

10 8 Wire breakouts and wire entrances in or out of bundles are consistent Avoid “as the crow flies” or point-to-point wire routing in favor of main wire bundle flow pattern

10 9 Wire terminations at terminal blocks for customer “future tie in” or external con­nections are consistent either to the right or left of the terminal blocks 10 10 All disconnect plugs, receptacles, and con­nectors are suitably covered to prevent entrance of foreign material and moisture 10 11 Correct dimensions of 10 111 Chassis 10 112 Panel fronts 10 113 Mounting hole layout 10 114 Access door 10 115 Clearance requirements 10 12 All wire bundles, harnesses, and wire runs are suitably protected from protruding surfaces, sharp edges, and abrasive surfaces 10 13 Controls 10 13 1 10 13 2 10 13 3 10 13 4 10 13 5 10 13 6

Color

Primer

Dry (air or bake)

Touch-up blended

Free of ripples, sag, orange peel,

over spray, pits, and voids

12 0 METERS

12 1 Correct range 12 2 Scale identification 12 3 Scale and index,

12 4 Size, color, mount

12 4 1 Flush, semiflush, front, back 12 5 Illumination 12 6 Dial or scale background color

12 7 Dial or scale numeral color

13 0 INDICATING LIGHTS

13 1 Illumination factor

13 2 Cover lens color correct

13 3 Engraving correct (where used)

14 0 NAMEPLATES

14 1 Correct etching or attachment 14 2 Drawing number—group number 14 3 Serial number

15 0 WORKMANSHIP

16 0 LAYOUT IDENTIFICATION OF PARTS

17 0 IDENTIFICATION OF COMPLETED

COMPONENTS

18 0 IDENTIFICATION OF PANEL FACILITIES

All controls, indicators, lights, jacks, sockets, and fuse holders marked with suitable words, phrases, or abbreviations indicating the function or use of the part

19 0 IDENTIFICATION OF WIRE TERMINAL

POINTS

20 0 CLEANLINESS

21 0 FINAL INSPECTION

21 1 Compliance to procedure, approved drawings, specifications, and all applicable data

21 2 Cleanliness continuity (if not part of test) 21 3 Function or operation (where required)

21 4 Rework completed and accepted

215 Accessory parts, instruction sheets, or books identified

216 All shortages documented

217 Applicable test and inspection stamps 21 8 Test data complete, reviewed, and

approved

REFERENCES

1 A. V Feigenbaum, Total Quality Control, McGraw-Hill Book Company, Inc., New York, 1969.

2.J. M Juran, Qualtty Control Handbook, McGraw-Hill Book Company, Inc., New York, 1962.

3 E L Grant, Statistical Quality Control, McGraw-Hill Book Company, Inc, New York, 1964.

4 Institute of Electrical and Electronics Engineers, IEEE-STD — 352-1972, General Principles for Reliability Analysts of Nuclear Power Generating Station Protection Systems

5 Benjamin Epstein and Albert Schiff, Improving Availability and Readiness of Field Equipment Through Periodic Inspection, USAEC Report UCRL-50451, Lawrence Radiation Laboratory, July 16, 1968

6 Emanuel Parzen, Modem Probability Theory and Its Apphca tions, John Wiley & Sons, Inc., New York, 1960

7. Montgomery Phister, Logical Design of Digital Computers, John Wiley & Sons, Inc., New York, 1958

8 Norman Roberts, Mathematical Methods in Reliability Engineer­ing, McGraw-Hill Book Company, Inc, New York, 1964

9 Jerome D. Braverman and I Paul Sternberg, Reliability Model­ing with Conditional Probabilistic Logic, Proceedings of the 1966 Annual Symposium on Reliability, sponsored by IEEE, IES, SNT, and ASQC, pp 321-331, Institute of Electrical and Electronics Engineers

10. Stuart A Weisberg and John H Schmidt, Computer Technique for Estimating System Reliability, Proceedings of the 1966 Annual Symposium on Reliability, sponsored by IEEE, IES, SNT, and ASQC, pp. 87-97, Institute of Electrical and Elec­tronics Engineers.

