ML14086A385

South Texas Project, Units 1 & 2 - Response to NRC Accident Dose Branch Request for Additional Information Regarding STP Risk-Informed GSI-191 Application

ML14086A385
Person / Time
Site:	South Texas
Issue date:	03/17/2014
From:	Powell G T South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML14086A383	List: ML14086A385 ML14086A386
References
GSI-191, NOC-AE-14003082, STI33816627, TAC MF2401, TAC MF2400
Download: ML14086A385 (8)

Text

Nuclear Operating Company.S'uli Tevas Ah ,fr'd r/lertri (7Cenemfi;So 7., PO. bS 2,59 W?&Wjh'ýn Tckxi 774,1JMarch 17, 2014NOC-AE-1400308210 CFR 50.1210 CFR 50.90U. S. Nuclear Regulatory CommissionAttention: Document Control DeskWashington, DC 20555-0001South Texas ProjectUnits 1 & 2Docket Nos. STN 50-498, STN 50-499Response to NRC Accident Dose Branch Request for Additional InformationRegarding STP Risk-Informed GSI-191 Application(TAC NOs MF2400 and MF2401)

References:

1. Letter, G. T. Powell, STPNOC, to NRC Document Control Desk, "Supplement 1 toRevised STP Pilot Submittal and Requests for Exemptions and License Amendment forRisk-Informed Approach to Resolving Generic Safety Issue (GSI)-191," November 13,2013, NOC-AE-13003043, ML13323A1832. Email, Andrea George, NRC, to Albon Harrison, STPNOC, "RAI's Regarding SouthTexas Project's Submittal for Risk-Informed Resolution of GS-191", January 14, 2014,ML14015A045This submittal responds to requests for additional information in Reference 2 with regard to theSTP Nuclear Operating Company (STPNOC) risk-informed application for the .resolution of GSI-191 (Reference 1).There are no regulatory commitments in this letter.T 66ST133816627.

NOC-AE-1 4003082Page 2 of 3If there are any questions, please contact Mr. Michael Murray at 361-972-8164.I declare under penalty of perjury that the foregoing is true and correct.Executed on: u t-1 zo-G. T. PowellSite Vice PresidentawhAttachments:1. Response to Accident Dose Branch Request for Additional Information2. Risk-Informed GSI-191 AADB RAI 3 Response3. Alternate Source Term Dose Analysis: An Estimate of Risk Attributed to GSI-191STP-RIGSI191-RAI.1 NOC-AE-1 4003082Page 3 of 3cc:(paper copy)(electronic copy)Regional Administrator, Region IVU. S. Nuclear Regulatory Commission1600 East Lamar BoulevardArlington, TX 76011-4511Balwant K. SingalSenior Project ManagerU.S. Nuclear Regulatory CommissionOne White Flint North (MS 8 B1)11555 Rockville PikeRockville, MD 20852NRC Resident InspectorU. S. Nuclear Regulatory CommissionP.O. Box 289, Mail Code: MN116Wadsworth, TX 77483Jim CollinsCity of AustinElectric Utility Department721 Barton Springs RoadAustin, TX 78704Steven P. Frantz, EsquireA. H. Gutterman, EsquireMorgan, Lewis & Bockius LLPBalwant K. SingalMichael MarkleyJohn StangU. S. Nuclear Regulatory CommissionJohn RaganChris O'HaraJim von SuskilNRG South Texas LPKevin PolioRichard PefiaL. D. BlaylockCity Public ServicePeter NemethCrain Caton & James, P.C.C. MeleCity of AustinRichard A. RatliffRobert FreeTexas Department of State Health Services NOC-AE-1 4003082Attachment 1Response to Accident Dose BranchRequest for Additional Information NOC-AE-1 4003082Attachment 1Page 1 of 4Risk Informed GSI-191 Accident Dose Branch (AADB) RAI ITo ensure a complete and accurate review of the dose consequence analyses, please provideadditional information in tabular form describing, for each design basis accident affected by theproposed Risk Informed GSI-191 submittal, all the basic parameters used in the doseconsequence analyses. For each parameter, please indicate the current licensing basis (CLB)value, the revised GSI-191 value where applicable, as well as the basis for any changes to theCLB. An example of the input/assumptions needed is provided in Table 4.3-11 "Dose AnalysisInputs for LOCA" provided in STP's alternate source term submittal [Agencywide DocumentsAccess Management System (ADAMS) Accession No. ML070890474]. The staff requests thatthe information provided include all of the basic parameters whether or not the individualparameter is being changed for the GSI-1 91 amendment. The staff also requests that theinformation be provided in separate tables for each affected accident (i.e., loss-of-coolantaccident (LOCA), the fuel handing accident (FHA), the main steam line break accident (MSLB),the steam generator tube rupture accident (SGTR), the control rod ejection accident (CREA),and the locked rotor accident (LRA)).STP Response:Other than to add a study calculation for the response to RAI 3 below, STPNOC did notrevise the licensing basis dose analyses, including the Alternate Source Term analyses,for the risk-informed GSI-1 91 licensing application. The analyses and results currentlydescribed in the STP UFSAR for the events identified above remain valid.Risk Informed GSI-191 AADB RAI 2STP identified the following condition related to the alternative source term (AST) licenseamendments currently in effect at STP Units 1 and 2. Westinghouse Electric Company NuclearSafety Advisory Letter (NSAL)-06-15, dated December 13, 2006, advised operators ofWestinghouse plants that the single-failure scenario for the SGTR analysis that licensees usedin their accident analysis may not be limiting. As stated in the STP AST NRC Safety Evaluationdated March 6, 2008 (ADAMS Accession No. ML080160013), "The licensee has evaluated theapplicability of NSAL-06-15 against the accident analysis assumptions and has determined thatthe current single-failure assumption for the STP SGTR analysis is not limiting. Therefore, thelicensee is operating under compensatory measures to meet regulatory dose guidelines. Thelicensee plans to resolve this condition at the earliest opportunity so that the assumptions,including the limiting single failure, for the SGTR accident analysis described herein areconsistent with the plant response to this event. To support the limiting single-failureassumptions in the SGTR analysis, STP will maintain an administrative limit for reactor coolantsystem (RCS) dose equivalent iodine 131 (DEI) so that the radiological dose reference valuesfor the SGTR analysis remain bounding, and the licensee will continue to comply with GDC 19."Has this condition been resolved? If so, how? Also, provide justification that GDC 19continues to be met.

