RS-10-084, Additional Information Supporting Application for Technical Specification Change Regarding Risk-Informed Justification for Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program
| ML101160374 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 04/26/2010 |
| From: | Simpson P Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-10-084 | |
| Download: ML101160374 (13) | |
Text
Exelon Generation www.exeloncorp.com 4300 W~nfield Road Nuclear April 26, 2010 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374
Subject:
Additional Information Supporting Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program
Reference:
Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (Adoption of TSTF-425, Revision 3j," dated February 15, 2010 In the referenced letter, Exelon Generation Company, LLC (EGC) requested an amendment to Facility Operating License Nos. NPF-11 and NPF-18 for LaSalle County Station (LSCS), Units 1 and 2, respectively. The proposed change modifies the LSCS Technical Specifications (TS) by relocating specific surveillance frequencies to a licensee-controlled program. Attachment 2 of the referenced letter provided documentation with regard to probabilistic risk assessment (PRA) technical adequacy. Table A.2-1, "LaSalle PRA 2008 Peer Review Results," included information regarding the gaps that were identified during the peer review cf the LSCS PRA.
During a conference call with the NRC on April 15, 2010, the NRC indicated that with respect to Table A.2-1, a more detailed discussion of the identified gaps was needed, rather than the associated supporting requirement descriptions. As a result, EGC is providing a revised version of Table A.2-1 that includes a discussion of the gaps identified during the peer review.
EGC has reviewed the information supporting a finding of no significant hazards consideration, and the environmental consideration, that were previously provided to the NRC in Attachments 6 and 1, respectively, of the referenced letter. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the additional information provided in this submittal does not affect the bases for concluding that neither an environmental impact
April 26, 201 0 U.S. Nuclear Regulatory Commission Page 2 statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Kenneth M. Nicely at (630) 657-2803.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 26th day of April 201 0.
Manager - Licensing 84
Attachment:
Additional Information Supporting Probabilistic Risk Assessment Technical Adequacy cc:
NRC Regional Administrator, Region lii NRC Senior Resident Inspector --- LaSalle County Station Illinois Emergency Management Agency - Division of Nuclear Safety
ATTACHMENT Additional Informa1:ion Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS SUPPORTING IE-A7 Although a detailed plant-specific precursor review was not reported, industry wide initiating evlent precursors are considered and documented where appropriate in the LaSalle initiating event (IE) analysis (e.g., loss of station cooling, ISLOCA, loss of multiple DC buses, reference leg brea~k, and the various LOCA categories).
Additionally, plant-specific precursors i ~ e specifically considered in the plant water intake evalual.ion provided in Appendix G.l of the component data notebooli.
IA jump from Category I to Category Ill could be achieved by
]supplementing the initiating event identification process with additional
]documented evidence that plant-specific operating experience
]precursors were considered (perhaps with reference to operations landlor system manager interviews that considered near misses, or IE-D3 The LS-PSA-013 notebook discusses the industry '%ey sources of uncertainty" per Electric Power Research Institute (EPRI) guidance.
However, the current analysis does not fully meet tile requirements of Regulatory Guide (RG) 1.200, which requires a discussion of sources
/of model uncertainty and related assumptions. Also, there may be
]some piant-specifi&assurnptions made that may not be fully captured I by the generic list of potential sources of uncertainty.
ASSESSMENT IMPACT ON BASE PRA Supporting Documentation issue. No impact.
Requirement Met No additional IE categories would Capability be identified. Peer reviewers Category (CC) I. desired greater discussionldocumentation of IE precursors.
Supporting Refer to the impact discussion for Requirement Not I Supporting Requirement QU-E4.
Met.
Expand the existing treatrnent of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assc~mptions that should also be noted as stources of uncertainty. NUREG-1855 and an upcoming EPRI Treatment of Uncertainty report should provide more guidance on how to meet this supporti~~g requirement (SR) in the future.
ATTACHMENT Additional 1nformat:ion Suppol-ting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS OF GAP P
a the industry '"key sources of ver, the current analysis does
.200, which requires a discussion of sources of rnodel uncertainty and related assumptions.
