NG-11-0135, Clarification of Information Contained in License Amendment Request (TSCR-120): Application for Technical Specification Change Re Risk-Informed Justification for Relocation of Specific Surveillance Frequency Requirements to Licensee.
| ML111110507 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 04/20/2011 |
| From: | Costanzo C NextEra Energy Duane Arnold |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NG-11-0135, TSCR-120, TSTF-425, Rev 3 | |
| Download: ML111110507 (8) | |
Text
NEXTera M ENERGY~
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DUANE ARNOLD April 20, 2011 NG-11-0135 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No. 50-331 Renewed Op. License No. DPR-49 Clarification of Information Contained in License Amendment Request (TSCR-120):
Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (TSTF-425, Rev. 3)
Reference:
License Amendment Request (TSCR-120): Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (TSTF-425, Rev. 3), NG-11-0037, dated February 23, 2011 In the referenced letter, NextEra Energy Duane Arnold, LLC (hereafter NextEra Energy Duane Arnold) requested a revision to the Technical Specifications (TS) for the Duane Arnold Energy Center (DAEC) pursuant to 10 CFR 50.90. Attachment 2 of that application contained a description of the Probabilistic Risk Assessment (PRA) model of the DAEC. The purpose of that description was to demonstrate the adequacy of the PRA model that will support the implementation of this TS change upon ---
approval by the Nuclear Regulatory Commission (NRC).
In a conference calion March 29, 2011, the NRC Staff requested that we clarify certain information in that attachment regarding the PRA model currently under development. The attachment to this letter contains the requested clarifications.
NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324
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Document Control Desk NG-11-0135 Page 2 of2 This clarification does not impact the 10 CFR 50.92 evaluation of "No Significant Hazards Consideration" previously provided in the referenced application.
This letter makes no new commitments or changes to any existing commitments.
If you have any questions or require additional information, please contact Steve Catron at 319-851-7234.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on April 20, 2011 Christopher R. Costanzo Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC
Attachment:
Clarification of DAEC PRA Model Description cc: M. Rasmusson (State of Iowa)
Attachment to NG-11-0135 Page 1 of 6 Request for Clarifying Information - NextEra Energy Duane Arnold Probabilistic Risk Assessment Model for Use in Implementing TSTF-425, Rev.1 During a teleconference held on March 29, 2011 between the NRC Staff and NextEra Energy Duane Arnold personnel, the Staff requested that information contained in of the referenced application (Documentation of PRA Technical Adequacy) be clarified to assist the Staff in evaluating the Duane Arnold Energy Center (DAEC)
Probabilistic Risk Assessment (PRA) model. Specifically, the following information was requested:
- 1) The application states that Revision 6 of the DAEC PRA, currently under development, will be the model used to implement this Technical Specification (TS) change upon approval. When is it expected to be finalized and issued for use?
Response
As stated in the application, Revision 6 is intended to also support the conversion of the DAEC Fire Plan to the NFPA-805 standard. As the license amendment request for the Fire Plan conversion is currently scheduled for submission by June 29, 2011, Revision 6 of the DAEC PRA will be implemented no later than that date.
- 2) The application discusses the results of the Peer Review conducted on the DAEC PRA model, Revision 5C. That review resulted in the identification of 83 potential gaps to meeting Capability Category II in the Supporting Requirements of the ASME Standard. However, the Tables provided in Attachment 2 of the submittal only discuss 30 of those items. Please provide a discussion of the disposition of all 83 identified items and the expected status of any open items when Revision 6 of the model is issued.
Response
The intent of the Attachment 2 Tables was to discuss only those items that remained in an open status at the time of the application and to bin them into separate Tables by significance. Therefore, any item which had already been dispositioned and closed in the Revision 6 model was not reported in the Tables because they no longer represented gaps to Capability Category II. Because Peer Reviews often result in findings that may represent potential gaps in more than one Supporting Requirement in the ASME Standard, there was overlap between the line items found in the 3 Tables in the application which makes a simple tallying of them back to the original 83 items difficult.
Subsequent to the original application, NextEra Energy performed a follow-up Focused Peer Review to validate the closure of those previously identified 83 items from the 2007 Peer Review. In addition, that review utilized the current version of the ASME Standard (RA-Sb-2009).
Attachment to NG-11-0135 Page 2 of 6 The Focused Peer Review team found that NextEra Energy had appropriately incorporated most of the 83 previously identified items into Revision 6. However, not all of the closures were found to fully meet Capability Category II requirements, which resulted in new open items, in addition to those items that remained open at the time of the Focused Peer Review. The final result was a total of 12 items that were assessed as not meeting Capability Category II per the current ASME Standard. Of these 12 items, five will be addressed and incorporated into Revision 6 of the DAEC model upon issuance prior to June 29, 2011. The remaining seven items are judged to have either no, or only minor, impact on the models ability to support this application. The following Table describes those seven open items.
