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Presentations for July 30, 2020 Higher Burnup Workshop - EPRI Presentation
	ML20211L077
Person / Time
Site:	Nuclear Energy Institute
Issue date:	07/28/2020
From:	Smith F; Electric Power Research Institute, Licensing Processes Branch, Nuclear Energy Institute, Westinghouse
To:	Michael Orenak; Licensing Processes Branch
	Orneak M
Shared Package
ML20211L075	List: ML20211L077; ML20211L080; ML20211L082; ML20211L086;
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	Download: ML20211L077 (13)
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Alternative Licensing Strategy Risk Informed Analysis of Loss of Coolant Accident Induced Fuel Fragmentation, Relocation, and Dispersal Fred Smith - Technical Executive FRP NRC High Burnup Workshop July 30, 2020 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.

Issue Statement Enhancements to fuel safety, reliability, efficiency and economics are critical to the industry, now and into the future Evolutionary fuel designs and materials (both cladding and pellets) have enabled increases in discharge burnup limits and uranium enrichments over the past several decades

- Burnup limit currently at 62 GWd/MTU (rod average)

- Enrichment limit currently at 5 weight percent U-235 One generic issue for increasing burnup limit has been identified by the U.S.

NRC as Fuel Fragmentation, Relocation, and Dispersal (FFRD) with fuel rod burst/rupture during design basis accidents (Ref: SECY-15-0148)

Risk-informed methodologies are an effective method of identifying and addressing safety significant issues associated with design changes.

Challenges to Fuel Fragmentation, Relocation, and Dispersal (FFRD) Project Plans Challenges to FFRD and Loss of Coolant Accident (LOCA) Testing Plans

- Irradiated fuel shipments to INL delayed - Waste Treatment Operation

- Other Schedule Uncertainties LOCA/FFRD test execution Data Analysis and Modeling Topical development and approval Are there alternative licensing strategies with lower risk?

Alternative Licensing Strategy Evaluation Project (Phase I)

- Public Document

Alternative Licensing Strategy Evaluation Project Collaboration Team Members

- Utilities

- Fuel Vendors

- EPRI

LOCA Reactor Coolant System (RCS) Pipe Rupture Frequency and Impact on FFRD Large Break LOCA (LB-LOCA) Events

- Low Probability Event Cladding Burst likely for high burnup interior fuel Not Likely for peripheral fuel Small Break LOCA (SB-LOCA) Events

- Higher Probability Events

- Cladding Burst Lower peak cladding temperatures Burst not likely for high burnup pins Intermediate - Similar to small break

NUREG-1829, Vol. 2, Table 1 events 5 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.

Leak Before Break (LBB)

EPRI/NRC are finalizing xLPR (extremely low probability of rupture) models which supports risk evaluations of pipe rupture events Probabilistic Fracture Mechanics - Predicts probability of pipe rupture for defined leakage rate

- Well characterized treatment of uncertainties

- Active degradation mechanisms

- Seismic Considerations

- Inspection and mitigation activities All PWR Technical Specifications have 1 GPM unidentified leakage Limited Condition of Operations (LCO)

- Mode 3 (Hot Standby) in 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months

- Mode 5 (Cold Shutdown) in 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months

- 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months after shutdown decay heat ~0.6 % of full power - LOCA non-event

- xLPR Applications Time to detect flaws leading to pipe rupture depends on pipe size

- Large breaks detected well in advance

- Small breaks more difficult to detect in short time frame Estimate that timely detections are limited to ~10 Validate NUREG-1829 conclusions 6 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.

Risk Informed Analysis of LOCA induced FFRD

Based on existing process - RG-1.174

Small increase in Core Damage Frequency (<10-6) and Large Early Release Fraction (<10-7)

Large Break - Credit Plant Shutdown (Leak Before Break) prior to LOCA

Small Break - No cladding rupture for high burnup fuel

Ensure overlap addresses Intermediate Break

Feasibility evaluations show lower risk than the target criteria by factor of 10 (regulatory margin)

Defense in Depth/Safety Margins

Seven Principles for Defense in Depth addressed

Maintained with combination of SB-LOCA analysis results and Leak Before Break mitigation for LB-LOCA

Risk Informed Process Based on RG 1.174 Process Licensing basis changes must:

1. Meet current regulations unless related to exemption request

2. Be consistent with defense in depth

3. Maintain sufficient safety margins

4. Result in no more than a small increase in risk

Other Expectations within RG 1.174 Process Benefits commensurate with risk increases Analyses based on as-built and operated plant Plant specific PRA acceptable Appropriate consideration of uncertainty Increases in CDF and LERF limited to small increments Evaluated in integrated fashion Data, methods, and assessment criteria well documented 9 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.

Phase II - Identified Gaps for Phase II Validate LOCA rupture frequencies for 80-year operating life (xLPR)

Determine fleet conditional containment failure probability Establish bases for FFRD probability inputs to PRA analysis Generic Small/Intermediate break size LOCA (no clad rupture)

Demonstrate leak before break for Large and Intermediate break sizes Impacts of fuel fragmentation relocation into balloon region w/o rupture Demonstrate acceptable impact on Safety Margins Fuel dispersal model as backup to Defense-in-Depth arguments 10 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.

Phase II - Gap Closure and Implementation (contd)

Questions?

ML20211L077

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