ML13085A190
| ML13085A190 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 04/22/2013 |
| From: | NRC/NRR/DRA/APLA |
| To: | NRC/NRR/DRA/APLA |
| Snodderly M | |
| References | |
| TAC ME6629, TAC ME6630 | |
| Download: ML13085A190 (44) | |
Text
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-01 The Large Loss of Coolant Accident The numerical impact of this Fact and RAI Not Needed (LOCA) event tree discussion of gross Observation (F&O) on the Internal Events containment failure does not appear Probabilistic Risk Assessment (PRA) The licensee explains that Large LOCA consistent with the stated assumption; in this results is judged very small. Since no fire is not a contributor to fire risk.
instance the discrepancy probably does not consequentially causes a Large LOCA Based on this explanation, the NRC change the conclusion that core damage event, there is no effect of this F&O on staff finds the disposition of the F&O to occurs so late as to not qualify as part of NFPA-805 change evaluations (i.e., the be acceptable.
Large Early Release Frequency (LERF). same contribution occurs in both the before (Significance Level C) and after results).
AS-02 The medium LOCA event tree The disposition for the Internal Events PRA RAI submitted as RAI 21(a)1 discussion on long term cooling states seems model brought the affected Supporting to indicate that more heat removal is required Requirement up to at least Capability In response to RAI 21(a) the licensee than the success criterion. (Significance Level Category (CC) II. explains that the documentation C) related to success criteria was updated. The licensee also explains that consequential Medium LOCAs are very small contributors to fire risk.
Given the additional information the NRC staff finds this deficiency has been appropriately resolved by the licensee.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-03 The Main Steam Line Break Inside The numerical impact of this F&O on the RAI Not Needed Containment (SLBI)event tree discussion Internal Events PRA results is judged very states that the Main Steam Line Break small. Since no fire consequentially causes The licensee explains that Main Steam Outside Containment (SLBO )is covered by a Main Steam Line Break (SLB) event, Line Break is a small contributor to fire the SLBI tree, although the mitigation there is no effect of this F&O on NFPA-805 risk.
requirements of these events are different change evaluations (i.e., the same Based on this explanation, the NRC with respect to isolation and containment contribution occurs in both the before and staff finds the disposition of the F&O to systems. (Significance Level C) after results). be acceptable.
AS-04 In the event tree for Station Black-Out The numerical impact of this F&O on the RAI submitted as RAI 21(c)1 (SBO), existing logic for Auxiliary Feed Water Internal Events PRA results is judged to be (AFW) functions asked successively does not zero. Either path through a failure branch In response to RAI 21(c) the licensee require correlation between success of the requires three failed AFW flow paths. explains that this minor logic error is prior branch and the failure of the latter Common Cause Failures (CCFs) are only applicable to the internal events SBO event tree.
branch. (Significance Level C) included in first possible failure path. Since there is no effect on the Internal Events Given the additional information, the PRA model, this F&O has no impact for NRC staff finds the disposition of the NFPA-805. F&O to be acceptable.
AS-05 Although no inconsistencies in This is a documentation issue that has no RAI submitted as RAI 21(c)1 modeling of systems to meet the safety effect on the Internal Events PRA model, functions were identified, there is no and, as a result, there is no effect of this In response to RAI 21(c) the licensee discussion of functional failure criteria for the F&O on NFPA-805. explains that events tree modeling is event trees. (Significance Level C) based on the EOPs and system failures explicitly.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-06 The success criterion for feed and This F&O implies that the success criterion RAI Not Needed bleed is conservative compared to the used for feed and bleed is also criterion used for some other 4-loop conservative in the Fire PRA. Given the The licensee explains that modeling Westinghouse plants. (Significance Level C) abundant AFW availability at CNP, the used in the fire PRA is conservative.
numerical impact of this bleed and feed Based on this explanation, the NRC conservatism is judged very small for the staff finds the disposition of the F&O to Internal Events PRA model. The numerical be acceptable.
effect of such conservatism would be to increase the Core Damage Frequency (CDF) for fires that affect the systems used to perform bleed and feed. This would cause the Fire PRA to be more conservative in feed and bleed scenarios since less fire-related damage can cause failure of the function. This additional conservatism would increase the fire risk estimated for NFPA-805 change evaluations.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-07 Initiating event dependencies are not The disposition for the Internal Events PRA RAI submitted as RAI 21(a)1 retained by event tree transfers. (Significance model brought the affected Supporting Level A) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that 34 event tress were developed to explicitly consider transfer from one event tree to another given failure specific failures of support systems. The licensee listed the support systems and transfer modeling.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
AS-08 Reactor Coolant Pump (RCP) Seal The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 LOCA modeling in the loss of service water model brought the affected Supporting event trees is different than in the SBO event Requirement up to at least Capability In response to RAI 21(a) the licensee trees and needs to be made consistent. Category II. explains the modeling and modeling (Significance Level B) assumptions specific to RCP seal LOCAs.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-09 After recovery of Alternating Current The numerical impact of this F&O on the RAI Not Needed (AC) power, after SBO, the PRA Internal Events PRA results is judged very conservatively requires recovery for small. Pump recovery failure in the internal The licensee explains that modeling alignment of Safety Injection (SI), Charging events PRA model is dominated by used in the fire PRA is conservative.
and Volume Control System (CVCS), operator actions. The effect of this F&O Based on this explanation, the NRC Containment Spray (CTS), and AFW, would be an increase in predicted fire risk staff finds the disposition of the F&O to however, the systems may not be needed or following fire-induced SBO, since op be acceptable.
may be initiated automatically. (Significance actions are more complicated. This would Level C) increase the fire risk estimated for NFPA-805 change evaluations.
AS-10 The event trees do not include a The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 heading for containment isolation failure, model brought the affected Supporting resulting in improper assignment of LERF. Requirement up to at least Capability In response to RAI 21(a) the licensee (Significance Level B) Category II. explains that rather than changing all events trees to include CI, the LERF fault tree was modified to include CI.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
AS-11 Dependencies between the failures The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 causing Interfacing Systems Loss of Coolant model brought the affected Supporting Accidents (ISLOCA) in the individual ISLOCA Requirement up to at least Capability In response to RAI 21(a) the licensee scenarios and the systems mitigating ISLOCA Category II. explains that the ISLOCA initiating are not considered. (Significance Level B) event and event trees were revised to follow the guidance in NUREG/CR-5102 and that initiator and scenarios dependencies were explicitly considered..