In order to not repeat the confusion created by binning them into gaps, findings, and suggestions, as was done in the original Attachment 2 Tables, we have simplified the presentation of the current open items on the pending Revision 6 of the DAEC PRA model into a single Table.
Attachment to NG-11-0135 Page 3 of 6 ASME Category II SRs Not Met in DAEC Model, Rev. 6 ASME SRs Category II SR Details Description of GAP Impact on Quantification Importance to Application GROUP initiating events only when the Several findings and suggestions under HLRA and HLRB have been following can be assured: dispositioned/resolved, but the subsuming (IEB3) and screening (IEC4 (C6)) of initiating events does not meet the standard. The (a) events can be considered similar in following provides example summarizes (IE Notebook, including terms of plant response, success Appendix H):
criteria, timing, and the effect on the operability and performance of RBCCW (fails CRD, which is credited for early injection) is operators and relevant mitigating subsumed by TT, but RBCCW is not failed given TT.
systems; or Modeling these additional initiators will GSW (fails RBCCW, CRD, Feedwater, etc.) is subsumed by TC, but better define certain accident sequences Although the importance of affected these systems are not failed given TC.
and a more accurately determine components is not fully considered; (b) events can be subsumed into a group The impacts of Reference and Variable Leg Breaks are not associated SSC importance. their impact can be addressed for and bounded by the worst case impacts adequately described and are subsumed by Loss of FW. Most specific 5b applications using IEB301A within the "new" group. likely would be a manual shutdown with complications verses a Overall calculated risk slightly increase; sensitivity analysis, qualitative Loss of FW. Given that immediate shutdown would occur given a significantly for specific functions analysis, bounding analysis or AVOID subsuming events into a group break, these should be modeled. Section 2.4.8 described the low associated with the initiating event. Some explicit modeling in accordance with unless: risk from these, but this does not meet standard for screening.
applications may see a slight decrease in the NEI 0410 guidance.
1A1/1A2 bus failures and partial loss of feedwater (one pump) are (i) the impacts are comparable to or less binned to TT, but this impact is not modeled given TT. risk margin.
than those of the remaining events in 1A3/1A4 bus failures are subsumed with TT. Impact on loss of that group, chargers [TS 3.8.4.] etc. and possibility that failure is a problem could lead to an immediate shutdown. Notes 11 and 12 suggest AND that only normal power source is lost, but emergency power is also unavailable if bus fails.
(ii) it is demonstrated that such grouping does not impact significant accident RECOMMENDATION: Follow IEB3 and C6 with regard to subsuming sequences. and screening or more importantly model the above initiating events.
The SBO event tree does not take credit for containment venting Crediting the B5b procedure that Will improve results for 5b using an alternate alignment when the pneumatic supply is lost. DAEC implements containment venting without a applications especially those procedure SAMP 706 provides detailed direction for venting PC given pneumatic supply will reduce overall functions associated with SBO.
INCLUDE the effects of both normal and an unavailable pneumatic supply. The Containment Vent notebook calculated risk. Will have a more significant SYA501A alternate system alignments, to the extent does not credit/discuss this procedure. impact on SBO sequences.
Without this change the model is needed for CDF and LERF determination.
conservative.
RECOMMENDATION: Add containment venting to the event tree along with operator actions and component alignments needed to vent containment without the pneumatic supply system.
Attachment to NG-11-0135 Page 4 of 6 ASME Category II SRs Not Met in DAEC Model, Rev. 6 ASME SRs Category II SR Details Description of GAP Impact on Quantification Importance to Application There is no Fire Water System (Alternate Injection) notebook or Documenting the use of the fire water Will improve results for 5b DOCUMENT the system functions and equivalent information in another notebook. The operator action to system as an alternate injection source will applications especially those boundary, the associated success criteria, align fire water for injection is modeled but the components are facilitate a more thorough evaluation of functions associated with SBO.
the modeled components and failure based on the argument that the probability of the action subsumes this function. Crediting fire water injection modes including human actions, and a the component failure rates.
SYC201A (late in the event) will decrease overall risk, Without this change the model is description of modeled dependencies especially for SBO sequences. conservative.
including support system and common RECOMMENDATION: Develop new system notebook for use of fire cause failures, including the inputs, water as an alternate injection source.
methods, and results.
