10- 4.1 Installation Hardware

(a) Conduits. Two basic types of conduit are available, aluminum and steel, other types, such as plastic, are used occasionally. In addition, plastic-coated steel and aluminum are finding wide use where corrosion is a problem. Aluminum is light in weight, free from corrosion by moisture, and easy to install, whereas steel is a far better shield against magnetic fields and has greater strength

Where conduit is to be run through concrete (such as in biological shields), steel should be used since many concrete mixes eventually corrode aluminum, particularly with the presence of moisture If radiation levels and conduit temperatures permit, plastic coated steel conduits yield the best service in damp locations Drain holes should be drilled at low points in exposed conduits to permit any accumu lated moisture to escape, and unexposed conduits, such as shield penetrations, should be arranged so that moisture cannot collect in interior points Conduit should be sized so that the installed wire cables, including allowances for expansion, fill no more than 40% of the conduit area to ensure ease of expansion and repair Information on conduit sizes and available fittings may be found in any equipment manufacturer’s catalog

Particular attention should be paid to joints between aluminum and steel conduit, and, wherever possible, these should be avoided because of the possibility of electrolytic corrosion If such joints must be made, they should be located where they can be easily inspected and protected from moisture

(b) Wiring Trays and Supports. Wiring trays and sup­ports are used wherever it is necessary to route a great number of large-diameter wires to a particular location and still allow easy access to the wiring Solid covered trays are used for instrumentation wiring and open mesh trays for power wiring

Care should be taken that heat buildup in enclosed power-cable trays does not lead to deterioration of insula­tion since power cables in enclosed trays should be operated at a lower rating than those in free air When trays are installed, they should be bonded together to ensure ground continuity and grounding to the main building ground This tan be accomplished by several methods, such as welding and brazing the sections together, using bolted joints, or by running a ground wire along the tray sections and bonding each section to the wire with a suitable clamp (see Sec 10-5).

10- 4.2 Signal and Control Cables

(a) Power-Distribution Cables. Since power cables for instrumentation do not normally carry high currents or high voltages, a reference, such as the latest National Electrical Code (NEC), should be used to determine minimum standards of conductor type, size, etc, and installers should be aware of signal cables in the vicinity of power lines so that proper shielding measures (as shown in Sec 10-5) can be taken. In addition to mterequipment cabling, power lines in mtrarack wiring should be enclosed in wireways wherever possible to improve shielding

(b) Unshielded Control Cables. The present practice in the electrical power industry of standardizing field wires to No 12 or No. 14 AWG with bulky insulation can cause

Table 10 2—Permanent Effect of Gamma Radiation on Physical Strengths of Cable Coverings* H D. C. B. C. K 90° C N F. C. E Sill- Neo- PVC Poly SBR CLPE EPDM Butyl oil base CLPE EPM cone PVC prene CSPE CPE Tensile Strength Original, psi Retention after 2114 2213 1520 2045 1455 798 804 2272 872 1191 2601 2544 2113 2170 irradiation, % 5 x 10s rads 110 96 98 122 104 96 121 102 101 76 80 104 106 112 5 x 106 rads 104 98 100 112 97 58 103 97 106 100 88 98 113 98 5 x 107 rads 79 123 82 101 93 + 98 70 119 100 61 77 124 135 1 x 10s rads 83 118 40 95 79 t 71 59 90 * 200% Modulus Original, psi Retention after 2260 2000 588 1767 1033 520 335 1260 730 859 2415 930 884 626 irradiation, % 5 x 10s rads 94 95 106 125 100 103 121 96 116 75 81 107 116 108 5 x 10[22] [23] rads 90 98 121 115 94 69 126 102 127 112 95 103 156 152 5 x 107 rads § 150 § 120 t 121 108 i? 98 160 203 § 1 X 108 rads § § § § + 103 s? § t Elongation Original % Retention after 260 640 460 270 470 450 870 480 300 290 250 550 560 670 irradiation, % 5 x 10s rads 115 103 93 104 111 93 97 90 96 107 100 96 89 99 5 x 106 rads 115 103 96 96 102 87 90 96 81 90 80 93 86 63 5 x 107 rads 31 70 48 47 + 71 58 41 34 40 46 59 18 1 x 10’ rads 19 2 33 37 32 t 53 25 26 t t