NOC-AE-1 4003082Attachment 1Page 2 of 4STPNOC Response:The condition described in the RAI above was resolved by a design change to make thesteam valves to the moisture separator reheater fail closed. The design change hasbeen implemented in both STP units. This corrective action restored the original designand licensing basis and eliminated the need for the administrative limit on DEI that hadbeen implemented as a compensatory action. Condition Record 07-2887 details theresolution in accordance with the STPNOC Corrective Action Program.Restoration of the original design basis as described above maintains the originalcompliance with GDC 19 without need for compensatory action.STPNOC also addresses the relation between the risk-informed GSI-191 analyses andthe AST analyses with respect to compliance with GDC 19 in Section 2.2 of Enclosure 2-1 of Reference 1 to the cover letter.Risk Informed GSI-191 AADB RAI 3The LOCA analysis assumes that iodine will be removed from the containment atmosphere bycontainment spray and natural diffusion to the containment walls. As a result of these removalmechanisms a large fraction of the released activity will be deposited in the containment sump.The sump water will retain soluble gases and soluble fission products such as iodines andcesium, but not noble gases. The guidance from RG 1.183 specifies that the iodine deposited inthe sump water can be assumed to remain in solution as long as the containment sump pH ismaintained at or above 7.The AST application indicates:"After the first day, the containment sump pH will begin to decrease, reaching 6.8 by the end ofthe 30-day duration of the radiological consequence analysis for the DBA LOCA, and the impactof that decrease has been reflected in the Control Room and offsite doses."It is noted that the AST application further indicates:"The design inputs for calculating the containment sump pool pH were conservativelyestablished by the licensee to maximize the acidic contribution to sump pH and minimize thebasic contribution."The GSI-1 91 application indicates the possibility that debris generated during a LOCA couldclog the containment sump strainers in pressurized-water reactors (PWRs) and result in loss ofnet positive suction head (NPSH) for the ECCS and CSS pumps, impeding the flow of waterfrom the sump.Discuss the exemption justification as they relate to the effects on sump water pH, radiologicalconsequences, and loss of the containment spray system.

