ML17306A084

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)

Text

Criticality Analysis for NMP1 Boraflex Racks: No Boraflex Credit, 3 out of 4 Loading, and Cell Blockers November 6, 2017 Pre-Submittal Briefing

Introduction

• NMP1 Spent Fuel Pool (SFP) 2 Boraflex Racks + 14 Boral Racks

• Whats the Problem?

Concerns of Boraflex degradation: proactively and conservatively address

• What to Do?

Perform a new criticality analysis for the 2 Boraflex racks o No credit is taken for the residual Boraflex 3 out of 4 loading pattern is used to reduce reactivity o Permanent Cell Blockers will be installed in accordance with NEI 12-16 No changes were made on the Boral racks Revision to Technical Specifications (TS) 5.5 will be made on non-poison flux trap racks and Boraflex racks to reflect the current pool configuration and description in the current UFSAR.

1 NMP1 Criticality Analysis

New Criticality Analysis Overview

• Consistent with the Peak Reactivity Methodology Previously Approved Quad Cities: ML14346A306/ML16231A131 Dresden: ML15343A126

• In Compliance with Current Industry Guidance/Standards 10 CFR 50 Section 68 and Appendix A Kopp Memorandum DSS-ISG-2010-01 NEI 12-16

• Computer Codes: CASMO & MCNP5-1.51 2 NMP1 Criticality Analysis

New Criticality Analysis Overview (Contd)

• Analysis Results Summary Permanent cell blockers will be installed in specific locations in Boraflex racks o Maintains a sufficiently low reactivity area along interface with Boral racks o Precludes the need to leave an entire empty row along the interface with Boral racks Misload accident is precluded o Peak reactivity lattice is used o The empty cells are blocked with cell blockers Final K-eff o 0.9390: all normal/accident conditions and uncertainties and biases o Margin to regulatory limit of 0.011 o Includes an additional Administrative margin of 0.01 (biases) in SCCG value o Supports application of current TS limits for Boral Racks to Boraflex racks Achieves commonality and consistency between Boral and Boraflex racks 3 NMP1 Criticality Analysis

Criticality Safety Analysis Specifics

• Boraflex Storage Rack Design 4 NMP1 Criticality Analysis

Criticality Safety Analysis Specifics (Contd)

• SW Corner Storage Rack Configuration in SFP 5 NMP1 Criticality Analysis

Criticality Safety Analysis Specifics (Contd)

• 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 MCNP5-1.51

• Accident conditions evaluated: Dropped bundle outside the racks, rack movement, pool temperature.

6 NMP1 Criticality Analysis

Criticality Safety Analysis Specific Results

• All 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-k

• Maximum K-calc for as-built lattices in the Boraflex racks with cell blockers is ~ 0.82 7 NMP1 Criticality Analysis

Interface Evaluation

• Boraflex Racks Located in the SW corner and adjacent to 14 Boral racks along the east and north Old flux trap style design: Flux traps (1.72) are parallel to N-S The geometry of the Boraflex racks with cell blockers creates a low reactivity configuration (Max K-calc=0.82 for as-built lattices).

• Boral Racks Boral neutron absorber panels on the outside of the Boral racks along the interface significantly reduce reactivity in the interface area.

• Interface gaps East interface gap is 3.15 and north interface gap is 1.9. Both gaps are larger than the Flux traps in Boraflex racks and hence further reduce the reactivity in the interface area.

8 NMP1 Criticality Analysis

Interface Evaluation (Contd)

• Cell to Cell Pitch Both racks are nearly identical for the N-S cell pitches.

E-W cell pitches are 7.805 for Boraflex and 6.06 for Boral racks.

Therefore, 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 temperature

• The bounding reactivity of the Boraflex rack used to show compliance with the regulatory requirements is K-calc = 0.8697

• Interface Evaluation

Conclusion:

The interface between the Boraflex and Boral racks in the SFP is an area of low importance (i.e., low reactivity) and no further evaluations are required.

9 NMP1 Criticality Analysis

TS Evaluation

• The Boral rack TS requires that all fuel lattices have a maximum enrichment of 4.6% U-235 and a SCCG 1.31.

• Will apply Boral racks TS to Boraflex racks.

• 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 Gd rod loading was varied until the super lattice SCCG was slightly above 1.31 Each super lattice has a unique Gd loading that yields a SCCG of at least 1.31

• Design Basis Lattice The most reactive lattice (peak reactivity in the Boraflex rack) of all super lattices Used to perform the analysis calculations to show compliance with regulatory requirements (i.e., determination of Total Correction Factor (TCF))

10 NMP1 Criticality Analysis

Final Analysis Results

• Bias & Unc 0.0693

• Normal Keff 0.9370

• Accident Keff 0.9390

• Gray Boxes proprietary 11 NMP1 Criticality Analysis

Conclusions

• Meet 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 Boraflex racks Lattice initial maximum planar average enrichment (MPAE) 4.6 wt% U-235 Lattice standard cold core geometry (SCCG) Kinf 1.31

• Questions and Comments Thanks 12 NMP1 Criticality Analysis