Table 10.3—Permanent Effect of Gamma Radiation on Dielectric Constant (k’) of Cable Coverings’^ Dose, rads Measured after 2 hr, °С PVC H. D. Poly. SBR C. B. CLPE C. F. EPDM Butyl 90° C oil base N. F. CLPE C. F. EPM Silicone k’ (S. I.C.) , 40 volts/mil, 60 Hz None 23 4.90 2.58 3.32 3.58 3.37 4.35 3.44 2.25 3.47 3.11 75 6.82 2.52 3.84 3.44 3.19 4.21 3.27 2.30 3.49 2.96 90 7.32 2.51 t 3.04 3.18 4.14 3.09 2.30 3.44 2.98 % Change 5 x 10s 23 + 3 -1 +5 -1 -4 -2 +5 +7 +8 0 75 -4 -2 + 10 -2 -4 -2 0 + 3 0 -i 90 +52 + 1 t +4 +5 -2 +2 -4 + 3 -i 5 x 106 23 +4 + 39 +5 + 3 -9 -20 + 10 + 3 +8 +29 75 +6 +42 +6 -7 -6 0 -4 -7 + 3 -8 90 t + 132 t +4 +5 0 + 3 +4 + 3 -8 5 x 10’ 23 +21 + 36 + 1 + 3 -7 -20 +6 + 3 + 10 +2 75 +41 + 39 -9 -1 -8 § + 1 -1 +6 + 1 90 t + 104 t +9 +2 § + 10 +9 +9 0 1 x 108 23 +59 -6 + 1 +2 + 1 § + 7 +2 +7 +6

*See note Table 10.2.

tThe high dielectric constants of the neoprene-, CSPE-, and CPE-based jacket materials were not significantly affected.

$Loss higher than limit of bridge.

§No test, sample degraded. [24]

Table 10.4—Permanent Effect of Gamma Radiation on d-c Resistivity of Cable Coverings* Dose, rads Measured after 2 hr, °С PVC H. D. Poly. SBR C. B. CLPE C. F. EPDM Butyl 90° C oil base N. F. CLPE C. F. EPM Sili­ cone Neo­ prene CSPE CPE D-C Resistivity, 100 Teraohms-cm, 500 volts D -c None 23 0.15 240 2.3 70 12 76 15 141 71 0.2 10~3 0.2 10“2 75 10"4 25 10~3 40 0.3 0.2 1.2 68 1.3 10~2 10"4 1 0-3 1 0 /4 90 10 4 20 10 4 37 0.3 0.1 0.1 50 1.0 10"3 10~6 10 4 10’3 % Change 5 x 10s 23 -28 m 1 +50 + 33 -20 0 -i -4 + 11 +57 -31 -14 -46 75 -90 -32 +48 +50 + 32 -14 + 100 -3 + 10 0 -34 -32 -55 90 -23 -90 -6 -33 -29 -51 + 100 -3 0 +52 -85 -54 + 198 5 x 106 23 -48 -70 + 13 -59 -4 0 -1 -4 + 38 0 + 15 -5 0 75 + 10 -99 +40 + 17 -8 -84 +66 -3 -9 +25 +4 -17 0 90 -47 -92 0 -43 -51 -98 +90 -3 0 +15 +415 -82 + 19 5 x 107 23 -67 -81 +48 -68 +5 3 -82 -5 -4 +25 +60 0 0 -14 75 + 100 -80 +250 -52 -34 t + 33 -4 -7 +20 + 11 -17 -92 90 +27 -99 + 100 -75 -79 + +25 -3 -40 +64 + 390 -75 -85 1 x 108 23 + 120 -70 +58 -7 +60 t + 35 -8 0 +60