HRA Notebook (Appendix J, Table J1) includes a systematic approach No impact. As noted by the review team a No impact since DAEC staff did to identifying test and maintenance activities through a system by systematic approach was used to identify review all procedures; however they system review of potential misalignments. This meets the high level potentially significant misalignments. did not document this review.
requirement to use a systematic approach and is judged to be Based on this review, only the procedures For equipment modeled in the PRA, adequate by the Peer Review team. However, the SR wording that were associated with these alignments IDENTIFY, through a review of procedures requires a review of procedures and practices which was not were reviewed further. DAEC noted that and practices, those test and maintenance followed. As a result, the PR team must assess this SR as not met. they did review all the procedures but did HRA101A activities that require realignment of not document this review.
equipment outside its normal operational RECOMMENDATION: Reassess this SR when the Addendum B of the or standby status. PRA Standard is released. The current proposed revision deletes the requirement for a review of procedures and practices. The draft revision of addendum B to HRA1 that is currently in review deletes the requirement for a review of procedures and practices.
HRA Notebook (Appendix J, Table J1) includes a systematic approach No impact. As noted by the review team a No impact since DAEC staff did to identifying calibration activities through a system by system review systematic approach was used to identify review all procedures; however they of potential miscalibrations. This meets the high level requirement to potentially significant miscalibrations. did not document this review.
use a systematic approach and is judged to be adequate by the Peer Based on this review, only the procedures Review team. However, the SR wording requires through a review of associated with these acions were reviewed IDENTIFY, through a review of procedures procedures and practices which was not followed. As a result, the PR further. DAEC noted that they did review and practices, those calibration activities team must assess this SR as not met. all the procedures but did not document HRA201A that if performed incorrectly can have an this review.
adverse impact on the automatic initiation RECOMMENDATION: Reassess this SR when the Addendum B of the of standby safety equipment.
PRA Standard is released. The current proposed revision deletes the requirement for a review of procedures and practices. The draft revision of addendum B to HRA1 that is currently in review deletes the requirement for a review of procedures and practices.
Attachment to NG-11-0135 Page 5 of 6 ASME Category II SRs Not Met in DAEC Model, Rev. 6 ASME SRs Category II SR Details Description of GAP Impact on Quantification Importance to Application A number of preIE HFEs are identified for modeling in the PRA. Roughly 10 preinitiators are affected. The May have a minor impact on some Generally these HFEs are at the train or system level, as appropriate. probability for these preinitiators is low. 5b applications.
However, a small set were identified at the system level without Therefore addressing this finding is related trainlevel HFEs. It is possible that the train level HFE may be expected to have a minor impact on overall important to system unavailability. For example, miscalibration of DG risk.
For each unscreened activity, DEFINE a fuel oil level transmitters is done at the system level, but not at the human failure event (HFE) that represents train level. At the train level, the HFE would be 8e3, compared with HRC101A the impact of the human failure at the independent failure of the level transmitter of 5e4. In other cases, appropriate level, i.e., function, system, the HFE is at the train level, but no corresponding system level train, or component affected. dependent HFE is included. For example, failure to restore RHR SW post TM is developed at the train level, but no common misalignment of both trains is considered.
RECOMMENDATION: Review the differences between the modeling of system impact vs train.
Category I was met. Adding initiating event Although the importance of affected IDENTIFY significant contributors to CDF, RECOMMENDATION: Fault trees are required for support system fault trees will not alter overall results if the SSCs on an initiating event may not such as initiating events, accident initiating events in order to satisfy this SR [Cat II]. fault tree results are in agreement with the be fully considered; their impact can sequences, equipment failures, common original point estimates. However there be addressed for specific 5b QUD5a01A cause failures, and operator errors [Cat I]. will be an increase in risk importance applications using sensitivity INCLUDE SSCs and operator actions that associated with operator actions and SSCs analysis, qualitative analysis, contribute to initiating event frequencies that are included in the initiating event bounding analysis or explicit and event mitigation [Cat II]. fault trees. modeling in accordance with the NEI 0410 guidance.
Attachment to NG-11-0135 Page 6 of 6 These open items are contained in a controlled database that, by NextEra Energy procedure, must be reviewed prior to beginning any PRA application. Therefore, each open item will be reviewed as part of the Surveillance Test Interval change assessment.
If an open item has a potential impact on the results, then additional assessments (sensitivities) will be performed in accordance with the guidance contained in NEI 04-10.
In summary, with the exception of the seven items listed in the above Table, all previously identified items that represent gaps to Capability Category II will be fully incorporated into Revision 6 of the DAEC PRA model upon formal issuance.