NOC-AE-1 4003082Attachment 1Page 3 of 4STPNOC Response:Enclosure 2-4 "Request for Exemption from General Design Criterion 41" of the licenseamendment, STPNOC addressed exemption from 10 CFR Part 50 Appendix A, GeneralDesign Criteria (GDC) 41, Criterion 41 -Containment atmosphere cleanup. STPNOC didnot revise the licensing basis dose analyses, including the Alternate Source Term (AST)analyses, for the risk-informed GSI-191 licensing application except to add a studycalculation for the response to this RAI. The analyses and results currently described inthe STP UFSAR for the events identified above remain valid.The licensing application is structured to show that the sumps are sufficiently reliable asa support function for CSS as currently licensed. STP has applied RG 1.174 to assessthe effects of debris using a risk-informed approach and shown acceptable results. Inorder to provide a risk-informed perspective on the sump design, the risk associated withGSI-191 is evaluated to include the failure mechanisms associated with sump blockageaffecting Containment Spray System (CSS) recirculation mode.In the risk-informed application, the sump pH history was investigated over 30 days bothanalytically and experimentally [1] (attached). The investigation shows the STP sump pHwill remain substantially above 7.0 for thirty days.Any loss of loss of net positive suction head (NPSH) for the Emergency Core CoolingSystem (ECCS) and Containment Spray System (CSS) pumps, impeding the flow ofwater from the sump has been analyzed using a risk-informed approach [2] (attached.)The risk-informed analysis assesses the impact of a GSI-191 related sump failure on theCSS and associated AST acceptance criteria. For breaks that result in sump blockageand which initially have two or more CSS trains available (consistent with single failure ofone CSS train, per the deterministic AST analysis), the analysis determines theexpected time that the CSS trains would operate before failing due to blockage. Thetime is then evaluated using the STP AST engineering calculation to determine thecontrol room and Technical Support Center dose. Finally the risk-informed analysisevaluates the fraction of the cases that would result in exceeding the AST acceptancecriteria.As shown in [2], Figure 1, sump clogging doesn't start until about 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. As shown inthe reference analysis [2], the risk for exceeding dose limits identified in RG 1.183 isacceptably low. Most events (-81%) result in dose within the AST limit, and the largestdose for the relatively small fraction of events (-19%) that do exceed the acceptancecriteria is less than 2 rem over the 5 rem limit and the probability is very low(-3.7E-09/yr). The table below is a summary of the AST analysis for dose after loss(CSS Cutoff) of two or more CSS pumps. As can be seen, the dose limits (10 CFR50.67 limits) at the Exclusion Area Boundary (EAB) and Low Population Zone (LPZ) willnot be challenged for early losses of CSS (see the tabulated values at 2.185 hours0.00214 days <br />0.0514 hours <br />3.058862e-4 weeks <br />7.03925e-5 months <br />).

NOC-AE-1 4003082Attachment 1Page 4 of 4Dose at CSS Cutoff Time(sum of results from Tables D3, D4, & D5 LB dose analysis)EAB LPZ CR TSC(REM)* (REM) (REM) (REM)10CFR50.67 Limit 25 25 5 5Design Basis 5.68 2.89 3.74 4.40CSS Cutoff @ 2.185 5.70 4.69 6.70 6.33hoursCSS Cutoff @ 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> 5.68 3.50 4.76 5.04CSS Cutoff @ 4.25 5.68 3.41 4.62 4.95hoursCSS Cutoff @ 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> 5.68 3.03 3.98 4.54CSS Cutoff @ 7.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> 5.68 2.96 3.87 4.47CSS Cutoff @ 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> 5.68 2.89 3.74 4.40l*#- dose is a worst 2-nour integratedvalues.value. All otner aoses are 30u day integratedAlso as described in Enclosure 4-1 to Reference 1 of the cover letter, realizing thesource term necessary to produce the doses as calculated in the dose assessment isunlikely based on the Regulatory Guide 1.174 evaluation that shows defense in depthand substantial safety margin.References (attached)[1] Risk-Informed GSI-191 AADB RAI 3 Response (Attachment 2 listed in cover letter)[2] Alternate Source Term Dose Analysis: An Estimate of Risk Attributed to GSI-1 91STP-RIGSI191-RAI.1 (Attachment 3 listed in cover letter)