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
AS-12 The ISLOCA analysis assumes low The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 pressure piping failure probability based model brought the affected Supporting solely on engineering judgment. (Significance Requirement up to at least Capability In response to RAI 21(a) the licensee Level B) Category II. explains that the ISLOCA initiating event and event tree have been revised to incorporate the guidance in NUREG/CR-5744 and NUREG/CR-5102.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
AS-A1, AS-B1, AS-B2, AS-B4, AS-B5, SY-C1 This issue only impacts the Internal Events RAI submitted as RAI 21(c) 1 The split fraction dependencies and PRA model documentation. This issue does corresponding values (basis) are not well not affect NFPA-805 change evaluations. In response to RAI 21(c) the licensee documented or described in the report. For explains that quantification was example, top event "CSR" has 21 split performed using linked fault trees not split fractions.
fractions (each with a different value) identified in the CCW event trees. However, Based on this explanation, the NRC the only way to follow what the dependencies staff finds the disposition of the F&O to are and how the different fraction values are be acceptable.
calculated, is to go to the WINNUPRA calculation files. Even using the WINNUPRA 6
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) files, not all boundary conditions could be determined.
AS-A1, QU-C3 The number of considered This issue was addressed in a 2007 update RAI Not Needed transfers is too large; even very unlikely that included simplifying the event tree transfer events are modeled (<1E-08/yr). For transfers. The PRA Model was updated in 2007 example, the Initiating Event frequency for to address this concern.
Medium LOCA, transferred from a loss of DC Based on this explanation, the NRC is 8E-9/yr. Even at this low frequency, this staff finds the disposition of the F&O to combined event is still modeled and there is be acceptable.
an event tree associated with AS-A10, AS-B3, SC-A6 ISLOCA modeling This issue relates specifically to the Internal RAI Not Needed should: (1) separate the human reliability Events PRA model. Since no fire (OIB) and hardware (valve) reliability when consequentially causes an Interfacing In the April 27 RAI response for this modeling potential isolation of the appropriate Systems LOCA on one of the modeled F&O, the licensee explains that no breaks, (2) address valve shutoff delta-P pathways, there is no effect of this F&O on credit was given in the fire PRA mitigating fire induced ISLOCA.
capability for valves credited for isolation, (3) NFPA-805 change evaluations (i. the same valve failure rates indicative of functional contribution occurs in both the before and Given the additional information, the degradation due to harsh environment for after results). NRC staff finds the disposition of the Residual Heat Removal (RHR) pump seal F&O to be acceptable.
failure events, (4) operations procedures 7
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) should address remote manual isolation of ISLOCA events.
AS-A10, SC-A12, SC-A18, SY-A3, SY-A5, The numerical impact of this SR on the RAI Not Needed SY-A6, SY-A7, SY-B1, SY-B16 Enhance Internal Events PRA results is judged very AFW system modeling related to Condensate small. The Gap assessment commented In the April 27 RAI response for this Storage Tank (CST) refill by adding a that the approach used was reasonable F&O, the licensee explains that the discussion about CST refill system given the supporting information available, internal events SBO event tree was not used in the fire PRA..
boundaries, capacities and dependencies, but that providing additional system detail and any potential CCF modes. Also, model and separating the HEP and hardware Given the additional information, the the HEP separate from the hardware. would be a benefit to the model. The Fire NRC staff finds the disposition of the PRA has accounted for the possibility that F&O to be acceptable.
one or more fire initiators could preclude refilling the CST, so the effect of this SR is implicit in NFPA-805 results.
AS-A2-01 The accident sequence notebook The development of accident sequences RAI Not Needed does not identify the safety functions did inherently consider safety functions necessary to reach a safe and stable state to required to reach a safe, stable state by In the April 27 RAI response for this prevent core damage following the initiating virtue of the historical development of the F&O, the licensee explains that event events. (Finding) Event Trees and by following the EOPs tree modeling is based on EOP response and corresponding system which are based on assuring that the safety function.
functions are met. This is a documentation issue that has no numerical impact on the Given the additional information, the Internal Events PRA model. This issue NRC staff finds the disposition of the does not affect NFPA-805 change F&O to be acceptable.
evaluations.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
AS-A5 Consider a review and update of The Internal Events PRA model was RAI Not Needed MAAP analyses for success criteria pertaining updated to account for the addition of SDGs to accident sequence development to the plant in 2005. As part of this model The SBO and RCP seal LOCA associated with SBO and RCP Seal LOCA. update improved event tree modeling and modeling was updated in 2005.
success criteria were adopted for RCP seal Based on this explanation, the NRC LOCAs.
staff finds this deficiency has been appropriately resolved by the licensee.
AS-B3, LE-D1, LE-D6 Address if there are The containment pressure relief operation RAI Not Needed any phenomenological interactions that the failure rate is so small that it has not should be considered as potential failure been included in the fault tree model. The In the April 27 RAI response for this modes of containment isolation. In the failure probability is the product of the time F&O, the licensee explains review of containment isolation model, I&M should fraction and two isolation valves failing, pressure relief operation was performed and model impact consider accounting for the possibility of up to which is more than two orders of magnitude assessment performed that concluded 200 hrs per year (2.3E-02) containment purge lower than the than the highest failure low probability of occurrence.
operation when purge valves could be open cutset probability that results in the same and could randomly fail to close on demand. effect on containment isolation. With Given the additional information, the respect to the remaining issue, the Gap NRC staff finds this deficiency has assessment commented that there should been appropriately resolved by the not be any phenomenological interactions licensee.
that are potential failure modes of containment isolation. This issue only impacts the Internal Events PRA model documentation. This issue does not affect NFPA-805 change evaluations.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
DA-01 The data collection notebook provides The Internal Events PRA model update in RAI Not Needed a description of the criteria, in terms of 2009 included revising failure data for evidence, for performing a Bayesian update Mitigating Systems Performance Indicator Calculation and Bayesian updating has which is inconsistent with industry references (MSPI) pumps and diesels, accounting for been performed. Documentation and the guidelines for common cause failure the latest plant-specific failure data. The remains to be updated.
data analysis seems to not be in accordance 2009 calculation was performed in Based on this explanation, the NRC with the cited reference. (Significance Level accordance with NURG/CR-6928, including staff finds the disposition of the F&O to C) Bayesian updating. In addition, a CCF be acceptable.
update was also performed consistent with the latest industry and NRC guidance. The remaining issue from this F&O is related to updating the notebook to discuss/reference the methodologies employed. This remaining documentation issue does not affect NFPA-805.