[1]Numerical values used in this section are from Ref 7

[2]A plot of current would vary in a similar way, except that it would not be possible to indicate clearly gas amplification with a steady current

[3]Courtesy Westinghouse Electric Corp t Al2 03 is a high alumina content ceramic

[4]The mean square voltage mode is discussed in detail in Chap 5

[5] Operating Ranges Table З 1 summarizes the oper­

ating characteristics of typical in core fission chambers used

in the pulse-counting mode, the mean square voltage mode,

and the direct current mode Tigure 3 6 shows the upper

and lower boundaries of the operating ranges for in core

[10]From Westinghouse brochure Radiation Detectors Quick Reference Guide November 1967 tThe neutron sensitive material is a breeder mixture of 90% 2 34 U and 10% 2 3 5 U

[11]See L M. Vanderpyl, A Bibliography on Bourdon Tubes and Bourdon Tube Gages, ASME Paper 53 IRD-1, and A. C. Arobone, Strain Gage Transducers for Measurement and Control, Product Engineering Co., Columbus, Ind., 1952.

[12]The sensing of moisture in gas-cooled reactors is covered in Vol. 2, Chap. 18, Sec. 18-3.3.

[13]Gas analysis of the coolant in gas-cooled reactors is discussed in Vol. 2, Chap. 18, Sec. 18-3.3.

[14]See also Vol 2, Chap. 12.

[15]Smce the equivalence of the variance and the mean m certain nuclear radiation measurements was first studied by Campbell [N R. Campbell, Study of Discontinuous Phenomena, Proc Camb Phil. Soc., 15: 117, 310, 513 (1909-1910).], the MSV method is frequently referred to as the “Campbell technique ”

[16]An upper bound to the error. The true error is well below this for highly coherent signals in which statistical effects are minor.

[17]A scram system quickly reduces reactivity, normally by rapid insertion of the control rods The system is usually initiated by a signal or series of signals that indicate an unsafe or potentially unsafe condition (see Chap 12)

[18]From the operating manual for the San Onofre plant.

with boron carbide powder. The 80 control rods enter tne reactor through thimbles in the bottom of the pressure vessel and enter the bottom of the core through holes in the core support plate. A tube for each control rod extends upward from the bottom of the vessel to the bottom core support plate to guide the rods in this region. Each rod is equipped with its own drive mechanism located within the pressure-vessel thimble and operating in the reactor pressure environment.

In most other reactors using vertical control-rod motion, upward rod movement increases the core reactivity by moving the poison section out of and above the core. The Dresden reactor, however, has its control rods fully in

[19]See Vol 2, Chap 14

[20]EIA headquarters are located at 2001 Eye St., N. W., Washing­ton, D. C.

[21]P M. Klein and C Mannal 1 he Effects of High I nergv Gamma Radiation on Dielectric Solids in All / 7ransactions on Lomnmm cations and F lectromcs Part 1 Vol 74, pp 723 731 American Institute of Llectrical Engineers January 1956

*From R В Blodgett and R G I isher, Insulation and Jackets for Control and Power Cables in Thermal Reactor Nuclear Generating Stations, in II El Summer Power Meeting Chicago, Illinois, June 1968, Institute of Hectncal and Hectromcs Fngmeers, New York tDegraded (scission) ^Brittle §Hongated <200%

Note A description of the specific wires tested is given below

[23] PVC Polyvinylchloride per IPCEA S 61-402, Sec 3 8, and UL types TIIW and MT, No 4 AWG (7 strand) copper 0 047 in

wall

2 HD Poly /PVC High density polyethylene, type III, Class В grade 3 per ASTM D1248 63T, and polyvinylchloride per IPCLA S 61-402, Sec 3 7, and IPCIA S 19-81, Sec 4 13 5 No 12 AWG (7 strand) copper, 0 030 in insulation, and 0 015 in jacket

3 SBR/Neoprene Styrene—butadiene synthetic-rubber based insulation per IPCIA S19 81, Sec 3 13 and polychloroprene-based jacket per ASTM D 752 and IPChA S 19-81, Sec 3 13 3, and UL type RHW No 14 AWG (7 strand) copper, 0 047 in insulation and 0 0156 in jacket