Table 10.5—Permanent Effect of Gamma Radiation on Flame Resistance
of Thin-Wall Wires in Underwriters Laboratories Flame Test*+

H. D. C. F. 90° C C. F.

Poly./ SBR/ C. B. EPDM/ Butyl/ oil base/ N. F. ЕРМ/ Silicone

PVC PVC neoprene CLPE neoprene neoprene CSPE CLPE CPE glass

Dose, rads	0	10s	0	10®	0	10s	0	10s	0	108	0	10s	0	10s	0	108	0	108	0	108
Results	p	p	F	P	F	F	F	F	p	p	F	F	P	p	F	F	P	P	p	p
% flag destroyed	0	0	100	0	100	100	100	100	0	0	100	20	0	0	100	100	0	0	0	0
After burn, sec	0	0	180	0	52	60	180	100	0	0	50	80	0	0	180	180	0	0	0	0

*See note Table 10 2 tP, pass, F, failure

Table 10.6—Threshold (in rads) of Gamma Radiation Damage for Elastomer-Based Cable Coverings*

H. D. C. B. C. F. 90° C N. F. C. F. Sili — Neo­Property PVC Poly SBR CLPE EPDM Butyl oil base CLPE EPM cone PVC prene CSPE CPE

Tensile strength

108

108

5 x 107

108

108

5 X 106

10s

5 x 107

108

5 X 107

5 x 107

5 x 107

5 x 107

5 x 10

Elongation

5 x 107

5 x 106

5 x 107

5 x 107

5 x 107

5 X 106

108

5 x 107

5 x 107

5 X 107

5 x 107

5 x 107

5 x 107

5 x 10′

Rate of oxidation

5 x 106

>5 x 107

>5 x 107

>5 x 107

5 x 106

>5 x 107

5 x 106

5 x 107

5 x 105

5 x 106

5 x 106

5 x 107

5 x 10′

Dielectric loss

5 x 107

5 x 10s

108

108

108

5 x 106

108

5 x 105

108

108

5 x 107

5 x 107

5 x 107

5 x 10

Electric stability

5 x 10s

>5 x 107

5 x 10s

>5 x 107

5 x 107

5 x 10s

5 x 107

5 x 107

>5 x 107

>5 x 107

5 x 105

5 x 10s

5 x 106

5 x 10′

Dielectric strength

5 x 107

5 x 107

5 x 107

108

CO О Л

5 x 106

108

>106

>108

>108

5 x 107

5 x 10s

5 x 10s

5 x 10

Overall threshold of damage

5 x 105

5 x 106

5 x 105

5 x 107

5 x 107

5 x 106

5 x 107

5 x 106

5 x 107

5 x 105

5 x 105

5 x 106

5 x 106

5 x 10′

Highest dose still serviceable

5 x 10‘

5 x 107

5 x 107

108

108

5 x 106

108

108

108

5 x 107

5 x 106

5 x 106

5 x 107

5 x 10

*See note Table 10.2.

Table 10.7—Suggested IEEE Nuclear Environment Classification for Elastomer-Based Cable Coverings Temperature Class Radiation class O(90°C) A(105°C) B(130°C) 1 (9 x 104 rads) Silicone (see Note 1) Silicone (see Note 1) Silicone 2 (9 x 10s rads) Butyl/neoprene, CSPE, CPE, and H D Poly See below None 3 (8 8 x 10s rads) EPDM, EPM, oil base, N. F CLPE, and С В CLPE EPDM, С В CLPE, and EPM None 4 (8 8 x 109 rads) None None None 5 (101 0 rads) None None None

Notes

1 Dimethylsihcone based insulations (IPCEA S-19 81, Par 3 17) are suitable at their usual 130°C temperature rating only in low-radiation environments because of their sensitivity to steam and poor resistance to oxidation after irradiation Blodgett and Fisher rate them only in classes Ol, Al, and B1

2 Carbon-black (and probably clay-filled) cross-linked polyethylenes and clay-filled EPM — or EPDM based insulations are suitable at 105°C up to class 3 radiation levels when protected with suitable flame-resistant braids (such as the glass construction used in Blodgett and Fisher’s study) or flame and water-resistant asbestos constructions Blodgett and Fisher rate these two materials for classes Ol, 02, 03, and Al, A2, and A3