DA-02 The method used to perform The Internal Events PRA model update in RAI Not Needed Bayesian updates is often described as 2009 included revising failure data for MSPI moment matching, which in some cases may pumps and diesels, accounting for the Calculations have been performed per yield misleading results. (Significance Level latest plant-specific failure data. The 2009 industry guidance. Documentation C) calculation used generic data distributions remains to be updated.
from NURG/CR-6928, Bayesian updated Based on this explanation, the NRC per NUREG/CR-6928, and mapped the staff finds the disposition of the F&O to results to the natural conjugate. No moment be acceptable.
matching was performed to obtain the prior distribution. The remaining issue is related to updating the documentation and does not affect NFPA-805.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
DA-03 General guidelines for test and The Internal Events PRA model update in RAI Not Needed maintenance data collection are provided, 2009 included revising failure data for MSPI however, the boundaries of the components pumps and diesels, accounting for the Calculations have been performed per and subsystems to be included in latest plant-specific failure data. The 2009 industry guidance. Documentation maintenance basic event were not defined in calculation identified the data to be remains to be updated.
the data collection sheets or in the data collected and the sources for the data. The Based on this explanation, the NRC notebooks. (Significance Level C) remaining issue is related to updating the staff finds the disposition of the F&O to documentation and does not affect NFPA- be acceptable.
805.
DA-04 Multiple Greek Letter (MGL) The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 parameters from Table 5-11 of NUREG/CR- model brought the affected Supporting 5485 were used to obtain CCFs for some Requirement up to at least Capability In response to RAI 21(a) the licensee components in the CNP PRA There are Category II. explains specific modeling changes to limitations on using such data, which I&M did common cause modeling and the rationale for those changes related to not appear to observe At least one of the three suggested resolutions.
reviewers felt that the significance of this observation should be B, given the rationale Given the additional information, the above. AEP PRA personnel indicated that: NRC staff finds this deficiency has they understood the individual issues been appropriately resolved by the identified; that the issues regarding licensee.
assumptions were primarily documentation rather than results impacts; and that the issue of which generic data source is appropriate is generic and, to some extent, a matter of preference, and that they are comfortable with the approach they have used. The significance C has been assigned on the 11
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) basis of this understanding, but AEP is encouraged to consider the suggested resolutions noted below. (Significance Level C)
DA-05 Plant specific screening of generic The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 common cause failure data is insufficient and model brought the affected Supporting component boundaries defined for common Requirement up to at least Capability In response to RAI 21(a) the licensee cause modeling have not been verified. Category II. explains that plant specificity was (Significance Level B) incorporated into the modeling for common cause terms having a Fussell Vessely importance measure greater than 1%. The licensee also confirmed that the data compilation was performed consistent with the component boundaries and explained common cause modeling related to 12
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) specific components.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
DA-06 The 4160 and 600VAC Electric The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 System Notebook lists the common cause model brought the affected Supporting failure group for the Emergency Diesel Requirement up to at least Capability In response to RAI 21(a) the licensee Generators (EDGs) as being the Unit 1 Category II. explains that common cause failure EDGs, however, all four EDGs belong to a groups were established per unit since EDGs are not shared and cannot be single common cause group. (Significance cross-tied.
Level D)
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
DA-07 The data notebook does not indicate The Internal Events PRA model update in RAI Not Needed that a systematic approach was used to 2008 included revising CCF groups and identify plant specific common cause failure data. This effort systematically redefined Calculations have been performed per groups. (Significance Level C) the CCF groups in a manner consistent with industry guidance. Documentation industry guidance. The remaining issue remains to be updated.
from this F&O is related to updating the Based on this explanation, the NRC notebook to discuss/reference the staff finds the disposition of the F&O to methodologies employed. This remaining be acceptable.
documentation issue does not affect NFPA-805.
DA-08 The degree of conservatism in the The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 "unique unavailabilities" is not in all cases model brought the affected Supporting either best estimate known to be Requirement up to at least Capability In response to RAI 21(a) the licensee 13
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) conservative, but this is judged not to have a Category II. explains that the probability of PORV significant effect on the results at this time. challenge following other plant (Significance Level C) transients is based on generic data updated with plant specific data and considers that the approach is reasonable given sparse data.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
DA-09 Data notebook was not signed by the The data notebook has been updated twice RAI Not Needed reviewer indicated on its cover of notebook, (once completely, Rev. 3 and once partially, so it is not clear the document has actually Rev. 3 CS-1) and additional supporting The documentation was updated.
been reviewed by the reviewer, and, the calculations have been completed since document has not been approved. this F&O was written. All documents have Based on this explanation, the NRC staff finds this deficiency has been (Significance Level C) been signed in accordance with applicable appropriately resolved by the licensee processes. No further disposition required for Internal Events PRA model. This F&O does not affect NFPA-805.
DA-C1 In many cases there is no description This issue only impacts the Internal Events RAI submitted as RAI 21(a) 1 for the basic events or the description lacks PRA model documentation. This issue does sufficient detail to understand what the basic not affect NFPA-805 change evaluations. In response to RAI 21(c) the licensee event is modeling. explains that cited information exists not in a single listing but several controlled documents.
Given the additional information, the NRC staff finds the disposition of the 14
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
F&O to be acceptable.
DA-C1 Provide a clear description of the The data collection did consider established RAI Not Needed boundaries that make up each basic event. boundaries but did not include references to Such a description is provided only for the the boundary definitions that were used. The licensee explains that data EDGs and is not provided consistently for This is a documentation issue that has no collection did consider established other basic events. numerical impact on the Internal Events boundaries but documentation remains to be updated.
PRA model. This issue does not affect NFPA-805 change evaluations. Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
DA-C1 There is inconsistency in describing This issue only impacts the Internal Events RAI submitted as RAI 21(c) 1 dominant basic events in the systems PRA model documentation. This issue does analyses. For example, the CCW system note not affect NFPA-805 change evaluations. In response to RAI 21(c) the licensee book describes an important contributors to explains that the PRA system system unavailability as heat exchanger notebooks were revised subsequent to the F&O finding.
rupture but the basic event modeled is tube plugging Given the additional information the NRC staff finds this deficiency has been appropriately resolved by the licensee.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
DA-D4-01 A Bayesian update process was The Bayesian updated data have been RAI Not Needed used to combine industry-generic and plant- reviewed and appear to be reasonable.
specific data for pumps and emergency diesel This issue impacts the Internal Events PRA The licensee explains that Bayesian generators. No documentation or discussions model documentation. This issue does not updated data have been reviewed for with the utility demonstrated that the posterior affect NFPA-805 change evaluations. reasonableness.
distributions were checked for Based on this explanation, the NRC reasonableness. (Finding) staff finds the disposition of the F&O to be acceptable.