4 С В CLP! Low voltage, carbon black-filled, chemically cross linked polyethylene per IPCFA S-66 524, Interim Standard No 2, and UL type RHW-RHH No 14 AWG (7 strand) copper, 0 047 in wall

5 Cl I PUM/Neoprene Ozone resisting mineral-filled bPDM based low-voltage insulation exceeding the requirements of ІРСГА S 19-81, Secs 3 15 and 3 16, and polychloroprene based jacket per ASTM D-752 and IPCLA S-19 81, Sec 4 13, UL type R1IH No 14 AWG (7 strand) copper, 0 047 in insulation, and 0 0156 in jacket

6 Butyl/Neoprene Ozone resisting butyl based insulation per IPCI A S 19-81, Secs 3 15 and 3 16, and polychloroprene based jacket per ASTM D-752 and IPCEA S 19-81, Sec 4 13 3, and UL type RHW RHH No 14 AWG (7 strand) copper 0 047 in insulation and 0 0156 in jacket

7 Oil Base/CSPI Ozone-resisting 90°C oil-base high voltage insulation meeting the requirements of IPCEA S 19 81, Secs 3 14 and 3 15 UL type RHH, and chlorosulfonated polyethylene-(CSPL) based jacket per ASTM D 752 and IPCEA S 19-81, Sec 4 1 3 3, UL type RHH No 14 AWG (7 strand) copper, 0 047 in insulation, and 0 0156-in jacket

8 N I CLPE High-voltage, nonfilled, chemically cross-linked polyethylene (nonstaining antioxidant) per IPCFA S-66 524, Interim Standard No 1 No 14 AWG solid copper, 0 047-m wall

9 C І ГРМ/СРІ Ozone-resisting clay-filled EPM-based high-voltage insulation per IPCLA S-19-81, Sec 3 16, and UL type RHW-RHH and chlorinated polyethylene-based jacket per ASTM D-752 and IPCEA S-19 81, Sec 4 13 3 No 14 AWG solid copper, 0.047-in insulation, and 0 0156-in jacket The insulation was discussed in IEEb paper 31 TP67 481

10 Silicone Ozone resisting silicone rubber insulation per IPCLA S 19 81, Sec 3 17, UL type SA No 14 AWG (7 strand) copper, 0 047-m insulation, and 0 010 in glass braid

11. Neoprene Polychloroprene-based jacket per ASTM D 752 and IPCEA S-19-81, Sec 4 13 3, UL type RHH No 14 AWG solid copper, 0 047-in wall

12 CSPE Chlorosulfonated polyethylene based jacket per ASTM D 752 and IPCEA S 19 81, Sec 4 13 3, UL type RHH No 14 AWG solid copper, 0.047-in wall

13. CPE Chlorinated polyethylene based jacket per ASTM D 752 and IPCEA S 19-81, Sec 4 13 3, No 14 AWG solid copper, 0 047-m wall

[24]See note Table 10.2. tNo test, sample degraded.

[25]1 db = 20 log A, where A is a voltage or current amplitude

ratio.

[26]At the end of Sec. 10-5 5(c), the most widely used and preferred grounding system used in the nuclear industry is de­scribed.

[27]See Chap. 9

[28] К. E. Matick, Transmission Lines for Digital and Communica­tion Networks, McGraw-Hill Book Company, Inc, New York, 1969

4. Portable Wheatstone bridge 4 ranges, 0.1 to 1 to 100 to 1000 ohms, ±0.1% accuracy, and ±0.1% repeatability.

[30] Direct reading pyrometers (one for each range) with 10-in arm, assorted heads, ranges 0 to 400° F and 0 to 1200°F, and ±1% of full scale as millivolt meter

[31] Portable potentiometers (two at least) with assorted scales, such as 32 to 570°F (copper—constantan), 32 to 522°F (iron— constantan), 32 to 1700°F (iron—constantan), 32 to 2425° F (chromel—alumel), 0 to 14 8 mV, 0 to 53 5 mV, and 0 to 155 mV.

