ML13010A016

Browns Ferry Nuclear Plant, Unit 1, 10 CFR 50.46 30-Day Report

ML13010A016
Person / Time
Site:	Browns Ferry
Issue date:	01/04/2013
From:	Shea J W Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME3775
Download: ML13010A016 (6)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402January 4, 201310 CFR 50.410 CFR 50.46ATTN: Document Control DeskU.S. Nuclear Regulatory CommissionWashington, D.C. 20555-0001Browns Ferry Nuclear Plant, Unit 1Facility Operating License No DPR-33NRC Docket No 50-259Subject: 10 CFR 50.46 30-Day Report for Browns Ferry Nuclear Plant, Unit 1Reference: 1. TVA Letter to NRC, "10 CFR 50.46 Annual Report for Browns FerryNuclear Plant, Unit 1," dated April 30, 20122. NRC Letter, "Browns Ferry Nuclear Plant, Unit 1 -Issuance ofAmendments Regarding the Transition to AREVA Fuel (TAC No.ME3775) (TS-473)," April 27, 2012The purpose of this letter is to provide a 30-day report as required by Title 10 of the Code ofFederal Regulations (10 CFR) 50.46 of significant changes in the Emergency Core CoolingSystem (ECCS) evaluation model for Browns Ferry Nuclear Plant (BFN), Unit 1. Inaccordance with 10 CFR 50.46, "Acceptance Criteria for ECCS for Light-Water NuclearPower Reactors," paragraph (a)(3)(ii), the enclosure to this letter describes the nature andthe estimated effect on the limiting ECCS analysis of changes or errors discovered sincesubmittal of the 10 CFR 50.46 Annual Report for BFN, Unit 1 dated April 30, 2012(Reference 1).During the BFN, Unit 1, Fall 2012 refueling outage, modifications were completed thatrestored the automatic initiation capability of the BFN, Unit 1, Automatic DepressurizationSystem. As a result, NEDC-32484P Revision 6, "Browns Ferry Nuclear Plant Units 1, 2, and3: SAFER/GESTR-LOCA Loss-of-Coolant Accident Analysis," GE Nuclear Energy,February 2005 was re-established as the Loss of Coolant Accident (LOCA) analysis ofrecord for GE14 fuel, with a baseline peak cladding temperature (PCT) of 1760°F for GE14Printed on recycled paper U.S. Nuclear Regulatory CommissionPage 2January 4, 2013fuel. The previous baseline PCT reported in the Reference 1 letter was 1920°F for GE14fuel.AREVA ATRIUM-10 fuel was introduced into BFN, Unit 1 reactor core during the Fall 2012refueling outage. Reference 2 documents the NRC approval of the LOCA analysis forATRIUM-10 fuel for BFN, Unit 1 which includes the application of a modifiedEXEM BWR-2000 LOCA methodology. This analysis is established as the LOCA analysis ofrecord for ATRIUM-10 fuel with a baseline PCT of 1926°F for ATRIUM-10 fuel.In accordance with the BFN, Unit 1, Renewed Operating License and TechnicalSpecifications, the new baseline PCT values described above became effective onDecember 5, 2012. The 160'F change in the baseline PCT for GE14 fuel meets the criteriaof 10 CFR 50.46 (a)(3)(i) as a significant change. As such, in accordance with 10 CFR50.46 (a)(3)(ii), this 30-day report is required to be submitted by January 4, 2013.There are no new regulatory commitments in this letter. Please direct questions concerningthis issue to Tom Hess at (423) 751-3487.Respellly,JSSheaPresident, Nuclear Licensing

Enclosure:

10 CFR 50.46 30-Day Report for Browns Ferry Nuclear Plant, Unit 1cc (w/Enclosure):NRC Regional Administrator- Region IINRC Senior Resident Inspector -Browns Ferry Nuclear Plant ENCLOSURE10 CFR 50.46 30-DAY REPORTFORBROWNS FERRY NUCLEAR PLANT, UNIT IThe Browns Ferry Nuclear Plant (BFN), Unit 1, reactor core contains both the ATRIUM-1 0 andGE14 fuel designs. This report establishes new baseline peak cladding temperature (PCT)values for both fuel types, as described below.ATRIUM-10 Fuel EvaluationAREVA ATRIUM-10 fuel was introduced into the BFN, Unit 1 reactor core during the Fall 2012refueling outage. References 1 and 2 constitute the Loss of Coolant Accident (LOCA) analysisof record for ATRIUM-1 0 fuel in the BFN, Unit 1, reactor core. These analyses were reviewedby the NRC and approved for application to BFN, Unit 1, in Reference 3. The baseline PCT forATRIUM-10 fuel is 1926 'F.On June 28, 2012, AREVA notified the Tennessee Valley Authority (TVA) of a change to theirevaluation of thermal conductivity degradation over the approved burnup range. When oldergeneration codes, like AREVA's RODEX2 were approved, experimental data was not availableto support explicit modeling of thermal conductivity degradation with fuel burnup. However, inrecent evaluations of this phenomenon, it appears that the use of the RODEX2 code (whichprovides inputs to RELAX and HUXY in the LOCA analysis methodology) results inconservatively high temperatures at low burnup (less than 15 Giga-Watt Day per Metric TonUranium), but underpredicts pellet temperatures at higher exposures.For BFN, Unit 1, the current analysis (Reference 2) shows that the limiting PCT occurs atbeginning of life (BOL). As discussed in Reference 4, the effects of thermal conductivitydegradation at higher burnups result in a zero degree change in the limiting PCT, which occursat BOL. Therefore, there is no change in the reported PCT due to thermal conductivitydegradation for BFN, Unit 1.Table 1 details the accumulated PCT impact due to errors and changes in the ATRIUM-10LOCA analyses since the References 1 and 2 analyses of record.Table 1: Cumulative Effect of PCT Changes -BFN, Unit I (ATRIUM-10)Baseline PCT 1926 OFThermal Conductivity Degradation (Reference 4) + 0 OFAccumulated changes since baseline analysis 0 OFNew licensing PCT 1926 OFAbsolute value of accumulated changes 0 OFEnclosure -1 of 4 ENCLOSURE10 CFR 50.46 30-DAY REPORTFORBROWNS FERRY NUCLEAR PLANT, UNIT 1GE14 Fuel EvaluationDuring the BFN, Unit 1, Fall 2012 refueling outage, modifications were completed that restoredthe automatic initiation capability of the BFN, Unit 1, Automatic Depressurization System. As aresult, Reference 5 was re-established as the LOCA analysis of record for GE14 fuel, with abaseline PCT of 1760 OF. The applicability of this analysis to the as-modified plant configurationwas confirmed by GE-Hitachi in Reference 6. Reference 5 provides PCT results for bothExtended Power Uprate (EPU) and Current Licensed Thermal Power (CLTP) conditions. TheTVA has elected to use the CLTP results for 10 CFR 50.46 reporting, since EPU has not beenapproved for BFN, Unit 1, and all GE14 fuel is scheduled to be discharged from the reactor coreprior to the planned EPU implementation date.In addition, GE-Hitachi has provided three 10 CFR 50.46 error reports that are applicable to thelimiting BFN LOCA analysis for GE14 fuel.On July 20, 2011, GE-Hitachi issued 10 CFR 50.46 Notification Letter 2011-02 (Reference 7),which notified TVA of a database error that affected input coefficients used to direct thedeposition of gamma radiation energy produced by fuel when determining whether this energywould heat the fuel rod, cladding, channel, or control rod structure materials. The input causedthe heat deposited in the fuel channel (post scram) to be over predicted and the correspondingheat to the fuel to be under predicted. This effect was determined to be non-conservative. Theerror only applies to 10x10 fuel and increased the PCT by 25 °F. As discussed in Reference 6,this error is applicable to the current BFN LOCA analysis for GE14 fuel.On July 20, 2011, GE-Hitachi also issued 10 CFR 50.46 Notification Letter 2011-03 (Reference8), which notified TVA of an updated formulation for gamma heat deposition in the channel wallfor 9x9 and 1 0x1 0 fuel assemblies. An examination of the existing formulation revealed that thecontribution of heat from gamma ray absorption by the channel was found to have beenminimized. The method had been