ML17306A084

11/06/2017, Meeting Slide for Teleconference with Exelon Generation Company, LLC - Criticality Analysis for NMP1 Boraflex Racks: No Boraflex Credit, 3 Out of 4 Loading, and Cell Blockers

ML17306A084
Person / Time
Site:	Nine Mile Point
Issue date:	11/06/2017
From:	Exelon Generation Co
To:	Marshall M Plant Licensing Branch 1
Marshall M
Shared Package
ML17306A083	List: ML17306A084
References
Download: ML17306A084 (13)

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Criticality Analysis for NMP1 BoraflexRacks: No BoraflexCredit, 3 out of 4 Loading, and Cell BlockersNovember 6, 2017Pre-Submittal Briefing Introduction NMP1 Spent Fuel Pool (SFP) 2 BoraflexRacks + 14 Boral RacksConcerns of Boraflexdegradation: proactively and conservatively address What to Do?Perform a new criticality analysis for the 2 BoraflexracksoNo credit is taken for the residual Boraflex3 out of 4 loading pattern is used to reduce reactivity oPermanent Cell Blockers will be installed in accordance with NEI 12-16No changes were made on the Boral racksRevision to Technical Specifications (TS) 5.5 will be made on non-poison flux trap racks and Boraflexracks to reflect the current pool configuration and description in the current UFSAR.NMP1 Criticality Analysis1 New Criticality Analysis OverviewConsistent with the Peak Reactivity Methodology Previously Approved Quad Cities: ML14346A306/ML16231A131Dresden: ML15343A126In Compliance with Current Industry Guidance/Standards10 CFR 50 Section 68 and Appendix AKopp MemorandumDSS-ISG-2010-01NEI 12-16Computer Codes: CASMO & MCNP5-1.51NMP1 Criticality Analysis2 Analysis Results Summary Permanent cell blockers will be installed in specific locations in BoraflexracksoMaintains a sufficiently low reactivity area along interface with Boral racksoPrecludes the need to leave an entire empty row along the interface with Boral racksMisload accident is precluded oPeak reactivity lattice is usedoThe empty cells are blocked with cell blockersFinal K-effo0.9390: all normal/accident conditions and uncertainties and biasesoMargin to regulatory limit of 0.011ooSupports application of current TS limits for Boral Racks to BoraflexracksAchieves commonality and consistency between Boral and BoraflexracksNMP1 Criticality Analysis3 Criticality Safety Analysis SpecificsBoraflexStorage Rack DesignNMP1 Criticality Analysis4 SW Corner Storage Rack Configuration in SFPNMP1 Criticality Analysis5 No poison so maximum temperature is used (100 C, also bounds accident condition)Cell blockers are not modeled explicitly; steel is an absorber.Eccentric positioning and channel inclusion treated as a bias (bounding case is no channel, all eccentric to rack center; bias = 0.0182)Peak reactivity isotopic compositions from CASMO depletion calculations considering bounding Core Operating Parameters (COP)All reactivity calculations for K-eff determination are performed using MCNP5-1.51Accident conditions evaluated:Dropped bundle outside the racks, rack movement, pool temperature.NMP1 Criticality Analysis6 Criticality Safety Analysis Specific ResultsAll actual as-built NMP1 fuel bundle lattices evaluated.Most reactive as-built actual lattice studies show that the negative reactivity introduced by the cell blockers > 0.11 delta-kMaximum K-calcfor as-built lattices in the Boraflexracks with cell blockers is ~ 0.82NMP1 Criticality Analysis7 Interface EvaluationBoraflexRacksLocated in the SW corner and adjacent to 14 Boral racks along the east and north-SThe geometry of the Boraflexracks with cell blockers creates a low reactivity configuration (Max K-calc=0.82 for as-built lattices).Boral RacksBoral neutron absorber panels on the outside of the Boral racks along the interface significantly reduce reactivity in the interface area.Interface gapsare larger than the Flux traps in Boraflexracks and hence further reduce the reactivity in the interface area.NMP1 Criticality Analysis8 Cell to Cell PitchBoth racks are nearly identical for the N-S cell pitches.E-BoraflexTherefore, the racks on one side of the interface can be assumed to be a continuation of the rack on the other side of the interface.Max SFP temperature used, which yields 0.0144 delta-k over Min SFP temperatureThe bounding reactivity of the Boraflexrack used to show compliance with the regulatory requirements is K-calc= 0.8697Interface Evaluation Conclusion:The interface between the Boraflexand Boral racks in the SFP is an area of low importance (i.e., low reactivity) and no further evaluations are required. NMP1 Criticality Analysis9 TS EvaluationThe Boral rack TS requires that all fuel lattices have a maximum enrichment of 4.6% U-Will apply Boral racks TS to Boraflexracks.Super lattices were created from the existing most reactive as-built lattices to bound the above TS requirements.Enrichment of each pin was increased to 4.6% U-235 and Gdrod loading was varied until the super lattice SCCG was slightly above 1.31Each super lattice has a unique Gdloading that yields a SCCG of at least 1.31Design Basis Lattice The most reactive lattice (peak reactivity in the Boraflexrack) of all super lattices Used to perform the analysis calculations to show compliance with regulatory requirements (i.e., determination of Total Correction Factor (TCF))NMP1 Criticality Analysis10 Final Analysis ResultsBias & Unc0.0693Normal Keff0.9370Accident Keff0.9390Gray BoxesproprietaryNMP1 Criticality Analysis11 ConclusionsMeet 10 CFR 50.68 (b)(4) requirement:The effective neutron multiplication factor (Keff) is less than or equal to 0.95 for all normal and accident conditions with 95% probability at a 95% confidence level.Supports application of current TS limits for Boral Racks to Boraflexracks wt% U-235 Lattice standard cold core geometry (SCCG) KinfQuestions and CommentsThanksNMP1 Criticality Analysis12