The final portion of the meeting concentrated on developing issues associated with non-piping contributions (passive failures only) to the LOCA frequencies. Active components will be analyzed separately during this program from operating experience. Because active components have maintenance

plans, the group in general expects that the failure rate of these components will not increase in the future. Operating experience should therefore adequately represent active component failure rates. This rationale is the basis for considering only passive component failures within this elicitation.

The non-piping contributions will be combined with the piping component to determine the total LOCA frequency (Figure B.1.1). The group decided to break these issues down by component functionality.

This is an analogous approach used to tackle the piping contribution which initially segregated piping systems by functionality. Five main components were determined as candidates for passive failures: the pressurizer, the RPV, valves, pumps, and steam generators/steam systems. The valve component category encompasses both pressure isolation valves at Class 1 to Class 2 piping boundaries and also loop-stop valves. The pumps category only considers pumps in the reactor coolant or recirculating water system.

For each component category, the panel developed sub-categories which represent specific possible failure modes (e. g. what portions of the component could fail passively). Each failure mode is governed by the same variables that are important for piping systems (material, geometry, loading, degradation mechanisms, and mitigation/maintenance). Unfortunately the group did not have sufficient time or resources to fully develop comprehensive variable lists in the same manner as for piping systems.

Table B.1.13 illustrates the failure modes developed for pressurizer failures. Please note that all table abbreviations for this and all subsequent tables in this section are as previously defined unless indicated. Bold items in the failure mode sub-category of Table B.1.13 (and all following tables) indicates that operational data exists which captures that component failure. For instance, in Table B.1.13, the group thinks that data is available on heater sleeve failures.

Table B.1.13 Pressurizer Failure Scenarios

Component	Geometry	Material	Degradation Mechanisms	Loading	Mitigation/ Maintenance	Comment
Shell		A600C-LAS, SSC-LAS	GC, SCC, MF, FDR, UA			Boric acid wastage from OD
Manway		NB-LAS, SSC-LAS, LAS, HS-LAS (Bolts)	GC, SCC, MF, SR, FDR, UA			Bolt failures
Heater Sleeves	Small diam. (3/4 to 1 in)	A600, SS	TF, MF, SCC, FDR, UA			Req. multiple failures
Bolted relief valves		C-SS	MA, FDR, UA
Nozzles		SSC-LAS C-SS	CD, TF, SCC, MA, FDR, UA, GC			Same as surge line

NB-LAS = nickel-based clad low alloy steel SR = Stress Relaxation and loss of preload

The panel identified failures in the pressurizer shell, manway, heater sleeves and nozzles as passive LOCA candidates. Also, the pressurizer bolted relief valves could fail. The group generally did not have information on component geometries and loading and mitigation/maintenance were not discussed by the panel due to lack of time. However, some specific issues were discussed for each of these failure modes. The shell failure envisioned would most likely occur by boric acid wastage from the outer diameter of the

shell. Manway failures would result by multiple bolt failures. Heater sleeves fail due to PWSCC, but as a result of their size, multiple failures are required in order to result in a LOCA. Bolted relief valves could fail due to steam cutting or localized bolt corrosion resulting from boric acid leaks.

The RPV failure modes (Table B.1.14) focused on vessel head bolt failure, failure of CRDM connections, nozzle failure, RPV wastage, and RPV corrosion fatigue. Upper head vessel head bolt failure is most likely due to human error during removal at each refueling cycle. Human error could occur as a result of improper installation procedures. Problems, however, could be identified during prestart-up inspection. The lower head bolts are not removed during refueling and they could be susceptible to common cause failure resulting from local bolt corrosion leading to several simultaneous bolt failures. A certain percentage of these bolts are inspected at each outage and the assumption is that inspection would not be effective in identifying the degradation prior to failure. These requirements may uncover the likelihood of common cause errors leading to some latent failure that is not immediately evident and shed light on other possible failure mechanisms. An example of a common cause failure is a torque wrench/tensioner which is out of calibration so that all bolts are improperly installed and then can possibly fail during operation.