DA-D6-01 Review of the CCF Notebook The numerical impact of this F&O on the RAI submitted as RAI 21(c) 1 shows that EDG CCFs for failure to start and Internal Events PRA results is judged very failure to run were calculated s separately small. Since these failures are independent In response to RAI 21(c) the licensee from the associated room cooling fans. These of fire initiators, there is no effect of this explains the decision to model EDH CCF values are based on NUREG/CR-5497 F&O on NFPA-805 change evaluations cooling fans separately from the EDG and that the modeling is conservative.
generic CCF parameters that include the (i.e., the same contribution occurs in both EDG room fans within the boundary of the the before and after results). Given the additional information, the EDG. The explicit modeling of the EDG room NRC staff finds the disposition of the cooling fans may lead to additional F&O to be acceptable.
conservatism of EDG sub-components.
(Suggestion)
DA-E2-01 Error factor (characterization of This issue only impacts the Internal Events RAI submitted as RAI 21(c) 1 uncertainty) discrepancies were identified PRA model documentation. This issue does between supporting calculation reports. not affect NFPA-805 change evaluations. In response to RAI 21(c) the licensee (Finding) explains that discrepancy was a documentation error and further explains that the uncertainty analysis for the fire PRA is, in any event, performed separately.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
DA-E2-01 There is evidence to suggest that The data collection did consider established RAI Not Needed established component boundaries were boundaries but did not include references to considered in the data collection process, but the boundary definitions that were used. The licensee explains that the data the component boundary definitions that were This is a documentation issue that has no collection effort did consider used were not stated or referenced. numerical impact on the Internal Events established boundaries but did not reference the definitions used. The Component boundary definitions should be PRA model. This issue does not affect documentation remains to be developed and included or cited as reference. NFPA-805 change evaluations. improved.
(Finding)
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
DA-E3-01 The sources of key uncertainty The numerical impact of this F&O on the RAI Not Needed associated with the data analysis were not Internal Events PRA results was judged clearly documented. (Suggestion) very small. This issue will be separately The licensee explains that addressed for the Fire PRA model documentation of key sources of developed in support of NFPA-805. uncertainty was performed for the fire PRA.
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
DE-01 A procedure which is less systematic The disposition for Internal Events PRA RAI submitted as RAI 21(a) 1 than NUREG/CR-4780 was used to develop model Significance Level B F&O DE-02 the component groups for common cause, also addresses this F&O, so this Supporting In response to RAI 21(a) the licensee explains that common cause failure 17
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) however, the groupings used are reasonable. Requirement was also brought up to at (CCF) was modeled according to (Significance Level C) least Capability Category II. industry guidance and points out that CCF approach was reviewed in the 2009 focused scope peer review Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
DE-02 CCF groupings appear to be The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 inconsistent with respect to whether running model brought the affected Supporting and standby components are grouped Requirement up to at least Capability In response to RAI 21(a) the licensee together. (Significance Level B) Category II. explains that common cause failure (CCF) was modeled according to industry guidance and points out that CCF approach was reviewed in the 2009 focused scope peer review Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
HR-01 Cause-Based Decision Tree Method This issue relates specifically to the Internal RAI Not Needed (CBDTM) was used for quantification of the Events PRA model. Operator actions post accident cognitive errors, but use of analyzed for Fire-response are performed Modeling used in the fire PRA is CBDTM alone may result in conservative and in accordance with Fire PRA guidance. conservative.
non plant specific Human Error Probability Accordingly, there is no effect of this F&O Based on this explanation, the NRC (HEP) values which may shadow actual on NFPA-805 change evaluations (i.e., the staff finds the disposition of the F&O to important risk contributors. (Significance same contribution from this issue occurs in be acceptable.
Level C) both the before and after results).
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
HR-02 Miscalibration of instruments was not The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 addressed. This may result in model brought the affected Supporting underestimation of actual risk since Requirement up to at least Capability In response to RAI 21(a) the licensee miscalibration can affect multiple trains like a Category II. explains that modeling pre-initiator common cause failure. (Significance Level B) human errors, including miscalibration errors, is included in the licensees Fault Tree Modeling Guidelines.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
HR-03 Use of bounding HEPs was identified. The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 Use of bounding HEPs will produce model brought the affected Supporting unrealistic results and may shadow actual Requirement up to at least Capability In response to RAI 21(a) the licensee dominant contributors to the risk. Category II. explains that all operator actions were (Significance Level B) re-evaluated for use in the fire PRA and were peer reviewed for the fire PRA.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
HR-04 Table 1 in the Human Reliability This F&O was explicitly addressed by a RAI Not Needed Analysis (HRA) notebook is confusing and subsequent HRA-related calculation. This is there should be some additional explanation a documentation issue with no numerical This is a documentation issue.
provided about what the Table is presenting, effect on the Internal Events PRA model.
to aid in understanding how the information is As a result, there is no effect of this F&O on Based on this explanation, the NRC staff finds the disposition of the F&O to tied to the PRA model and results. NFPA-805.
be acceptable.
(Significance Level C) 19
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
HR-C1 F&O #SY-9 stated that in part, In a No examples of basic events that combined RAI Not Needed couple of places in the SI and AFW system an operator action and hardware (or models, hardware failures are not explicitly ignored hardware) in the Internal Events The licensee explains that it could find modeled because they are dominated by PRA SI system model were provided in the no cases of basic events that operator action failures. The thrust of this F&O, nor could any be identified. However, combined operator actions and hardware but that in a previous version F&O was on the AFW system as related to it is noted that in the PRA model prior to the of the PRA that F&O had been made.
the modeling of CST refill. However, there 2003 F&O response update, RCP trip was no apparent disposition of the SI model failure following loss of service water Based on this explanation, the NRC for combining a human action with hardware initiators only included HEPs. In this case, staff finds the disposition of the F&O to failures into a single basic event. These appropriate hardware failures were added be acceptable.
single HEP basic events can sometimes into the fault tree as part of the 2003 F&O mask importance/success of the related model update. Per the preceding SR hardware. discussion, the Fire PRA has addressed the CST portion of this SR, so the effect of this SR is implicit in NFPA-805 results.
HR-G6-01 There is no evidence that DC A complete review of the HEPs and a HEP RAI Not Needed Cook checked the internal consistency of the dependency analysis have been performed HEPs either for the three Human Failure for earlier versions of the Internal Events The licensee explains that a complete Events (HFEs) covered by this review or their PRA model. These documents were not review of the HEPS and HEP complete set of HFEs, although there is no included in the list of references made dependency was performed for the internal events PRA. The response for appearance of inconsistency. (Finding) available to the Peer Review team. This RAI 211 provides further explanation issue impacts the Internal Events PRA that all HEPS were reevaluated for the model documentation. This issue does not fire PRA.
affect NFPA-change evaluations.