Also, there may be some plant-specific assumptions made that may not be fully captured by the generic lisi of potential sources of Expand the existing treatrnent of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assumptions that should also be noted as sources of uncertainty. NLJREG-1855 and an upcoming EPRI Treatment of Uncertainty report should provide more guidance on how to meet this SR in the future.
While the LS-PSA-003 notebook provides some selected comparison of RMIEP MELCOR results to more recent MAAP runs, there is no documented comparison of how the LaSalle success criteria compare to those used for sister plants or other similar comparisons as required for this SR. However, the success criteria used for LaSalle appear to be consistent with those of other similar boiling water reactors (BWRs).
The LS-PSA-003 docume!ntation should be enhanced to include a section that compares the LaSalle success criteria.to those used in the PRAs of other similar BWRs.
Supporting Requirement No1 Met.
Documentation issue. No impact.
The LaSalle PRA Success Criteria Notebook compares MAAP and MELCOR runs. The peer review team desired more comparisons with other plants and other codes.
ATTACHMENT Additional 1nformal:ion Supporting Probabilistic Risk Assessment Technical Adequacy Expand the existing treatrnent of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assumptions that should also be noted as sources of uncertainty. NUREG-1855 and an upcoming EPRl Treatment of Uncertainty report should provide more guidance on how to meet this SR in the future.
TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS DESCRIPTION The LS-PSA-(413 notebook discusses uncertainty" per EPRl guidanc not fully meet the requirernent discussion of sources of rnodel uncertainty and related assumptions.
Also, there may be some plant-specific assumptions made that may not be fully captured by the generic list of potential sources of uncertainty.
system engineer interviews are docunlented in the respective system notebooks. Operator interviews are documented in the Human Reliability Analysis (HRA) notebook. Each system notebook contains an appendix documenting interviews with system managers, however, there is little mention, if any at all, of walkdowns pel-formed in support of the system analyses. The impression received is that walkdowns were performed some time ago for a niuch earlier revision but have not been retained in the system notebooks.
Interview with plant engineers has been documented. However, plant walkdown details are not provided in the Standby Liquid Control, Core Standby Cooling, High Pressure Core Spray, and Reactor Core Isolation Cooling system notebooks.
7 Supporting Requirement Met (CC 1)
Documentation issue. No impact.
The majority of the LaSalle PRA System Notebooks include documented Operator Interviews and Walkdowns. The peer review team desired that every System Notebook include such documentation and that walkdowns be performed with both Ops and Systems personnel on the walkdown.
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ATTACHMENT Additional Information Suppo~ting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS discusses the industry '
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ATTACHMENT Additional 1nforrnat:ion Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS SUPPORTING I REQUIREMENTS DESCRIPTION OF GAP ASSESSMENT I PEER I
IMPACT ON BASE PRA Table 5.1-2 summarizes the post-initiator HEPs in tabular form, but no consistency check is discussed in the analysis.
The final HEP values need to be compared against each other to check their reasonableness. Table 5.1i-2 appears to have assembled for this purpose, but the ainalysis contains no discussion of any such consistency check.
The LS-PSA-013 notebook discusses the industry "key sources of uncertainty" per EPRl guidance. However, the current analysis does not fully meet the requirements of RG 1.200, which requires a discussion of sources of rnodel uncertainty and related assumptions.
Also, there may be some plant-specific assumptions made that may not be fully captured by the generic list of potential sources of uncertainty.
Expand the existing treatment of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assi~mptions that should also be noted as sources of uncertainty. NUREG-1855 and an upcoming EPRI Treatment OF Uncertainty report should provide more guidance on how to meet this SR in the future.
Supporting Requirement Not Met Supporting Requirement Not Documentation issue. No impact.
The EGC HRA best practices direct 1 performance of a reasonableness and this was performed for PRA. Peer Review team desired to see a detailed discussion of the reasonableness Met.
Refer to impact discussion for Supporting Requirement QU-E4.