3. Portable Kelvin double bridge (for measuring system lead resistances) 8 ranges, 0.0001 to 0.0011 ohm to 2 to 22 ohms, ±0 1% accuracy, and ±0 1% repeatability

[33] Decade resistance box 0 to 1000 ohms in 0.1-ohm steps, ±0.1% accuracy

[34]See also Chap 10.

Type of neutron detector Fission counter Type of signal cable Triaxial

Location of pulse preamplifier Preamplifier cabinet at reactor Location of pulse amplifier Control-room cabinet Distance between pulse amplifier and preamplifier 600 ft Distance between neutron detector and preamplifier 60 ft

Method of grounding The system uses a single-point ground The system is floated above building ground and is grounded to a special instrument ground in a 700-ft deep well A shield around the detector and detector thimble is connected to building ground

(a) Test Instruction Preparation Once prototype testing is completed and the design specifications and drawings are released to Manufacturing, the qualification test program must be developed The prototype testing phase establishes design feasibility and engineering speci fications On the other hand, the qualification testing phase probes whether the product really does meet the engineer­ing specifications when manufactured under normal pro­duction conditions Therefore, the qualification test in­struction must be a comprehensive document covering all the environmental extremes considered necessary to verify product performance

Because some of the tests on such items as in-core sensors are unusual and expensive, the qualification test instruction should be developed jointly by Quality-Control Engineering and Design Engineering In tests of in-core sensors, where the unit being tested may become radio­active or even be destroyed during certain tests, the sequence of tests is vitally important and must be carefully considered It is advisable to perform certain reference tests before and after each environmental test and to perform the most severe tests (such as shock and vibration) near the end of the test phase, thereby accumulating as much reliable data as possible before risking mechanical failure of the product Tests of in-core sensors or other equipment in a neutron flux will render the tested units radioactive, these tests are normally performed last to avoid unnecessary exposure of personnel to nuclear radiation

Prototype testing must be performed under carefully controlled conditions, taking data by automatic means if possible, with well-designed test equipment that is appro­priate for the intended purpose

(b) Pilot Production. The pilot production units must be monitored closely to ensure that quality plans are being followed and are adequate so that the cost of quality does not become exhorbitant Naturally, building the first few production units may involve problems, nevertheless, with sufficient preplanning these problems should be minimized It is advisable to include extra in-process inspections and tests as part of the plan for the first few production units until confidence is built up in production techniques Photographs taken at various critical assembly stages during this stage of production have been found useful, they can be used as samples for future production

(c) Extent of Testing and Equipment Selection One question that never seems to be adequately answered, because of cost and scheduling difficulties, is how many units should be tested If only one unit were to be tested, there would be little confidence in the value of the test results in determining specification limits Assuming a relatively expensive product, three units should be the minimum to be considered for testing However, using the results from tests on 10 units would naturally yield a higher confidence factor, and therefore using 10 units would be preferable

The equipment to be used in qualification testing should be as accurate and reliable as is economically feasible but not necessarily the same as that to be used for production testing Since many of the tests to be performed during the qualification testing phase may be unique, it is not unusual to have special testing equipment designed and built specifically for that purpose

(d) Environmental and Special Functional Tests Nu

clear Sensor Qualification Functional Testing Some of the possible functional tests in qualifying nuclear sensors are

1 Radiographic To observe extremely tight fit up conditions, critical welds, etc

2 Dye penetrant To observe critical welds for possible cracks

3 High potential To observe corona or high-voltage breakdown that may indicate faulty assembly or an incorrect gas fill or improper gas pressure

4 Insulation resistance To determine the integrity of the weld joint and the condition of the insulating surfaces

5 Capacitance To indicate improper assembly or an open circuit in the center conductor

6 Mass spectrometer leak detection To test for seal integrity

7 Partial pressure gas analysis To investigate for gas contamination

8 Pulse-height gas analysis To check on proper gas mixture and pressure in neutron sensors

The choice of the test equipment to check the output of a nuclear sensor depends on what type it is, 1 e, pulse-counting, d-c measuring, or mean-square voltage (see Chaps 2, 3, and 5) If many checks on a quantity of sensors are to be made over any length of time, it will pay to automate the test equipment and have the test data automatically recorded