CRDM connections far outside of the reactor could be welded, bolted, or threaded and seam welded. The degradation mechanism would be a function of the specific connection. For instance, welded connections would be susceptible to the mechanisms and loading discussed previously for CRDM components.

Bolted CRDM connections would be subject to steam cutting, boric acid corrosion, aging and other degradation mechanisms that are unique to bolts. It must be stressed that the CRDM connections in this table refers to the CRDM which connects to the drive mechanism. Inboard connections are considered to be part of the “CRDM piping system” discussed earlier. For bolted connections, this demarcation line is the flange joint. The group identified failure data for CRDM leakage from bolted flanged connections.

Component	Geometry	Material	Degradation Mechanisms	Loading	Mitigation/ Maintenance	Comment
Vessel Head Bolts		high strength steel	GC, FDR, UA		Human error	Removal leading to human error (common cause failure) during refueling
RPV wastage		SSC-LAS LAS	GC, FDR, UA, MA			LAS = some BWR upper head, Boric acid wastage (upper & lower head, shell)
CRDM connections		SS	FDR, UA			welded, bolted, threaded + seal weld
CRDM	4-6	A600 base nozzle, SS, C­SS, and NB — LAS housing with NB weld	SCC, TF, MF, LC, GC, FDR, UA	P, S, T, RS, DW, O	HREPL, ISI w TSL, REM	Nozzles and piping up to connection
Nozzles		LAS, SSC-LAS,	TF, MF, LC, GC, SCC, FDR, UA			LAS = BWR only
ICI	< 2”	304 SS, 316 SS	MF, SCC, TF, FW, FDR, UA	P, S, T, RS, DW, O, V	ISI w TSL, REM
RPV Corrosion Fatigue		SSC-LAS LAS	LC, MF, MA FDR, UA			LAS = some BWR upper head, Initiate at cladding cracks (upper & lower head, shell)
BWR penetrations		SS	SCC, LC, FDR, UA			Stub tubes, drain line, SLC, instrumentation, etc.
PWR penetration		SS, A600	SCC, FDR, UA, LC, MF, TF

NB-LAS = nickel-based clad low alloy steel SR = Stress Relaxation and loss of preload

There are two RPV degradation mechanisms which were specifically discussed. The first was degradation of the shell, upper head, or lower head due to boric acid corrosion. The second mechanism was corrosion fatigue developed at through-thickness cladding cracks in the shell, upper head, or lower head. The nozzle category is subject to similar degradation mechanisms as in the attached piping. It should be stressed that the nozzle category only considers the flared portion of the nozzle up to the reactor shelf. The nozzle safe end was earlier defined as part of the piping system. The group identified that some data on nozzle issues exists.

Valve failure modes are summarized in Table B.1.15. The cast stainless steel valve bodies are susceptible to an array of potential degradation mechanisms. These include cavitation (CAV), thermal fatigue (TF), and material aging (MA). Casting defects (CD) are another particular concern. Failure due to the other

mechanisms listed could initiate at either the defects, or repairs of those defects. The main steam isolation valve (MSIV) body is associated with similar failure modes. Specific failure modes for valve bonnets, and valve bonnet bolts were not discussed. Presumably, bonnet bolt failures would be susceptible to the same failure mechanism of other bolts: aging, boric acid corrosion, steam cutting, etc. The hot leg/cold leg loop isolation valve failure modes were also not discussed. However, failures in these valves could be described in terms of the bonnet, body, or bonnet bolt failure sub-categories listed earlier. It should also be noted that valve sizes are generally consistent with the piping system where they are located.