DA-C8 Basic events used to model the standby status of various plant systems use a mixture of plant-specific operational data and engineering judgment. For the plant S'ervice Water system and several other systems, standby estimaites have been determined from procedures and operating data (see Appendix G of LS-PSA-010). For other components, assunlptions are used (e.g., 50% probability of either of two pumps in a system is in standby). So, overall LaSalle has some Category II attributes and some Category I attributes.
Collect plant-specific data for all of the basic events that reflect standby status to meet C,ategory I1 requirements.
Supporting Nan-significant impact. The LaSalk Requirement Met PRA uses primarily plant-specific (CC I).
information for configuration probabilities. Peer Review team desired that glJ configuration probabilities used in the PRA be based on plant-specific data.
ATTACHMENT Additional Information Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS fSCRlPTlONi OF GAP
--- d l ~ h e documentation should describe how tests were counted to fully meet the requirements of this SR.
The LS-PSA-013 notebook discusses.the industry '"ey sources of uncertainty" per EPRl guidance. However, the current analysis does not fully meet the requirements of RG 1.200, which requires a discussion of sources of rnodel uncertainty and related assumptions.
Also, there may be some plant-specific: assumptions made that may not be fully captured by the generic lisi of potential sources of uncertainty.
Expand the existing treatment of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assumptions that should also be noted as sources of uncertainty. NlJREG-1855 and an upcoming EPRl Treatment of Uncertainty report should provide more guidance on how to meet this SR in the future.
Supporting Requirement Not Met.
to impact discussion for Supporting Requirement QU-E4.
IF-C3b Appendix D addresses flow through drain lines (e.g., 314 and 3J5) and addresses doors as well. RG 1.200 appends the Category II requirements to include the potential for barrier unavailability, including maintenance. Barrier unavailability does not appear to have been discussed; however, given the nature of the major flooding scenarios it will probably make little difference.
In order to meet the Category II requirements of RC; 1.200 one must address potential unavailability of barriers that affect the propagation oi water.
Supporting Documentation issue. No impact.
Requirement Met Flood barrier unavailability is (CC I).
considered and including in the internal flood analysis. Peer review team desired to see more extensive discussions on this topic; however, the team expected any resulting changes to the model results would be non-significant.
SUPPORTING REQUIREMENTS a
IF-F3 ATTACHMENT Additional Informa1:ion Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-I LASALLE PRA 2008 PEER REVIEW RESULTS DtfSCRlPTlON OF GAP
. \\ -
The LS-PSA-013 notebook discusses.the industry 'key sources of uncertainty" per EPRl guidance. However, the current analysis does not fully meet the requirements of RG 1.200, which requires a discussion of sources of rnodel uncertainty and related assumptions.
Also, there may be some plant-specific assumptions made that may not be fully captured by the generic list of potential sources of uncertainty.
Expand the existing treatment of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific ass~imptions that should also be noted as s,ources of uncertainty. NCJREG-1855 and an upcoming EPRl Treatment of Uncertainty report should provide more auidance on how to meet this SR in the future.
PEER REVIEW ASSESSMENT Supporting Requirement Not Met.
IMPACT ON BASE PRA Refer to impact discussion for Supporting Requirement QU-E4.
QU-Dla ER-AA-600-1015 Attachment 2, "Review of Updated PRA Model,"
contains specific guidance for reviewing a sample of accident sequences/culsets to determine that the logic of the cutset or sequence is correct. Sections 6.3.1 and 6.5 of LS-13SA-014 discuss the top 10 core damage frequency (CDF) and large early release frequency (LERF) cutsets, respectively. The model appears to be reasonable based on these discussions. However, the top 10 CDF cutsets represent only about 31 % of the total CDF. The review team felt that additional cutsets, representing more % of the total CDF should be reviewed and cliscussed.
Supporting Requirement Not Met.
~ocumentation issue. No impact.
Cutset review is performed as part of the PRA update quantification and documentation process. Peer review team desired to see greater documentation of such a review.
