Increased Burnup – Criticality – 09/15/21

Morris Byram, John Klingenfus & Glen Seeburger

September 15, 2021

Increased Burnup – focus on Coolability and Criticality (Closed)

Core Cooling Following FFRDJohn Klingenfus

09/15/2021

Core Cooling Following FFRD – 09/15/21

Core Coolability OutlineIntroduction & Background

Core Cooling Roadmap

Core Cooling Next Steps

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Core Cooling Following FFRD – 09/15/21

Introduction and Background

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Core Cooling Following FFRD – 09/15/21

AFM Increased Burnup with FFRD Overview (1/2)

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The AFM project goals introduce new challenges for FFRD analysis

Core Cooling Following FFRD – 09/15/21

AFM Increased Burnup with FFRD Overview (2/2)

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Framatome plans to demonstrate that if high burnup fuel rod ruptures occur with fuel dispersal, there is no impact to safety

• Criticality: demonstrate acceptable results for FFRD in reactor vessel• Dose: demonstrate that all regulatory limits continue to be met

This discussion will focus on Core Cooling following a LBLOCA

Core Cooling Following FFRD – 09/15/21

FFRD Roadmap

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LBLOCA Core Cooling Evaluation The first step to address LBLOCA core cooling with FFRD is to define the

geometrical and thermal hydraulic problem that must be evaluated.

Core Cooling Following FFRD – 09/15/21

Core Cooling Configuration Considered

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Core Cooling Following FFRD – 09/15/21

Core Cooling Configuration Considered Early Reflood

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Core Cooling Following FFRD – 09/15/21

Core Cooling Configuration Considered Mid Reflood

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Core Cooling Following FFRD – 09/15/21

Core Cooling with FFRD is Only a Concern if High Burnup Rods Rupture

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Core Cooling Following FFRD – 09/15/21

Time of Rupture from REBEKA Test Results

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Core Cooling Following FFRD – 09/15/21

Location of Rupture from REBEKA Test Results

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Core Cooling Following FFRD – 09/15/21

Variation of REBEKA Cladding Strains with Elevation

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Orientation of Burst and Location where Dispersed Particles May Accumulate

Core Cooling Following FFRD – 09/15/21

Core Cooling Roadmap

The following steps should be followed for increased burnup licensing to show that the core geometry remains amenable to cooling.

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Core Cooling Following FFRD – 09/15/21

Steps to Show Core Cooling

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Each of these steps is expanded upon in the following slides.

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Core Cooling Following FFRD – 09/15/21

Step 2 – Studsvik Test Fuel Particle Size Distributions

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The size distribution of the fuel particles that are dispersed is based on StudsvikTests 191, 192, and 193.

The burnup for Tests 191-193 were from rods with rod average burnups between 68 and 69 GWd/mtU.

The burnup for Studsvik Tests 196 and 198 were from rods with rod average burnups 55 GWd/mtU. The particle sizes are larger at this burnup, and many particles do not escape the burst opening. The larger dispersed particles will not produce debris beds with the same potential blockage and challenge to core cooling as higher burnup rods.

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Core Cooling Following FFRD – 09/15/21

Core Cooling Next Steps

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Core Cooling Following FFRD – 09/15/21

Potential Fuel Debris Grid Blockage Testing

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Core Cooling Following FFRD – 09/15/21

Core Cooling Configuration Considered for Testing

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Core Cooling Following FFRD – 09/15/21

Questions?

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Increased Burnup – Criticality – 09/15/21

Criticality Following FFRD

Glen Seeburger

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The purpose of the criticality analysis is to determine if the FFRD material can become critical after it migrates from the fuel lattice and accumulates elsewhere in the reactor vessel.

FFRD Criticality Introduction

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Increased Burnup – Criticality – 09/15/21

AssumptionsMethodologySensitivity Studies

Conclusion

Criticality Outline

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• Results presented for fuel enriched to bounding of Framatome maximum

• 2D planar average burnup: • Lower burnup is bounding for criticality• Dispersal-susceptible fragmentation is assumed

• Fuel is assumed to be without gadolinium.• Regulatory Guide 1.240, March 2021• NEI 12-16 Revision 4, September 2019

Conservative Calculation Assumptions

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• of fuel particles released based on conservative assumptions:

Conservative Calculation Assumptions – Amount of Material Released

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• Dispersed particle size distribution taken from tests 191, 192, and 193 as reported in NUREG-2160.

Conservative Calculation Assumptions – Material Migration

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Increased Burnup – Criticality – 09/15/21

• All the fuel that escapes the fuel lattice is assumed to be

Conservative Calculation Assumptions – Criticality Evaluation (1/2)

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• Fuel and moderator are combined as• Homogenized.• Uniform array of uniform size spheres arranged as a Body

Centered Cubic (BCC) lattice, with spheres 1 mm radius• Lattices of spheres of radius 2, 3, 4, and 5 mm are also analyzed

for trending.• The model allows spheres to

overlap for values greater than ~0.68. • Lopez, Buck, and Starflinger (Annals of Nuclear Energy 130,

2019) showed that a regular lattice of uniform sized sphere can adequately model a “real” debris bed that consists of randomly place particles of random size.