simplified such that initially all the energy was assumed to bedeposited in the fuel rods prior to the LOCA and then adjusted such that the correct heatdeposition was applied after the scram. This modeling was concluded to be potentially non-conservative, as not accounting for this small fraction of total power generation outside the fuelrod would tend to suppress the hot bundle power required to meet the initial operating AveragePlanar Linear Heat Generation Rate limit. Further, there is a small effect on the initial conditionsfor the balance of the core, as these are set in relation to the hot bundle condition. The energydistribution during the pre-scram phase was updated with the appropriate energy distribution.Since the integral heat deposition is dominated by post-scram energy, the change has only asmall impact on the results, increasing PCT by 15 OF. As discussed in Reference 6, this error isapplicable to the current BFN LOCA analysis for GE14 fuel.On November 29, 2012, GE Hitachi issued 10 CFR 50.46 Notification Letter 2012-01(Reference 9), which notified TVA of a change to the Emergency Core Cooling System (ECCS)evaluation model in response to NRC Information Notice 2011-21, "Realistic Emergency CoreCooling System Evaluation Model Effects Resulting from Nuclear Fuel Thermal ConductivityDegradation," and addressed inaccuracies in fuel pellet thermal conductivity as a function ofexposure. The PRIME fuel rod thermal-mechanical code addresses these thermal conductivityconcerns. Reference 9 estimates the magnitude of the change in PCT due to the change in fuelEnclosure -2 of 4 ENCLOSURE10 CFR 50.46 30-DAY REPORTFORBROWNS FERRY NUCLEAR PLANT, UNIT Iproperties in PRIME relative to the existing GESTR model used in Reference 5. The mostdominant effect of the PRIME fuel properties is in thermal conductivity, which results in a higherfuel stored energy. The impact of PRIME is drawn from stored energy sensitivity results. ForBFN, Unit 1, GE14 fuel, the PCT impact of modeling fuel rod mechanical properties with PRIMEwas determined to be zero degrees.Table 2 details the accumulated PCT impact due to errors and changes in the GE14 LOCAanalyses since the Reference 5 analysis of record.Table 2: Cumulative Effect of PCT Changes -BFN, Unit I (GE14)Baseline PCT 1760 OFInput coefficient database error 25 OFRevised gamma heat deposition formulation 15 OFPellet thermal conductivity degradation 0 OFAccumulated changes since baseline analysis 40 OFNew licensing PCT 1800 OFAbsolute value of accumulated changes 40 OFEnclosure -3 of 4 ENCLOSURE10 CFR 50.46 30-DAY REPORTFORBROWNS FERRY NUCLEAR PLANT, UNIT IReferences1. ANP-3015(P) Revision 0, "Browns Ferry Units 1, 2, and 3 LOCA Break Spectrum Analysis,"AREVA NP Inc., September 2011.2. ANP-3016(P) Revision 0, "Browns Ferry Units 1, 2, and 3 LOCA-ECCS Analysis MAPLHGRLimit for ATRIUMTM-1 0 Fuel," AREVA NP Inc., December 2011.3. NRC Letter, "Browns Ferry Nuclear Plan, Unit 1 -Issuance of Amendments Regarding theTransition to AREVA Fuel (TAC No. ME3775) (TS-473)," April 27, 2012.4. FAB1 2-2249, "Transmittal of 10 CFR 50.46 PCT Error Reporting for Browns Ferry Units 1, 2,and 3," AREVA NP Inc., June 28, 2012.5. NEDC-32484P Revision 6, "Browns Ferry Nuclear Plant Units 1, 2, and 3: SAFER/GESTR-LOCA Loss-of-Coolant Accident Analysis," GE Nuclear Energy, February 2005.6. NEDC-32484P Revision 6, Supplement 2 Revision 0, "Browns Ferry Nuclear Plant Unit 1:Supplementary Report Regarding ECCS-LOCA Evaluation Additional Single FailureEvaluation at Current Licensed Thermal Power," GE-Hitachi Nuclear Energy,September 2012.7. GE-Hitachi 10 CFR 50.46 Notification Letter 2011-02, July 20, 2011.8. GE-Hitachi 10 CFR 50.46 Notification Letter 2011-03, July 20, 2011.9. GE-Hitachi 10 CFR 50.46 Notification Letter 2012-01, November 29, 2012.Enclosure -4 of 4