Nuclear Sensor Qualification Environmental Test ing Environmental tests for nuclear sensor qualification include

1 Gamma sensitivity Up to 107 R/hr, depending on specification requirements

2 Neutron sensitivity Up to 1013 neutrons cm’2 sec’1, depending on specification requirements

3 High temperature Other parameters would normally be tested simultaneously, such as insulation resistance or neutron sensitivity

4 Reactor environment This test should embody as many of the actual environmental conditions as possible

5 Shock This would be required for certain defense applications

6 Vibration The extent would be determined by end-use conditions, e g, in-core sensors should be subjected to vibrations simulating those expected in reactor core

7 Humidity Most out-of-core sensors are in high humidity environments and should therefore be tested accordingly

8 Autoclave This combination steam and high pressure test for in core sensors must be carefully controlled if used

9 Hydrostatic A required test for ASME Boiler Code applications, primarily for testing the integrity of weld joints and sheath

Electronics Instrumentation Qualification Functional Testing

1 Power supply input and output voltage, ripple, line, and load regulation

2 Rise time, linearity, pulse width, waveform, and dynamic range

3 Overall response time with simulated maximum-input cable capacitance

4 Trip-circuit accuracy, hysteresis, and range

5 Calibration checks to specified tolerances at all outputs

6 Full load test for a period of time sufficient to represent a significant fraction of the life expectancy

Electronics Instrumentation Qualification Environ mental Testing

1 High-temperature tests at full load

2 Humidity tests

3. Vibration tests

(e) Error Correction The qualification test program will inevitably indicate that certain design or specification changes should be made Consequently the results should be analyzed promptly and fed back to Engineering for their use in correcting errors in, or improving, the design If the design engineer is performing or participating in the qualification test program, this is unnecessary This is, however, the last good place to make or recommend design changes It may be, for example, that the instrument works satisfactorily but is very difficult to assemble, test, or maintain, thereby indicating the need for a design change

(a) Final-Product Specifications Final-product speci­fications can now be firmed up and released by Engineer­ing This event should trigger a review of all manufacturing and quality-control procedures as well as a review of tools, fixtures, methods, and equipment by Manufacturing and Quality-Control Engineering Hopefully, changes will be minor and any units built during the time of qualification testing will not have to be rebuilt in any way that would necessitate repetition of the qualification tests This deci sion should be made jointly by Design Engineering and Quality-Control Engineering Should it be necessary to repeat some of the qualification tests, the extent of the testing should be considered carefully since normally a complete redesign would be required before a complete rerun of the qualification tests would be necessary

The final-product specifications form a part of the manufacturing release from Engineering which also contains all drawings and parts lists Materials then procures all the various parts in accordance with the specifications

Improper grounding of the electrical switchgear, motor control centers, and machinery has been a source of electrical noise for reactor instrumentation A ground bus with a rating equal to the rating of the largest circuit breaker in the structure should extend throughout the largest of the switchgear assemblies. Each enclosure should be grounded directly to the ground bus The frame of each circuit-breaker unit should be connected to the ground bus through a separate ground contact device except when the primary disconnecting devices are separated a safe distance.

All other equipment requiring ground connections should be connected to the main ground bus by a copper bar or stranded copper cable The terminal fittings should be pressure-type solderless connections. All contact surfaces at splices should be silver-plated. The ground bus should have the same rating throughout the length of the cabinet and switchgear assemblies Tapered ground buses should not be used At each end of the switchgear assembly, cabinets and panels, and motor control centers, provisions should be made for connecting the ground bus to the station grounding system, these connections should consist of silvered sections of the bus

10- 5.4 Grounding of Instrument Panels and Cabinets

Grounding the instrument panels and cabinets does not normally involve the massive amounts of metal required in grounding power systems. Nevertheless, the principles are the same, and all equipment cabinets, racks, etc., must be electrically bonded together and connected to a common ground point These connections should be either welded or bra/ed, particularly the connections to the ground bus from the equipment.