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
20
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
IE-01 The sum of the mean values for the The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 lognormal distributions that describe the model brought the affected Supporting generic single and dual unit loss of offsite Requirement up to at least Capability In response to RAI 21(a) the licensee power frequency derived are in the range of Category II. explains that the error factors were other generic estimates but their variance updated to consistent with generic estimates and the source of each error appears lower. (Significance Level C) factor was added to initiating events notebook. The licensee also points out that initiating events error factors are not germane to the fire PRA.
Given the additional information the NRC staff finds this deficiency has been appropriately resolved by the licensee.
IE-02 There are several cases where an The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 initiating event category with more severe model brought the affected Supporting impact is subsumed by another category with Requirement up to at least Capability In response to RAI 21(a) the licensee less severe impact. This may have a Category II. explains that in response to this Level significant effect on the calculated CDF. B finding initiating event categories were reviewed and revised. The (Significance Level B) licensee also points out that internal event initiators were not used in the fire PRA.
Given the additional information the NRC staff finds this deficiency has been appropriately resolved by the licensee.
21
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
IE-03 It appears that all initiator categories The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 are accounted for, but a cross reference model brought the affected Supporting mapping categories to an acceptable source Requirement up to at least Capability In response to RAI 21(a) the licensee would ensure completeness. (Significance Category II. explains that documentation was Level C) updated to include cross reference.
The licensee also points out that internal event initiators were not used in the fire PRA.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
IE-04 Although the initiators retained for This issue relates specifically to the Internal RAI Not Needed system losses that lead to initiating events Events PRA model. There is no effect of seem reasonable, the structured process this F&O on NFPA-805 cha evaluations Documentation issue used to obtain these results was not (i.e., the same contribution from this issue discussed in the model documentation. occurs in both the before and after results). Based on this explanation, the NRC staff finds the disposition of the F&O to (Significance Level C) be acceptable.
IE-05 A single value is used for the probability The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 of pressurizer Power Operated Relief valve model brought the affected Supporting (PORV) or safety valve challenge following all Requirement up to at least Capability In response to RAI 21(a) the licensee transients, without any other considerations Category II. explains that the probability of a PORV for how the probability might depend on the challenge were determined in accordance with methodology used in transient. (Significance Level B)
NUREG/CR for Sequoah and determined separate values following LOSP and loss of DC power.
22
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
IE-07 The Loss of Direct Current (DC) The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 initiating event was quantified by fault tree model brought the affected Supporting analysis and obtains results that are not Requirement up to at least Capability In response to RAI 21(a) the licensee comparable result to other plants. Category II. explains that tin response to this Level (Significance Level B) B finding specific modeling changes were made.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
IE-C1 A good justification is lacking for why This issue only impacts the Internal Events RAI submitted as RAI 21(c) 1 earlier years of operational experience are PRA model documentation. This issue does excluded (207 trips) in the plant trip initiation not affect NFPA-805 change evaluations. The licensee explains that internal frequency. Note, however, that these trips are events PRA model initiators were not accounted for when evaluating the PORV used in the fire PRA.
challenge frequency.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
IF-B3-01 Flood source flow rates and The numerical impact of this F&O on the RAI Not Needed capacities were determined without Internal Events PRA results is judged very considering source temperatures. It also small. Since these failures are independent Fire induced flooding cannot have a appears that High Energy Line Break (HELB) of fire initiators, there is no effect of this significant impact on the fire PRA.
was excluded from the Internal Flood F&O on NFPA-805 change evaluations Based on this explanation, the NRC Analysis because it was performed (i.e., the same contribution occurs in both staff finds the disposition of the F&O to 23
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) separately. (Suggestion) the before and after results). be acceptable.
IF-C3-01 The Systems, Structures and This issue only impacts the Internal Events RAI Not Needed Components (SSCs) affected by any given PRA model documentation. This issue does flood are listed in an Attachment of a PRA not affect NFPA-805 change evaluations. Fire induced flooding cannot have a calculation. However, the list does not identify significant impact on the fire PRA.
the specific flood-induced failure mechanism Based on this explanation, the NRC for these SSCs. (Suggestion) staff finds the disposition of the F&O to be acceptable.
L2-01 Editorial Comment: Section 3.0 This documentation issue has no numerical RAI Not Needed reference to DG-1061 should be changed to implications for the Internal Events PRA RG-1.174. (Significance Level D) model. Accordingly, there is no effect of this The editorial correction remains to be F&O on NFPA-805. corrected.
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
L2-02 The impact of containment failure prior This issue relates specifically to the Internal RAI submitted as RAI 21(c) 1 to core mode has been evaluated with Events PRA model. There is no effect of respect to LERF, assuming that offsite this F&O on NFPA-805 change evaluations In response to RAI 21(c) the licensee protective actions would have directed (i.e., the same contribution from this issue explains the assumption is related only evacuation of the surrounding population prior occurs in both the before and after results). Large LOCAs and Large LOCA is not a contributor to fire risk.
to core damage, and this may not be 24
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) reasonable for large LOCA initiated Given the additional information, the sequences. (Significance Level C) NRC staff finds the disposition of the F&O to be acceptable.
L2-03 At CNP, actions to depressurize the This issue identifies that the Internal Events RAI Not Needed Reactor Coolant System (RCS), e.g., open PRA model conservatively determines PORVs, at the onset of core damage have LERF because no credit is taken for The model is conservative as no credit been moved from the Emergency Operating opening PORVs (whether directed by EOPs is taken for depressurizing RCS.
Procedures (EOPs) to the Severe Accident or SAMGs) to lower RCS pressure after the Based on this explanation, the NRC Mitigatino Guidelines (SAMGs), which may onset of core damage. Although this staff finds the disposition of the F&O to impact the generic containment failure approach is consistent with the guidance be acceptable.
probabilities in the simplified LERF model, provided for the simplified LERF model since they implicitly include the likelihood of used, the CC for this sub-element is I. This such action. (Significance Level C) over-estimate of LERF implies that NFPA-805 change evaluations will obtain more limiting delta-LERF values than a more realistic model achieving a CC II.
L2-04 The LERF calculation omitted The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 containment isolation failure from the LERF model brought the affected Supporting equation based on its low probability, but Requirement up to at least Capability In response to RAI 21(a) the licensee neglected the contribution due to "pre-existing Category II. explains that in response to this Level failures." (Significance Level B) B finding the containment isolation notebook was updated to address the cited omissions.
Given the additional information, the 25
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
NRC staff finds this deficiency has been appropriately resolved by the licensee.