3 Butyl and high-density polyethylenes with neoprene, CSPE, or CPE jackets or the CPE as integral insulation jackets are suitable at their usual 90°C temperature rating only up to class 2 radiation levels Blodgett and Fisher rate these systems only for classes Ol and 02

4 Nonfilled cross linked polyethylenes and oil-base insulations, when protected by a neoprene, CSPE, or COE jacket, are suitable at their usual 90°C temperature rating up to class 03 Blodgett and Fisher rate these systems for classes Ol, 02, and 03

5 SBR and PVC-based coverings are suitable only at relatively low temperatures and radiation levels In particular (IPCEA S 61-402, paragraphs 3 7 and 3 8), PVC’s are sensitive to hot water and steam when exposed to more than 5 x 105 rads

serious installation problems if the instrument-cabinet terminal blocks are not properly sized The design engineer and instrument-cabinet manufacturer should allow ample space m the cabinet for terminal blocks, conduits, and wireways to accommodate the large-size field wires Single­conductor field wires with diameters of % to ^16 in are being used m power-station design

Several types of single conductor wire with small- diameter plastic insulation are durable and meet all the environmental requirements for power-station design

Where smaller (No 18 to No. 22 AWG) wires are used, they should normally be in the form of cables having a number of twisted pairs covered by an outer sheath, with one pair assigned to each circuit function Avoid having several circuits tied to a single ground conductor since, if this conductor fails, a number of circuits will be put out of commission instead of only one

It is evident that only power cables, switch commands, relay operating signals, and lines that can tolerate some cross-talk, such as communication lines, should be run m unshielded cables

If one of these lines is terminated in a terminal strip or block, solderless crimp connectors may be used, if the line terminates in a connector, solderless or solder-type termina­tions may be used. When wires are terminated in a connector, covering each wire with teflon tubing, shrink tubing, or other insulation will decrease the probability of shorts

In general, unshielded wiring is much easier to install than shielded and, if standards such as those referenced in other sections of this chapter are followed, should create no problems

(c) Instrument Signal Cables (Multiconductor, Shielded). Because of cross talk, spike induction, and other interference problems, it is important to consider the routing of each cable with respect to its electromagnetic environment Mixing of low-level signals, relay command’ servomotor control currents, and communication cables m the same conduit or raceway results in interference problems whether shielded cable is used or not Good practice dictates that instrumentation cables be separated physically according to signal level and function as well as electrically by shielding etc, wherever possible In critical circuits, such as reactor-control circuits, separate each channel’s measurement and control function from all others This will result m at least three sets of separately run conduit, color coded or identified in some way If this policy of separation is followed along with coincidence safety logic in the control-instrumentation design as well as in wiring layout, any portion of the control system may be disconnected without causing a scram

Isolate wiring according to function Cables carrying high currents or voltages should be isolated from those carrying low currents or voltages, and cables carrying interference-producing signals should be isolated from those carrying direct current A designer should use a separate

Table 10.8—Installation Symbols Commonly Used in the Nuclear Power Industry

© ©"

Winding connection З-phase ungrounded Winding connection З-phase grounded Piping

Resistor Capacitor Battery Alternating-current source

©

1———— і

Primary flow line

f-

■i

Secondary flow line

<

Thermocouple

ASMF Boiler Code line Control air line Instrument capillary tubing Flexible hose Valves Gate Globe Check Stop check Plug Angle Manual flow controller

Thermal element Conductor and junction 2-conductor cable Shielded 2-conductor cable Coaxial cable Ground Basic contact assemblies Electromagnetic actuator with mechanical linkage Push-button switch Coaxial connector Transformer Fuse

©

)—- l^Cj—!