Each instrument-rack structure must be equipped with an electrical grounding bus This bus is generally a 1 25-in. copper bar (Fig. 10.4) mounted in the lower section of the structure. The bus is provided with a means for connecting it to the plant grounding system. Maximum resistance measured from the grounding bus to the building ground should be less than 1 ohm. Where electrical grounding of equipment is required, the structure frame must not be used as a ground path A conductor from the equipment to the ground bus must be provided.

So that electrical noise will not be induced in the instrument circuits, the circuit components must not use the equipment frame ground conductor as a ground. Currents in an equipment ground conductor can cause a voltage drop along the ground conductor, thus changing the point of reference for any circuit using the conductor.

Figure 10.16 shows the grounding system for a series of instrument racks and cabinets scattered throughout the reactor plant, including an instrument panel located in an adjacent building

The independent grounding system for reactor instru­mentation shown in Figs 10 15 and 10.16 terminates at an instrument grounding well and is isolated from the building grounds. The most widely accepted method employs a single-point grounding system for reactor instrumentation that is terminated at one point to the building ground. This latter method provides a ground at the amplifier cabinets in the control room, however, in some nuclear stations the grounding may terminate at the reactor near the neutron detectors.

If an independent grounding system is used, it should be entirely separate from the power grounding system. Several separate areas or zones of instrumentation, divided as to type and location, should be provided with individual grounding buses or conductors that can be connected to the independent grounding system or left floating, as operating experience dictates

An independent ground system requires that all instru­mentation be constructed with the signal grounds insulated from frames, chassis, power-supply grounds, etc. Separation of the two grounding systems involves some difficult practical problems For example, any sensor, amplifier, or other component normally grounded to its housing requires special construction, therefore the type of grounding system used must be decided in advance.

Because of inevitable ground-loop currents over any appreciable length of building ground bus and for added reliability, relays for control circuits should always be operated with one twisted pair of wires per relay. In addition, neither of the relay control wires should be grounded except at the controlling location since to do so may’ introduce circulating currents in the grounded wire as well as m the ground bus.

It is good engineering practice to install suppression devices on control relays to attenuate interference from relay operation. Such devices as diodes, thyristors, or capacitor—resistor networks can be used for this purpose.

Type of neutron detector Fission counter Type of signal cable Coaxial

Location of pulse preamplifier Top of counter tube at reactor Location of pulse amplifier Control room Distance between pulse amplifier and preamplifier 250 ft Distance between neutron detector and preamplifier 50 ft

Method of grounding This system uses a single-point ground at the pulse amplifier The detector and preamplifier chassis are also equipped with r-f paths to building ground at the counter tube Operating problems and modifications After the system was installed, the preamplifier gain was increased to give a better signal-to-noise ratio for the signal between the preamplifier and pulse amplifier A filter was installed in the signal output lead of the preamplifier, this filter eliminated the disturbance on the system caused by the interaction of the ground system in the pulse-amplifier cabinet and the building ground at the counter tubes To protect against any ground loops, the shield on the high-voltage coaxial cable to the preamplifier was lifted from the preamplifier chassis and terminated into a high-valued bleeder resistance Low-pass filters were installed on the power leads to the nuclear instrumentation to eliminate the signal induced by having high — and low-power leads running together

(a) Review and Coding of Material Requests Vendor quality can be controlled by having Quality Engineering review all requests for production materials and parts When the requests are reviewed, several aspects should be kept in mind the estimated cost of the purchased item, the functional criticality of the item, and the relation of the item to the production schedule There should be a quality plan for each purchased part The plan should detail each parameter or characteristic to be checked (and to what statistical plan), should dictate the equipment to be used, and should describe exactly how to perform any tests or inspections other than those considered standard or rou tine

Besides indicating to the vendor the relative importance of the various characteristics of the part, the classification category (see next subsection) gives the quality-control engineer a basis for determining the sample size for his receiving inspection plan For example, he may choose to have every critical parameter or characteristic checked or verified 100% of the time, then perhaps a 0 65% acceptable quality limit (AQL) would be assigned to major charac tenstics, a 4 0% AQL to minor characteristics, and perhaps a one-piece sampling of characteristics that are designated incidental

It is recommended that statistical sampling for attri­butes should be in accordance with MIL-STD-105

