ML15105A037

Xcel Energy Slide Presentation to Support Pre-Application Meeting on April 14, 2015, to Discuss Nuclear Fuel Design Transition to Include Integral Fuel Burnable Absorber (Ifba) at the Prairie Island Nuclear Generating Plant

ML15105A037
Person / Time
Site:	Prairie Island
Issue date:	04/14/2015
From:	Xcel Energy
To:
Beltz T
Shared Package
ML15107A060	List: ML15105A037 ML15107A059
References
TAC MF5839, TAC MF5840
Download: ML15105A037 (42)

Text

Prairie Island Nuclear Generating Plant (PINGP)

Pre-Application Meeting April 14, 2015 Nuclear Fuel Design Transition to Include Integral Fuel Burnable Absorber (IFBA) 1

Agenda

• Purpose / Objectives / Principles

• Current Condition

• Merits of IFBA-Gad

• Scope of Licensing

• Spent Fuel Pool (SFP) Criticality Analysis

• Schedule

• Conclusion / Summary 2

Meeting Purpose

• Describe an Xcel Energy initiative to use IFBA and Gadolinium (Gad) neutron absorbers in the Westinghouse 422 Vantage Plus (422V+) fuel assembly design for PINGP operations and fuel storage

• Describe preliminary evaluation of the effects of this proposed change and the extent of NRC review that may be required 3

Meeting Objectives

• Common understanding of licensing scope

• Common understanding of schedule

• NRC feedback

• NRC expectations for submittal content

• Actions 4

Principles

• Maintain nuclear safety margins

• Reliable power in the Midwest Region

• High confidence in refueling cycle timing

• Reduce spent fuel inventory

• Maintain regulatory margin

• No impact on plant operations

• No new impact on storage (human factors) 5

Current Condition PINGP Description

• 2-reactor site

• 2-loop Westinghouse NSSS

• Vantage 422+ with Optimized ZIRLOTM Fuel

• Previously-used grid and nozzle designs

• Gadolinium burnable poison

• Currently operating 18-23 month cycles Optimized ZIRLO is a trademark of Westinghouse Electric Company LLC, its Affiliates and/or its Subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved.

Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.

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Current Condition PINGP Spent Fuel Pool (SFP) Description

• Criticality Safety Analysis approved in 2013

• Compliant to DSS-ISG-2010-01

• No credit for SFP neutron absorber (Boraflex)

• Subcriticality criteria met by reactivity balancing (checkerboarding) 7

Current Condition Independent Spent Fuel Storage Installation

• Site-specific license for TN-40 cask storage

• IFBA-Gad not specifically licensed

• 10-year decay time requirement for spent fuel 8

Design Optimization Xcel Energy and Westinghouse investigated optimizing the Prairie Island fuel management while maintaining the current reload plan

• Maintain or improve safety margins

• Minimize assemblies requiring storage

• Maximize fuel cycle economics 9

Design Optimization Gad alone has negative impact on economics

• Displaces uranium, decreasing core loading

• Residual reactivity hold down at end-of-cycle

• Requires additional assemblies to be loaded each cycle or increased fuel enrichment

• Reduced gad loading results in unacceptably high soluble boron concentrations 10

Design Optimization IFBA

Description:

Advanced fuel development program in the early 1980s led to development of a thin ZrB2 coating on the UO2 pellet as the optimum design

• Integral to fuel rod, no separate component handling

• Complete depletion, no residual penalty

• No residual poison, no displaced uranium

• Dilute absorber, low power peaking

• ZrB2 extensively used in Westinghouse PWRs today 11

Design Optimization IFBA alone has limited reactivity control

• Provides diminishing reactivity hold down over cycle

• IFBA depletion rate higher at Beginning of Cycle (BOC)

• Results in soluble boron increases at BOC

• Loading IFBA alone results in unacceptably high soluble boron concentrations 12

Merits of IFBA-Gad IFBA-Gad combination optimizes all three parameters

• IFBA and Gad not in the same fuel pin

• Combination maximizes or maintains safety margins

• IFBA provides the necessary cycle length benefit to reduce assembly loading and maximize fuel economics

• Gad provides the necessary reactivity hold down to obtain acceptable soluble boron concentrations

• Both IFBA and Gad have extensive operating experience 13

Merits of IFBA-Gad 14

Fuel Storage Considerations ISFSI will not require amendment until 2032

• 2018 First IFBA-Gad fuel load

• 2022 First discharge of IFBA-Gad (2 cycles)

• 2032 First IFBA-Gad in storage (10 yr decay)

Spent Fuel Storage Requirements

• 39 fewer spent fuel assemblies over plant life

• 1 fewer spent fuel cask 15

Scope of Licensing Preliminary TS / 50.59 Reviews of IFBA-Gad

• Reactor operations

• SFP operations Preliminary

Conclusion:

License Amendment for

• SFP Criticality Technical Specification (TS) changes 16

Scope of Licensing TS Review - Reactor No TS changes for fuel design change

• TS 2.1.1.2.b Gad thermal conductivity penalty is unchanged

• TS 4.2.1 description does not constrain IFBA 17

Scope of Licensing 50.59 Review - Reactor No new material interactions, no new type of failure

• Fabrication processes are unchanged

• Use existing Gad and IFBA specifications, good OE No increased probability of failure (e.g., clad failure)

• Clad, geometry, weight, strength is same No increased consequence of failure

• Radiological source term change is insignificant 18

Scope of Licensing Conclusion - Reactor

• No TS changes required

• No 50.59 criteria exceeded

• Prior NRC approval not required for reactor operations 19

Scope of Licensing TS Review - SFP

• TS do not constrain fuel design in SFP

• Coefficients in TS Table 4.3.1 will change slightly Bu = A1*En3 + A2*En2 + A3*En + A4 20