olo

MO©

UUUUU

nnnnn ronnn AIR CORE IRON CORE

*—

Butterfly Relief

Circuit breaker

Semiconductor rectifier diode

© © © ©

Electromatic relief

Meter

Three-way

Rotating generator

Four-way

Rotating motor Winding connection 1-phase

О

Throttle

Table 10 8— -(Continued) Bleeder trip Local mounted transducer electric to pneumatic Locked open 10 —CX—’ Amplifier controller Locked closed L C —ж—• Miscellaneous Instruments Self contained Flow meter Control (opens on air failure) I Ob T Sight flow indicator Control (closes on air failure) —i? i—« In line flow indicator Air lock AL Л -Ль- Flow nozzle Operators Flow orifice Diaphragm -Ль- Restricting orifice /lJov Electric motor -Ль- /povN Thermocouple Nonelectric power Resistance bulb -ЬКЬ- Float —Ы<н Sample cooler Manual trip and reset -Ль- 1 /sv Sample nozzle Solenoid —Л— Drain trap Damper with electric operator і i T® u Manometer Damper with air operator Basket strainer Instruments Local mounted 00 Hose connection Panel mounted | PI | PS | Air relay ^-BOARD Annunciator alarm Н00ХХ SYMBOL N/ Remote manual control Local mounted transducer Air switch pneumatic to electric

AC

conduit for all low-level (detector, thermocouple, etc.) signals, a separate conduit for high-level control signals containing shielded wires, a separate conduit for relay and contact closure leads, and a separate conduit for a-c and d-c power distribution.

If every precaution is not followed, scrams mav be caused by arc welders or other noise-producing devices, such as switching d-c circuits, when placed near the detector cables.

Concerning the signal and control cables, each cable should carry only signals of the same type and, for instrumentation purposes, should have at least an overall shield (either braid or metal foil) for each group of conductors In all instances the cable shielding should have an insulating layer over the shield to provide isolation from ground-loop currents likely to be circulating in the outer conduit. Each of the two most common types of shields (braided and foil) offers different degrees of shielding protection. The braided type of shield offers good protec­tion for low-level signals. However, because of the effect of leakage capacity through the braided shield to ground, common-mode reflection suffers, and something better is needed for noise-free transmission of microvolt-level signals. Lapped foil shields have been developed for this purpose, and this type of solid-foil shield, plus a low-resistance drain wire, reduces the leakage capacity from about 0.1 to 0 01 pF/ft, typically. In addition, the foil shield improves shield-to-ground electrical leakage characteristics, rejection of magnetic pickup, and shield-resistance characteristics, and reduces termination problems

Conductor pairs within the cable should be of the twisted variety since this in itself reduces interference as much as 15 dB [25] The use of balanced, twisted pairs is even more effective, resulting in an interference reduction of up to 80 dB. The foregoing techniques were applied in the construction of the Ballistic Missile Early Warning System (BMEWS), where many different types of cables were located in close proximity to one another. In this system inherent shielding of the cableways provided 6-dB attenua­tion, twisting of power and other cables provided 26 dB, and the use of balanced, twisted pairs added another 80 dB

Because instrumentation cables must not be considered separately from the system in which they are to be used, the designer should consider terminating all cables carry ing signals having frequencies greater than 10 kHz with their characteristic impedance to avoid end reflection. Termina­tion of signal cables depends on the type of cable and the signal levels involved. In general, cables other than coaxial can be terminated using color-coded crimp connectors of the “ring” type and affixed to terminal strips Each end of a conductor should also be marked by attaching a piece of plastic sleeving bearing the wire designation number as shown on the system interconnection diagram.

Wires within a conduit should not exceed code limits to ensure easy cable pulling. No splices should be allowed except in appropriate junction boxes [see Sec 10-4.1(a)] . The conduit “fill” should not exceed 40%, including planned additional space reserved for system changes. When cable is pulled through conduit, excessive stress should not be placed on the cables since this may result in damage to insulation in regular wiring or changes of impedance in coaxial cables. Spare conductors should be installed in each cable to permit system expansion. As a rule, running 10 to 15% more conductors than required seems to work well 1 his allows for additions without raising the cost exces­sively. However, the type of reactor installation (power, experimental, etc.) may alter this general rule.