L2-05 Generic split fractions from the The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 NUREG/CR-6595 simplified LERF model are model brought the affected Supporting assumed to apply without any specific Requirement up to at least Capability In response to RAI 21(a) the licensee evaluation to support the assumption. Category II. justifies continued use of the split (Significance Level B) fractions from NUREG/CR 6595 based on similarity of design features between the Sequoyah and DC Cook plants.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
LE-A1, LE-B1, LE-C3, LE-C4, LE-D1, LE-E1 This SR implies that the LERF model is RAI Not Needed Use of NUREG/CR 6595 for containment also conservative for the Fire PRA. The modeling is considered conservative and is numerical effect of such conservatism The modeling used in the fire PRA is considered by RG-1.200 to be Capability would be to increase the predicted LERF conservative.
Category I. for fire initiators. This conservatism would Based on this explanation, the NRC increase the fire risk estimated for NFPA-staff finds the disposition of the F&O to 805 change evaluations based on LERF. be acceptable.
26
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
MU-01 Draft PRA Maintenance and Update The PRA Maintenance and Update RAI Not Needed Procedure could be improved by focusing the Procedure was finalized. Specific direction list of criteria on key items with specific for calculation preparers and reviewers to The PRA Procedure was updated in actions or directions for analysts. use guidance in the applicable standards is response to F&O.
(Significance Level C) included. This procedure revision was Given this information, the NRC staff performed to satisfy an F&O from t Fire finds this deficiency has been PRA Peer Review. Accordingly, there is no appropriately resolved by the licensee.
effect of this F&O on NFPA-805.
MU-02 There is not currently a formal The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 procedure or process for the control of the model brought the affected Supporting PRA models. (Significance Level B) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains their formal process and procedures involved for maintaining configuration control over the PRA per the recommendation in this Level B finding.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
QU-02 A house event structure for Loss of The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 DC has been incorrectly developed in fault model brought the affected Supporting trees developed for Component Cooling Requirement up to at least Capability In response to RAI 21(a) the licensee Water (CCW) and possibly Essential Service Category II. explains the fault tree modeling has Water (ESW). (Significance Level B) been reviewed and modified per the recommendation in this Level B finding.
Given the additional information, the 27
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
NRC staff finds this deficiency has been appropriately resolved by the licensee.
QU-03 The calculation of ISLOCA initiating The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 event frequency does not consider correlated model brought the affected Supporting failures of valves in series, i.e., RHR Requirement up to at least Capability In response to RAI 21(a) the licensee discharge and suction (Significance Level B) Category II. explains that it adapted methodology from NUREG/CR 5744 to calculate ISLOCAs to consider correlated failures of valves in series to address this Level B finding.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
QU-04 Some loss of CCW and ESW The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 sequences involving tripping the RCPs, model brought the affected Supporting depressurizing the RCS, and restoring CCW Requirement up to at least Capability In response to RAI 21(a) the licensee or ESW, appear to be overly optimistic. Category II. describes changes in models and (Significance Level B) documentation to explicitly address this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
28
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
QU-05 Multiple frequency truncation limits are Adequate convergence is demonstrated by RAI Not Needed used in the quantification for different events. comparison of the latest Internal Events There is evidence that the model results tend PRA model results for cases with truncation The licensee states that truncation was to converge as the truncation is lowered, levels at least 5 and 7 orders of magnitude established using the convergence however, demonstration of results below event probability (e.g.,. CDF increase method but that documentation remains to be updated.
convergence could be enhanced. < 5%). The remaining issue from this F&O (Significance Level C) is related to documentation and does not Based on this explanation, the NRC affect NFPA-805. staff finds the disposition of the F&O to be acceptable.
QU-06 A formal search performed for unique The numerical impact of this F&O on the RAI Not Needed or unusual sources of uncertainty not present Internal Events PRA results was judged in the typical or generic plant analysis is not very small. This issue will be separately Staff sees that sources of uncertainty sufficiently documented. (Significance Level addressed for the Fire PRA model were examined in the fire PRA C) developed in support of NFPA-805. Uncertainty and Sensitivity Analysis report (PRA-17663-014-LAR).
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
QU-07 There are inconsistencies in the HRA The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 modeling of dependency between RCS cool- model brought the affected Supporting down and depressurization and transfer to Requirement up to at least Capability In response to RAI 21(a) the licensee recirculation. (Significance Level B) Category II. explains that all operator actions were re-evaluated for use in the fire PRA.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
29
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
QU-F5 I&M should consider documenting the This issue only impacts the Internal Events RAI Not Needed process used for independent review of PRA model documentation. This issue does computer code results as part of the PRA not affect NFPA-805 change evaluations. Formalization of computer code general guidance document. validation not likely to lead to PRA results impact.
Also, staff sees that PRA-RAI-002 Rev 0 Attachment 6C (PRA Update Study Report) shows QU-F6 met at CC II (Conditional).
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SC-A2 Explain the potential impact on the The impact of this core damage criterion is RAI submitted as RAI 21(b) 1 model and associated success criteria with limited to a small number of scenarios, i.e.,
regard to the conservative nature of MAAP those for which the inventory makeup In response to RAI 21(b) the licensee analyses which assume a core damage success criterion results in turning around explains their MAAP run strategy and temperature threshold of 1400F. the core temperature excursion after core explains how it is conservative.
temperature exceeds 140 F but before it Given the additional information, the reaches 2200 F. The numerical effect of NRC staff finds the disposition of the such a conservatism may be a larger CDF F&O to be acceptable.
than the assumption of the higher core damage threshold. Since thi conservatism depends on inventory make-up requirements, the estimated Fire CDF may also be larger. This would ten to increase the conservatism in NFPA-805 change 30
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) evaluations since more degraded support states would benefit from the higher core damage threshold.
ST-02 Erroneous screening criteria used for The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 Internal Flooding (IF) Analysis causes under- model brought the affected Supporting prediction of IF Risk. (Significance Level A) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that the approach to internal flooding is only related to internal events, and that the modeling does not affect fire PRA risk.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
31
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
SY-01 The calculation for Unfavorable This issue relates specifically to the Internal RAI submitted as RAI 21(c) 1 Exposure Time (UET) for Anticipated Events PRA model. There is no effect of Transient Without Scram (ATWS) pressure this F&O on NFPA-805 change evaluations In response to RAI 21(c) the licensee relief generally follows the approach defined (i.e., the same contribution from this issue explains that there are no fire-induced in WCAP-11992, however, the calculated occurs in both the before and after results). ATWS sequences in the fire PRA.
UETs are expressed as fraction of cycle Given the additional information, the without adjustment for use in annual CDF NRC staff finds the disposition of the calculations, as specified in the WCAP. F&O to be acceptable.