Conservative Calculation Assumptions – Criticality Evaluation (2/2)

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Increased Burnup – Criticality – 09/15/21

FFRD Particle Size DistributionTest Number 191 192 193 196 198Burnup (GWD/MTU) 69.3 68.2 69.3 55.2 55.2Size (mm) Mass (g)< 0.125 9.2 22.6 18.6 0.4 0.50.125 - 0.25 6.3 8 10.7 0.4 0.5.25 - 0.5 8.2 9.1 13.7 0.3 0.50.5 - 1.0 10.9 10.2 17.4 0.3 0.41.0 - 2.0 9.9 13.3 19.6 0.6 0.82.0 - 4.0 6.3 8.2 20.2 9.4 17.5> 4.0 0 0 2.1 65.9 42.1Size (mm) Mass Fraction (%)< 0.125 18 32 18 1 10.125 - 0.25 12 11 10 1 1.25 - 0.5 16 13 13 0 10.5 - 1.0 21 14 17 0 11.0 - 2.0 19 19 19 1 12.0 - 4.0 12 11 20 12 28> 4.0 0 0 2 85 68

Source: NUREG-2160, Tables 2-4, 2-6, 2-10, 2-12, and 2-16

~ 90% of dispersed fuel

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Increased Burnup – Criticality – 09/15/21

• Fuel isotopic concentrations for depleted fuel calculated by TRITON from the SCALE 6.2.1 package.

• Neutron multiplication factors calculated by MCNP5 1.6, which is widely accepted for criticality applications (LA-UR-03-9032).

Methodology

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Increased Burnup – Criticality – 09/15/21

• Dispersed fuel in the lower head modeled as a partial sphere intersecting with the center of the lower head.

• Results are presented with the following Aspect Ratios:

Aspect Ratio

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Aspect Ratio

Increased Burnup – Criticality – 09/15/21

Aspect Ratio = 0.1

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Aspect Ratio = 0.5

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Aspect Ratio = 1.0

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Sensitivity Studies

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

k-in

finity

Packing Factor

R=0 R=0.1 R=0.2 R=0.3 R=0.4 R=0.5

56 GWD/MTU, 0 ppm0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

k-in

finity

Packing Factor

R=0 R=0.1 R=0.2 R=0.3 R=0.4 R=0.5

56 GWD/MTU, 1500 ppm

Boron concentration can affect the limiting packing factor.45

Increased Burnup – Criticality – 09/15/21

Upper Plenum

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Example Upper Plenum Critical Mass Search

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• Search for critical mass for a range of conditions• Packing factor: • Moderator void fraction: • Particle size: • Particle size: • Enrichment: • Boron concentration: • Aspect ratio:

• Reflector layer for spherical geometry is , adequate for full moderator density

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• FFRD in lower head is subcritical for packing factors ≥ 0.5

Conclusions

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Overall Conclusions

EPRI: High Burnup Workshop April 2021

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• Fuel lattice: No impact.

Overall Conclusions

EPRI: High Burnup Workshop April 2021

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Increased Burnup – Criticality – 09/15/21

Questions?

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Summary & Next Steps

Morris Byram

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Increased Burnup – Criticality – 09/15/21

Summary

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High Burnup Topical Report goal is to demonstrate if high burnup fuel rod ruptures there is no safety impact FFRD Roadmap – Core Coolability and Criticality after FFRD Core coolability after FFRD

• LBLOCA core cooling overview• Core configuration and LBLOCA Scenario• Core cooling concern only if high burnup fuel rods rupture• Timing and location of rupture concerns• Fuel particle location

• Steps to show acceptable core coolability

Increased Burnup – Criticality – 09/15/21

Summary - (Continued)

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Criticality after FFRD• Conservative calculation assumptions• Criticality Methodology

• TRITON from SCALE 6.2.1 – Fuel isotopics• MCNP5 1.6 – neutron multiplication factors• Pile configuration

• Example Calculations – Upper Plenum and Lower Head• UP – Criticality not an issue• LH – if packing > 0.5, criticality no issue

Increased Burnup – Criticality – 09/15/21

Next Steps – Increased Burnup

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Additional meetings on FFRD issues

Topical report submittal

NRC approval

Increased Burnup – Criticality – 09/15/21

AcronymsAFM – Advanced Fuel Management

ANS – American Nuclear Society

ANSI – American National Standards Institute

AREA – ARCADIA Rod Ejection Accident

CE – Combustion Engineering

CHF – Critical Heat Flux

DG – Draft Guidance

ECCS – Emergency Core Cooling System

FFRD – Fuel Fragmentation, Relocation, and Dispersal

FPC – Fuel Performance Code

HPU – Hydrogen Pickup

ICSBEP – International Criticality Safety Benchmark Evaluation Project

LBLOCA – Large Break Loss of Coolant Accident

LB - Large Break

LCT – LEU-COMP-THERM

LOCA – Loss of Coolant Accident

NRC – U.S. Nuclear Regulatory Commission

PIE – Post Irradiation Examination

PNNL – Pacific Northwest National Laboratory

PWR – Pressurized Water Reactor

RAI – Request for Additional Information

RCS – Reactor Coolant system

RIA – Reactivity Insertion Accident

RLBLOCA – Realistic Large Break Loss of Coolant Accident

SB – Small Break

SBLOCA – Small Break Loss of Coolant Accident

SRP – Standard Review Plan

W - Westinghouse

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Increased Burnup – Criticality – 09/15/21

ARCADIA, AREA, ARITA, COPERNIC, GAIA, GALILEO, M5Framatome, PROtect, and S-RELAP5 are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries.

Trademarks

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Acknowledgment: “This material is based upon work supported by the Department of Energy under Award Number DE-NE0008818.”

DOE Acknowledgment and Disclaimer

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Disclaimer: “This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.”

Increased Burnup – Criticality – 09/15/21

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Thank You!