Termination of thermocouple leads is a special case, and the manufacturer’s instructions should be followed to ensure that there are no error currents produced by improper terminations In addition, thermocouples should be kept away from cables carrying high current or voltage signal levels Self-balancing temperature recorders respond too slowly to be affected by transients on thermocouple leads. However, electronic time-sequential multiplexing of large numbers of thermocouples into a device (such as a computer) requires that transients on the thermocouple leads be eliminated since sampling of a particular thermo­couple may occur when the signal level is being influenced bv a transient.

(d) Coaxial and Triaxial Cables. Coaxial and triaxial cables require care in selection and termination because signal levels are of the order of 1 mV or less Triaxial cables provide additional low-frequency’ (<100 kHz) shielding attenuation of 20 to 40 dB over coaxial cables, and additional benefits, such as low leakage, may be gained by appropriately driving the inner shield as explained in Sec. 10-5.5(a) Regarding installation of these cables, it is safe to use BNC type connectors of either the crimp or solder style up to 500 volts d-c. (The crimp type is popular.) Above 500 volts d-c, MI1V series connectors may be used to voltages of 5000 volts d-c, except where high-frequency pulses are present At very high pulse rates (>1 MHz), the connector impedance must match the cable, and so other types of connectors must be chosen. When cable connectors are being installed, care must be used to ensure that there are no loose ends of the shield braid to cause shorts or lower the breakdown resistance of the connector After the cable has been assembled, the test procedure outlined in Table 10.9 is recommended

Table 10.9—Cable-Testing Procedure Operating voltage Test procedure <600 volts d l 2 times rated voltage plus 1000 volts applied for 1 min. >600 volts d-c 2 25 times rated voltage plus 2000 volts applied for 1 min

Since magnetic and electric fields are responsible for most interference problems below approximately З МН/, low-frequency (60 II/) pickup should be guarded against b using steel conduit around low-level coaxial and triaxial cables The steel effectively attenuates both magnetic and electrostatic fields at all frequencies

At termination ends of coaxial or triaxial cables, each connector should be marked with its appropriate print number as well as the number of the mating connector for the particular cable An appropriate marking device is a plastic sleeve wrapped around the cable end and bearing the necessary information

When triaxial cable is used, connector assembly is more critical than when BNC is used, and greater care must be taken m testing the completed cable The tests in I able 10 9 should be applied in this case not only between center conductor and inner shield but also between the inner and the outer shield to ensure proper connector integrity I or extra protection a quantity of silicone grease — may be used inside the connector to provide additional insulation and to prevent accumulation of moisture within the connector

(e) Containment Penetrations. Penetrations for signal, control, and power tables m the leactor containment have been custom designed Custom designed penetrations, in many cases, required assembly at installation and disassem bly for repair Man) problems experienced with contain ment penetrations resulted from field-assembly conditions Although the problems experienced yvith field-assembled penetrations were often similar (e g, difficult installation, leaking seals, and poor wire termination), the variety of
custom designs prevented universal solutions from being applied to similar problems

I or greater reliability and ease of installation, several manufacturers have designed and now fabricate preasscmbled and pretested electrical penetrations These penetrations can be supplied with seals that are compatible with a variety of ambient environmental conditions (tem­perature, moisture, and nuclear-radiation level) Penetra­tions can be supplied with electrical conductors ranging from unshielded control and power wires to coaxial, triaxial, and other types of shielded cable Wire termina­tions are ayailable that range from pigtails and pressure or crimp splice tubes to special high-voltage and shielded connectors 1 he preassembled penetrations are tested at the factory for leak rate, conductor continuity, and insulation resistance The assembled and tested penetrations can be equipped with a leak-monitor pressure gauge and pressur i7ed with inert gas, thus allowing the penetration to be monitored for leaks during shipment and installation as w’ell as during operation. The preassembled penetration can be supplied for field installation with a welding ring or a bolted flange Pigure 10 14 shows some of the features available in preassembled penetrations