Scope of Licensing 50.59 Review - SFP No increased probability of failure (e.g., drop, clad failure)

• Clad, geometry, weight, strength, decay heat are same No increased consequence of failure

• Radiological source term change is insignificant Methods of Evaluation

• Same calculational framework (WCAP-17400-P) 21

Scope of Licensing Conclusion - SFP

• No 50.59 criteria exceeded

• TS (Table 4.3.1) changes required

• Prior NRC approval required for criticality function 22

Background - LAR Scope No Complicating Factors:

• No significant change in fuel design

• No credit for neutron poison inserts

• No rerack, no rack design changes

• No new SFP loading restrictions

• No New Fuel Vault analysis 23

Licensing Schedule 11/2015 Submit SFP Criticality LAR 11/2017 License Amendment 8/2018 Receipt of IFBA-Gad Fuel 24

Spent Fuel Criticality Analysis Outline

• Supplement Scope

• Comparison with Current Analysis of Record

• Compliance to DSS-ISG-2010-01 (ISG)

• Summary

• Conclusions 25

Spent Fuel Criticality Analysis Supplement Scope

• Supplement WCAP-17400 (AoR) w/ IFBA-Gad

• Incorporate multiple misload accident

• Retain compliance with ISG

• Determine TS impacts 26

Spent Fuel Criticality Analysis Analysis-of-Record (AoR) WCAP-17400

• Approved in 2013

• Compliant to ISG

• 422V+ is limiting fuel design

• IFBA-Gad fuel not specifically addressed 27

Spent Fuel Criticality Analysis Analysis-of-Record (AoR) WCAP-17400

• Important technical conclusions

- Ignores gadolinia; shown to be conservative

- Up to 100 MWd/MTU rodded operations in SER

- Fission product worth addressed in RAIs

- Annular axial blankets conservatively modeled as solid

- Confirmation of design basis fuel type (422V+)

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Spent Fuel Criticality Analysis

• Objectives of the SFPC Analysis Supplement

- Evaluate the impact of a new burnable absorber (BA) design on the discharge reactivity

- Minimize impact on AoR (supplement format)

• Methods to be used in the analysis

- Based on current AoR calculational framework

• Selection of depletion calculation inputs

• Development of biases & uncertainties

• Accidents, interface conditions & soluble boron credit analysis 29

Spent Fuel Criticality Analysis Analysis Supplement Scope

• Configurations: no changes

• IFBA-Gad 422V+ Fuel

- No credit for gadolinia

- Planned max 120 IFBA pattern

- Cycle Avg Boron: 900 ppm to 1000 ppm

- Fuel Density: 98% TD

- Axial burnup and moderator temperature profiles

- Blankets fully enriched 30

Spent Fuel Criticality Analysis

• AoR depletion calculations based on burnup bins of 0-18, 18-30, 30-38, 38-48, and > 48 GWD/MTU

- Limiting burnup profiles from the AoR to be checked against IFBA-Gad design profiles

- Uniform profile considered

• The following slides outline potential impacts related to ISG 31

Spent Fuel Criticality Analysis ISG Criteria

• 2a - 5% decrement method for depletion uncertainty - same as AoR methodology

• 2b - Nominal values may not be appropriate, discuss selected values

- PINGP IFBA-Gad supplement analysis

• Updated conservative average cycle soluble boron concentration

• Increase in fuel theoretical density 32

Spent Fuel Criticality Analysis ISG Criteria

• 2c - Consider Burnable Absorber Usage

- IFBA-Gad rods conservatively modeled during depletion, no pool credit for residual absorber

• 2d - Consider Rodded Depletion

- No change expected due to IFBA-Gad fuel 33

Spent Fuel Criticality Analysis ISG Criteria

• 3a - Select limiting axial burnup profile using NUREG-6801 or plant-specific data

- Use bounding profile from AoR site-specific burnup profiles and IFBA-Gad design profiles

- An axially-uniform profile will be considered and used at those burnups if/when it is limiting

- Determine appropriate limiting moderator temperature profiles (distributed and uniform profile) 34

Spent Fuel Criticality Analysis ISG Criteria

• 3b - Modeling SFP racks including geometry and neutron absorbers - same as AoR Methodology

• 3c - Interfaces - no methodology impact

• 3d - Normal Conditions - no impact expected

• 3e - Accident Conditions

- Incorporation of multiple misload event

- No other changes from AoR methodology 35

Spent Fuel Criticality Analysis ISG Criteria (Section 4)

• Validation of Codes

- Code validation suite addresses ISG

- No impact to the AoR 36

Spent Fuel Criticality Analysis WCAP Supplement Format

• IFBA-Gad evaluation as WCAP-17400 Supplement

- Generate of burnup limits for IFBA-Gad with current configurations

- Evaluate normal conditions

- Evaluate interface conditions

- Update accident analysis - Including multiple misload analysis

- Soluble boron credit (normal and accident conditions) 37

Spent Fuel Criticality Analysis Spent Fuel Criticality Analysis Summary

• Addition of IFBA (IFBA/IFBA-Gad design) to AoR

• Analysis remains in alignment with ISG

• Supplement to WCAP-17400 will evaluate impact of IFBA-Gad fuel (introduction of IFBA)

- Updated burnup limits

- Updated soluble boron requirements for normal and accident conditions 38

Spent Fuel Criticality Analysis In Conclusion

• SFP criticality analysis supplement will:

- Conservatively bound proposed future operating conditions with regards to IFBA & IFBA-Gad fuel

- Address NRC Staff expectations (ISG) 39

Summary of Actions

• Xcel Energy Actions

- Points of Emphasis for LAR content

• NRC Actions 40

Summary Summary

1. Submit LAR 11/2015

2. Include NRC expectations

3. Other actions 41

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