In response to a query from the review team, the LaSalle PRA team stated that additional cutsets were reviewed, but were not documented. The PRA team should provide evidence that such a review was performed by documenting it in the Quantification
ATTACHMENT Additional Informat.ion Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS SUPPORTING REQUIREMENTS DEiSCRIPTION OF GAP QU-D4 ER-AA-600-1015 Attachment 2, "Review of Updated PRA Model,"
contains specific guidance for reviewing a sample of accident sequences/cutsets to determine that the logic of the cutset or sequence is correct.
Section 2 of LS-PSA-014 Quantification Notebook documents a review of top 10 cutsets; however, there is no documentation of a review of non-significant cutsets.
In response to a query from the review team, the LaSalle PRA team stated that additional non-significant cutsets were reviewed, but were not documented. The PR.A team should provide evidence that such a review was performed by documenting it in the Quantification Notebook.
The Summary Notebook includes documentation of key sources of uncertainty; however, with the changes to eliminate "key" from the SR definition, this SR cannot be considered met.
Expand the existing treatrnent of sources of uncertainty to consider sources of model uncertainty and related assumptions. Consideration should also be given to potential plant-specific assumptions that should also be noted as sources of uncertainty. NUREG-1855 and an upcoming EPRl Treatment of Uncertainty report should provide more guidance on how to meet this SR in the future.
a Refer to impact discussion for Supporting Requirement QU-E4.
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ATTACHMENT Additional Information Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-I LASALLE PRA 2008 PEER REVIEW RESULTS model is affected (e.g., introduction of a new basic event, changes to basic event probabilities, change in success criterion, introduction of a new initiating event)." Given that the requirements QU-E2 have not been met, this SR is consequently not met.
The changes to this SR as identified by the NRC via a Federal Register Notice in July 2007 indicate that for all sources of uncertainty, respectively, identify how the PRA model is affected.
Once items for QU-El and QU-E2 are identified per the new requirements, identify how the PRA model is affected (e.g. introduction of a new basic event, changes to basic event probabilities, change in success criterion, introduction of a new initiating event) for each item.
A detailed description of accident sequences is provided for the top 10 accident sequences which equates to -70% of the CDF. To meet this SR, a detailed description of significant accident sequences is required. Since no definition of significant is provided in QU-F6, then a detailed description for up to 95% of the accident sequences is required to meet this SR.
Provide a detailed description for the remaining accident sequences that comprise up to 95% of the CDF. Note that providing this information would also s~~pport meeting SR QU-Dla.
PEER REV'EW I lMPACT ON BASE PRA ASSESSMENT Supporting The LaSalle PRA Summary Requirement Not Notebook provides an extensive Met.
discussion of both parametric and modeling uncertainty and sensitivity studies for the base PRA.
Supporting Requirement Met (CC I).
The peer reviewers assessed the sources of uncertainty as not met in anticipation of the NUREG-I855
[Reference 101 and EPRl 101 6737
[Reference I I ] specific process yet to be issued at the time of review.
The LaSalle uncertainty and sensitivity discussions in the base PKA are judged to be consistent with, or exceed the recently issued NUREG-1 855 guidance; however, each ST1 change assessment will follow the NUREG-1855 construct.
Documentation issue. No impact.
Such information is documented in the PRA Quantification Notebook.
Peer review team desired to see more detailed documentation.
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ATTACHMENT Additional lnformaltion Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS that the requirements QU-E4 have not been met, this SR is consequently not met.
cumentation issue. No impact.
SR is not met.
Document the quantitative definition used for significant basic event,
)k discusses the industry '
fer to impact discussion for Page 10
ATTACHMENT Additional Information Supporting Probabilistic Risk Assessment Technical Adequacy TABLE A.2-1 LASALLE PRA 2008 PEER REVIEW RESULTS (ASME) standard for the significant sequence is most likely used in the LaSalle LERF analysis. tiowever, the fact that this definition may be used is not documented in the notebooks.
I Document the definition in the Level 2 notebook for significant accident progression sequence (also refer to QU-F6)
ASSESSMENT Supporting Requirement Not Met.
IMPACT ON BASE PRA Documentation issue. No impact.
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