Table B.1.15 Valve Failure Scenarios Component Geometry Material Degradation Mechanisms Loading Mitigation/ Maintenance Comment Valve Body CS, SS C-SS FAC, CAV, LC, TF, MA, GC, CD, SCC, FDR, UA CS, SS = BWR only Valve Bonnet CS, SS C-SS FAC, LC, GC, SCC, MA, CD, FDR, UA CS, SS = BWR only Bonnet Bolts HS-LAS GC, SCC, FDR, UA SR Hot Leg/Cold leg loop isolation valves FDR, UA MSIV Body CAV, TF, MA, CD HS-LAS = High Strength Low Alloy steel CAV = Cavitation Damage SR = Stress Relaxation and loss of preload (SA540 GrB23, SA193 GrB7)

Steam generator tube rupture (Table B.1.16) can occur from a variety of different mechanisms including thermal fatigue, mechanical fatigue, SCC, and general corrosion. The tubes can also be degraded by mechanical deformation (MECDEF), or denting, during installation, inspection, or cleaning. Steam generator tubes are too small to lead to a LOCA due to a single tube failure. Therefore, multiple tube rupture needs to also be considered in order to achieve a certain size LOCA. There is data which exists for SGTR.

Steam generator failure can also occur at the manway (specifically bolt failure), the steam generator shell, or the nozzles. These various failure modes were also not sufficiently discussed so little information has been defined in Table B.1.16. However, the nozzle failure issues will likely be similar to the associated piping system, while manway bolt failure would be caused by the same types of mechanisms as for other bolt failures.

The pump failure modes (Table B.1.17) are similar to many of the failure modes already discussed for other components. The cast pump bodies are potentially subject to the same degradation mechanisms (CAV, TF, CD, MA) as other cast components. The recirculation (RECIRC) bonnet bolts and RCP nozzle are also susceptible to mechanisms discussed earlier. The only unique mode considers an incipient failure of a pump flywheel which could initiate collateral damage in other components or in other piping systems. There was no appropriate passive pump failure data that was identified by the group.

Component	Geometry	Material	Degradation Mechanisms	Loading	Mitigation/ Maintenance	Comment
Tube Rupture	5/8 to 3/4“ diam.	A600	TF, MF, SCC, GC, LC, FRET, MECHDEF, FDR, UA			single and multiple tube rupture
Manway Bolts		CS, LAS	SCC, GC, LC, SR, FDR, UA
Shell		CS, LAS,	GC, LC, MF, TF, FDR, UA
Nozzles to safe end		SSC-LAS CS, LAS SSC-CS	FAC, SCC, FDR, UA
Tube Sheet Failure		NB-LAS A600	SCC, GC, FRET, MF, FDR, UA

FRET = fretting or mechanical wear

Table B.1.17 Pump Failure Scenarios Component Geometry Material Degradation Mechanisms Loading Mitigation/ Maintenance Comment Pump Body C-SS, SSC-CS CAV., TF, CD, MA, SCC, fatigue RECIRC Bonnet Bolts HS-LAS SCC, GC, SR RCP nozzle Flywheel failure initiating collateral damage — secondary pipe failure HS-LAS = High Strength Low Alloy steel SR = Stress Relaxation and loss of preload (SA540 GrB23, SA193 GrB7)

It is obvious that the non-piping passive LOCA sources have not been nearly as well-defined as the piping system sources, and they must be better defined prior the elicitations. However, due to the number and complexity of the components, the panel realized that it may not be possible to fully define all the variables listed in the tables above. At a minimum, the group decided that it would need isometric drawings for as many of these components as possible.

The manner for arriving at the LOCA contributions of these other components will be similar to the approach followed for the piping contribution. Reference cases will be developed and absolute LOCA estimates will be assigned to those numbers. However, these reference cases will be based strictly on data. The bolded items in Tables B.1.13 — B.1.16 are component failures that are supported by passive — system failure data. This data will first need to be accumulated and analyzed. Karen Gott and Bill

Galyean are possible sources for some of this data. There is an EPRI database called PM-BASIS which consists of mainly active components, but there may be some data on bonnets and packings. Also, Spence Bush may have some data for these components that might be useful to the group. Finally, the group discussed that there may be data available for feed water nozzles.

Once the data is developed, it will be made available to the group. This data will make up the base case information for the non-piping components. The group will also be asked how representative the base case data is for future (end-of-plant-license-renewal) LOCA estimates. The LOCA propensity (for each leak threshold rate) for the components without data will also be queried relative to these base cases. This approach is identical to the development of the piping LOCA contributions discussed earlier.