(Significance Level C)
SY-02 Assumptions about PORV block The numerical impact of this F&O on the RAI Not Needed availability in the PORV logic models appear Internal Events PRA results is judged very to be overly-conservative and not well small if PORV block valve availability is The licensee explains how the supported, while the basis for the air bottle increased. The overly-conservative failure modeling is conservative.
capacity appears to be inadequately probability implies that fire scenarios that Based on this explanation, the NRC documented. (Significance Level C) induce other PORV failure are more likely staff finds the disposition of the F&O to to proceed to core damage. This over- be acceptable.
estimate of PORV failure implies that NFPA-805 change evaluations will be obtain more limiting delta-CDF values than a more realistic model.
SY-03 Editorial Comments for AFW Notebook The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 Assumptions. (Significance Level D) model brought the affected Supporting Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that the editorial correction cited in this Level D suggestion was incorporated.
Given the additional information, the 32
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-04 In the SI system notebook, the The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 success criteria for the different combinations model brought the affected Supporting of pumps required for success are listed Requirement up to at least Capability In response to RAI 21(a) the licensee without specifying the scenarios to which they Category II. explains that the SI system notebook apply. (Significance Level C) was enhanced to provide information requested by this Level C suggestion.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-05 Diversion flow paths that adversely The disposition for the Internal Events PRA RAI submitted as RAI 21(a) April 27, affect success criteria or timing of events may model brought the affected Supporting 2012 have been eliminated without sufficient Requirement up to at least Capability justification. (Significance Level B) Category II. In response to RAI 21(a) the licensee explains that modeling guidance was developed and implemented that include flow diversion path modeling based on this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
33
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
SY-06 Although the high pressure injection The Internal Events PRA model update in RAI Not Needed fault tree includes individual failures of two 2008 included revising CCF groups and series valves whose closure prevents flow data. This effort added the identified CCF The PRA model was revised to model diversion, a small portion of the failure of this group and basic events to the model. This this common cause.
action is missed because the common cause issue does not affect NFPA-805.
Based on this explanation, the NRC factor is neglected. (Significance Level C) staff finds this deficiency has been appropriately resolved by the licensee.
SY-07 Although the PRA modeling approach This is a documentation issue that has no RAI Not Needed for systems with a normally running pump on numerical impact on the Internal Events one train is reasonable, it is not explained in PRA model. This issue does not affect This is a documentation issue.
the SI Notebook where it is used for CVCS NFPA-805 change evaluations. Documentation remains to be updated.
pumps. (Significance Level D)
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
SY-08 Although the model correctly accounts The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 for potential ESW and CTS fouling but the model brought the affected Supporting documentation could be improved. Requirement up to at least Capability In response to RAI 21(a) the licensee (Significance Level D) Category II. explains that description of how heat exchanger plugging was modeled was added.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
34
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
SY-09 In a couple of system models, The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 component hardware failures are not model brought the affected Supporting modeled explicitly because they are Requirement up to at least Capability In response to RAI 21(a) the licensee dominated by operator action failures. Category II. explains that a firmer basis for the (Significance Level B) operator timing was developed and incorporated, and documentation improved to match for this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-10 There seems to be inconsistency The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 between the success criteria and the model brought the affected Supporting implementation in the model for the pressure Requirement up to at least Capability In response to RAI 21(a) the licensee relief success criteria for ATWS. (Significance Category II. explains that ATWS pressure relief Level B) modeling was redone to consider the appropriate success criteria for each unit to address for this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-11 Passive failure modeling in the loss of The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 service water system initiating event logic is model brought the affected Supporting inadequate. (Significance Level A) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that modeling guidance was developed and implemented to passive 35
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) failures in both the initiator and system response modeling to address this Level A finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-12 Common cause failure modeling for The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 250V DC battery chargers was not included in model brought the affected Supporting the model. (Significance Level C) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that common cause failure of battery chargers was added to the DC power supply modeling to address for this Level C finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-13 The documentation provides a This is a documentation issue that has no RAI Not Needed reasonable basis for performing the system numerical impact on the Internal Events analysis and, in general, maintains PRA model. This issue does not affect This is a documentation issue.
consistency with proven approaches, but NFPA-805 change evaluations. Documentation remains to be updated.
does not include a discussion of the potential Based on this explanation, the NRC for initiating events due to system faults, a staff finds the disposition of the F&O to discussion of spatial dependencies, or a table be acceptable.
of both support systems and the effect on the component of the loss of the support system.
36
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
(Significance Level C)
SY-14 The only guidance available for The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 systems analyses is the guidance from the model brought the affected Supporting Individual Plant Examination (IPE). Requirement up to at least Capability In response to RAI 21(a) the licensee (Significance Level C) Category II. explains that fault tree modeling guidance was developed and implemented to address this Level C finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-15 The system notebook for the EDGs This is a documentation issue that has no RAI Not Needed states that the capacity of the EDG day tanks numerical impact on the Internal Events will supply the EDGs for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, but the PRA model. This issue does not affect This is a documentation issue.
notebook does not explicitly identify that fuel NFPA-805 change evaluations. Documentation remains to be updated.
oil is included in the fail-to-run probability.
Given the information, the NRC staff (Significance Level D) finds the disposition of the F&O to be acceptable.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
SY-16 In the PORV fault tree for automatic The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 operation, the hardware required for pressure model brought the affected Supporting sensing and signal generation is not modeled. Requirement up to at least Capability In response to RAI 21(a) the licensee (Significance Level C) Category II. explains that pressure sensors required to open the pressurizer PORVs have been added to all system models to address this Level C finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-17 Cross-tie for AFW from Unit 2 does not The numerical impact of this F&O on the RAI Not Needed consider the need for AFW at Unit 2, so the Internal Events PRA results is judged very fault trees presume both motor driven pumps small. Since no fire consequentially causes The licensee explains that the at Unit 2 are available for supply to unit 1 in the other unit's AFW failure, there is [no] assumption cited in the F&O produces the event the three pumps at Unit 1 fail. effect of this F&O on NFPA-805 change only a small impact to to fire risk.
Based on this the NRC staff finds the (Significance Level C) evaluations (i.e., the same contribution disposition to the F&O to be occurs in both the before and after results). acceptable.
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
SY-18 The fault trees have limited modeling The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 of passive failures, functional failures and model brought the affected Supporting subtle interactions. (Significance Level B) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that modeling guidance was developed and implemented to that explicitly address the several issues 38
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) cited in this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-19 Recovery for ESW and CCW does not The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 consider the cause of failure; NSAC-161 model brought the affected Supporting recovery factors are applied to all system Requirement up to at least Capability In response to RAI 21(a) the licensee failures evenly. (Significance Level B) Category II. explains that the ESW and CCW modeling was modified to specifically address the differing recovery probabilities to address this Level B finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
SY-20 The model correctly includes sump This is a documentation issue that has no RAI Not Needed strainer plugging, but the documentation is numerical impact on the Internal Events incorrect. (Significance Level D) PRA model. This issue does not affect This is a documentation issue.