(b) Classification of Part Characteristics. A most important step in controlling the quality of the outgoing product is to control the quality of the incoming parts and materials The job of the vendor can be made easier (and therefore better quality assured) by classifying the various characteristics of the part or parts he is to supply If, for example, a part has several dimensions or characteristics, some are obviously going to be more critical to the function of the final product than others Accordingly, typical classifications used are “critical,” “major,” “minor,” and “incidental ” These are usually defined as follows

1 A critical classification means that, should a charac­teristic thus classified not be within specifications, it would likely result in hazardous or unsafe conditions for in­dividuals using, maintaining, or depending on the product or it would be likely to prevent performance of an essential function of a major end item.

2. A major classification means that, should a character­istic thus classified not be within specifications, it would be likely to reduce materially the usability of the unit or product for its intended purpose and would most likely result in a customer complaint

3. A minor classification means that, should a character­istic thus classified not be within specifications, it would not likely reduce materially the usability of the unit or product for its intended purpose but would most likely still be found objectionable by the customer

4 An incidental classification means that, should a characteristic thus classified not be within specifications, it would not be found objectionable except by the most critical customer (e g, a blemish on the inside surface of an instrument housing).

(c) Test and Inspection Equipment Require­ments. The test and inspection equipment needed to support a nuclear instrumentation receiving inspection area includes such items as an insulation-resistance tester (voltage variable to about 1000 volts d-c), an a-c high — potential tester (to about 3500 volts a-c), a helium mass-spectrometer leak detector (sensitive to 10~10 cm3 He/sec), optical comparator (at least 14 in ), dye-penetrant test set, precision bench centers, standard volt-ohm — milliammeter, transistor and capacitor checkers as well as integrated circuit testers, and other electronic component testers

Another possibility to be considered is source inspec­tion, і e., inspecting the product at the vendor’s plant This may be essential in cases where the vendor is either in trouble or is so new that he has not yet proved his ability to produce In other cases, where the cost of the product is very high or the function of the product is critical, the quality-control engineer may consider it important to institute vendor surveillance to ensure that the vendor understands exactly what is required of him.

(d) Material Verification. Whether raw material or completed parts, positive proof of material identity must be on file, particularly in the case of materials and parts for in-core sensors where the ASME Boiler and Pressure Vessel Code applies A practical way to handle this is to have the material certifications reviewed against the applicable speci­fications as soon as they are received If the paperwork is correct, it still may be considered appropriate to make certain chemical spot tests to verify that the material is properly marked or to send a sample to the laboratory for chemical or spectrographic analysis The next step is to file the “certs” by purchase-order number and have the material painted according to an identification system such as that described in Appendix A to this chapter The more critical materials, such as stainless-steel tubing and bar stock intended for use within a reactor, should be marked along their entire length with the purchase-order number, the material identification, and heat number for ready reference at any subsequent time

(e) Destructive Testing Procedures and Use of Labora­tories. If there are any doubts concerning the validity of the certification or if the material requirements are critical, then it is sound practice to send a sample to a qualified materials-analysis laboratory for spectrographic or wet — chemistry analysis Where heat treatment is important, a hardness test should be performed to verify surface condition. Tensile strength would have to be verified by performing a pull test on a tensile specimen

(f) Nondestructive Testing Procedures There are several nondestructive testing procedures available Perhaps the least expensive is the use of a dye penetrant for locating minute cracks (eg, in aluminum insulators and welded tubing). Ultrasonic testing is the best technique for testing large quantities of welded tubing for cracks and flaws, once the equipment is set up, tubing can be tested rapidly Other nondestructive tests, such as radiography, are used more for in-process and final inspection than for receiving inspection

(g) Disposition of Defective Material. Any material found defective by Receiving Inspection, either by test or inspection or as part of a defective lot, should be so identified and segregated from good or unexamined material until it can be returned to the vendor Scheduling constraints may make it necessary to review the nature of the defect and take an alternative action, such as (1) use as is, (2) rework to drawing, (3) rework to an acceptable configuration not to drawing, (4) sort to screen out acceptable parts, (5) scrap, or (6) return to vendor