NFPA-805 change evaluations. Documentation remains to be updated.
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
SY-A15-01 The SDG model does not include This issue only impacts the Internal Events RAI Not Needed pre-existing maintenance errors. Section 5.2 PRA model documentation. This issue does of the SDG notebook discusses pre-existing not affect NFPA-805 change evaluations. This is a documentation issue.
maintenance errors and the basis for Documentation remains to be updated.
excluding them. While the exclusion bases Based on this explanation, the NRC are appropriate, it is suggested that a tie to staff finds the disposition of the F&O to the screening criteria employed be included in be acceptable.
the text. (Suggestion)
SY-A19-01 The Supplemental Diesel The SDG design did consider RAI Not Needed Generator (SDG) notebook does not identify environmental factors since the SDGs are a the environmental conditions such as backup for the EDGs. This is a The licensee explains that it did excessive heat loads, excessive electrical documentation issue that has no numerical consider environmental factors , but loads or excessive humidity that might lead to impact on the Internal Events PRA model. documentation remains to be updated.
SDG system failure. (Finding) This issue does not affect NFPA-805 Based on this explanation, the NRC change evaluations. staff finds the disposition of the F&O to be acceptable.
TH-01 The medium LOCA event tree analysis The numerical impact of this F&O on the RAI Not Needed assumes that upon failure of AFW, feed and Internal Events PRA results is judged very bleed is required, but success of AFW should small. Since no fire consequentially causes The licensee explains that the not be required and feed and bleed should be a Medium LOCA event, there is no effect of assumption cited in the F&O produces unnecessary. (Significance Level C) this F&O on NFPA-805 change evaluations only a small impact to on fire risk since no fire causes a consequential Medium (i.e., the same contribution occurs in both LOCA.
the before and after results).
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
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Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
TH-02 Modular Accident Analysis Program This issue relates specifically to the Internal RAI Not Needed (MAAP) runs evaluating containment Events PRA model. Since no fire overpressure timing for large LOCA obtained consequentially causes a Large LOCA Large LOCA is not a contributor to fire results that seemed overly conservative. The event, there is no effect of this F&O on risk.
success criteria documentation would be NFPA-805 change evaluations (i.e., the Based on this explanation, the NRC improved by providing hard copies of some same contribution occurs in both the before staff finds the disposition of the F&O to additional output (e.g., plots) of plant specific and after results). be acceptable.
analyses (MAAP runs, etc.); this would also improve the ability to evaluate not only the correctness of the conclusion, but also the reasonableness of the overall results.
(Significance Level C)
TH-03 There appears to be an inconsistency This is a documentation issue that has no RAI submitted as RAI 21(c) 1 between the current event trees and the numerical impact on the Internal Events success criteria notebook text. (Significance PRA model. This issue does not affect In response to RAI 21(c) the licensee Level D) NFPA-805 change evaluations. explains that the events trees and fault trees do implement the correct success criteria but the notebook needs updating.
Given the additional information, the NRC staff finds the disposition of the F&O to be acceptable.
TH-04 This is a suggestion for making the The fire PRA has performed separate RAI Not Needed bases for Heating Ventilation Air Conditioning evaluations for room heat-up and need for (HVAC) dependency modeling decisions HVAC. This issue does not affect NFPA- HVAC success and dependencies are clearer and more traceable. (Significance 805 change evaluations. separately evaluated for the fire PRA.
Level C)
Based on the explanation, the NRC 41
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) staff finds the disposition of the F&O to be acceptable.
TH-05 The Containment Equalization (CEQ) The numerical impact of this F&O on the RAI Not Needed fans are not included in the hydrogen control Internal Events PRA results is judged very evaluation for LERF estimation. (Significance small, since the overall failure probability of In the response to RAIs dated April 27, Level C) both trains of the CEQ fans is ~5E-4 and 2012, the licensee explains for this would increase the LERF conditional F&O that CEQ fans are not credited and that this represents conservative probabilities by less than 1% for non-SBO modeling.
and non-bypass scenarios. For fire-induced scenarios, the possibility of consequential Given the additional information, the failure increases the CEQ fan failure NRC staff finds the disposition of the probability. Assuming that at least one CEQ F&O to be acceptable.
fan train is available following any fire initiator, the conditional LERF probability would increase by ~0.01, or which is roughly 10% to 20%. Since fire initiators do not consequentially cause SBO or containment bypass scenarios, this increase in fire-related LERF is small relative to the overall LERF value. As a result, the effect of this F&O should not significantly affect NFPA-805 change evaluations.
TH-06 The basic success criteria based on The disposition for the Internal Events PRA RAI submitted as RAI 21(a) 1 MAAP analyses were developed in the model brought the affected Supporting 1991/1992 time frame. (Significance Level B) Requirement up to at least Capability In response to RAI 21(a) the licensee Category II. explains that modeling guidance was developed and implemented to passive 42
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response) failures in both the initiator and system response modeling to address this Level A finding.
Given the additional information, the NRC staff finds this deficiency has been appropriately resolved by the licensee.
TH-08 Unable to establish basis for the time The success criteria verification notebook RAI submitted as RAI 21(b) 1 available to actuate bleed and feed for explicitly states that the scenarios analyzed transients without steam conversion. for feed and bleed timing represented a In response to RAI 21(b) the licensee (Significance Level C) loss of main feedwater at the sequence explains that 92 new MAAP runs were initiation. The event timing provided in this made for the fire PRA to investigate timing given loss of AFW including time notebook show that the feed and bleed available for initiating for feed and HRA is based on a very conservative time bleed.
estimate for transients without steam conversion. The success criteria verification Given the additional information, the notebook was prepared subsequent to the NRC staff finds the disposition of the HRA to which the F&O refers. This F&O to be acceptable.
discussion shows that the F&O has no effect on the Internal Events PRA model, although the referenced HRA modeling is conservative. This issue does not affect NFPA-805 change evaluations.
TH-09 There is a reference in the Event Tree This is a documentation issue that has no RAI Not Needed notebook to NUREG-1335, and consideration numerical impact on the Internal Events should be given to changing this to a more PRA model. This issue does not affect This is a documentation issue.
current reference such as RG 1.174. NFPA-805 change evaluations. Documentation remains to be updated.
43
Record of Review D.C. Cook LAR Attachment U - Table U-1 Internal Events PRA Peer Review - Facts and Observations (F&Os)
NRC Staff Findings (Note 1: from April 27, 2012 RAI Facts and Observations (F&Os) Licensee Disposition Response)
(Significance Level C)
Based on this explanation, the NRC staff finds the disposition of the F&O to be acceptable.
44