ML23087A098

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Nrc'S Methodology to Estimate Fuel Dispersal During a Large Break Loss of Coolant Accident, EPRI Atf/Hbu Workshop 2023
ML23087A098
Person / Time
Issue date: 03/28/2023
From: Andrew Bielen
NRC/RES/DSA
To:
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Download: ML23087A098 (19)
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NRCs Methodology to Estimate Fuel Dispersal during a Large Break Loss of Coolant Accident Andy Bielen, James Corson, and Joe Staudenmeier Division of Systems Analysis Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission

FFRD as Applied to Plant Calculations What are the cladding temperatures as a function of How many rods time through the core? (i.e. not just the hot rod PCT) rupture?

Whats the burnup of each ruptured How much fuel disperses?

rod?

Current work: estimating the blue boxes What are the consequences of dispersal?

Transport:

Terminal Pressure Chemical velocity of Coolability Dose GSI-191 Pulse Effects buoyancy 2

force

Plant Calculations: Motivations

  • NRC is demonstrating its analysis capabilities

- Selected boundary conditions may not be representative of licensing approaches

- One should not draw conclusions on fuel safety based on this initial analysis

  • NRC staff can leverage experience gleaned developing this tool to help prepare for topical report submittals from fuel vendors

- Vendors may use similar approaches to quantify how many high burnup rods burst, how much fuel is released

- Risk-informed approaches may still require assessment of potential FFRD consequences

  • Tool could provide reasonable starting point for consequence analysis 3

Overall Approach

  • Goal: estimate mass loss from FFRD during large break loss of coolant accident (LBLOCA)
  • Approach:

- Polaris/PARCS for core depletion calculations - generate fuel operating histories

- FAST for steady-state fuel performance (FP)

- TRACE for core & system thermal-hydraulics (T/H) during transient of interest at core statepoint of interest

- FAST for transient FP - calculate burst population of HBU fuel rods

  • Burnup distribution + burst characteristics -> RIL FFRD models ->

Estimated mass loss

  • Target demonstration: end of cycle (EOC) of an high burnup (HBU)/extended enrichment (EE) core design (5 wt/o to 8 wt/o enriched fuel) 4

Workflow for Holistic Accident Multi-physics Data: Core/fuel Core depletion simulation:

design, Polaris/GenPMAXS/PARCS operating (assembly-based) conditions Pin power Pin power Fuel history simulation: reconstruction reconstruction FAST (representative rods per assembly)

Pre-transient fuel condition :

representative rods per assembly Fuel history simulation:

FAST (pin-by-pin)

Transient simulation:

TRACE (assembly-based T/H, representative fuel rods per assembly) Transient fuel performance: FAST (pin-Transient thermal/hydraulic Pre-transient fuel condition :

conditions: assembly-based by-pin resolution) pin-by pin Burnup distribution and burst strains/locations Blue: Assembly-level calculations RIL FFRD Empirical Models Orange: Pin-level calculations Fuel mass loss to RCS 5

Core and Fuel Design Description H G F E D C B A

  • Prospective EE/HBU loading for a 8 5.95 l 200 FEED 5.95 l 200 H-6 5.95 l 200 FEED 5.95 l 200 N-4 5.95 l 200 F-4 5.95 l 80 B-8 5.95 l 200 FEED 5.95 l 200 K-6 Westinghouse (W) 4-loop core 0.0 / 37.2 37.2 / 67.6 0.0 / 37.2 35.1 / 64.6 35.1 / 64.0 35.1 / 65.4 0.0 / 33.5 36.8 / 52.4 5.95 l 200 5.95 l 200 l 24 5.95 l 200 5.95 l 200 l 24 6.20 l 200 5.95 l 200 5.95 l 200 l 20 5.95 l 200 obtained from DOE NEAMS 9 F-8 FEED J-9 FEED F-2 FEED FEED N-9 37.2 / 67.6 0.0 / 34.9 34.1 / 65.4 0.0 / 34.0 32.5 / 63.5 0.0 / 37.9 0.0 / 32.0 37.9 / 52.7 program 5.95 l 200 5.95 l 200 5.95 l 200 5.95 l 200 5.95 l 200 l 24 6.20 l 200 5.95 l 104 5.95 l 200
  • 24-month cycle length 10 FEED M-10 FEED E-7 FEED B-5 FEED 0.0 / 37.2 35.1 / 66.1 0.0 / 36.8 34.2 / 64.2 0.0 / 34.6 29.6 / 62.9 0.0 / 33.5 55.6 / 67.4 P-12 5.95 l 200 5.95 l 200 l 24 5.95 l 200 5.95 l 200 5.95 l 200 5.95 l 200 6.20 l 200 l 8 6.20 l 200 Feed enrichment 5.95 wt/o to 11 D-3 FEED G-5 D-13 G-2 FEED FEED J-4 6.60 wt/o 35.1 / 64.6 0.0 / 33.9 34.3 / 64.2 35.1 / 63.3 32.0 / 62.6 0.0 / 37.6 0.0 / 29.0 61.1 / 69.9 5.95 l 200 6.20 l 200 5.95 l 200 l 24 5.95 l 200 6.60 l 128 5.95 l 200 5.95 l 200
  • End-of-life assembly burnups >71 12 D-10 P-10 FEED P-9 C-13 FEED 35.1 / 64.0 32.6 / 63.5 0.0 / 34.6 32.1 / 62.7 29.5 / 62.3 0.0 / 34.8 37.4 / 55.3 N-5 GWd/MTU 13 5.95 l 80 H-14 5.95 l 200 FEED 6.20 l 200 L-14 5.95 l 200 FEED 5.95 l 200 FEED 6.60 l 156 FEED 5.95 l 200 R-9
  • W VANTAGE+ fuel design 35.1 / 65.4 0.0 / 37.9 29.6 / 62.9 0.0 / 37.6 0.0 / 34.8 0.0 / 28.9 51.9 / 61.8 5.95 l 200 5.95 l 200 l 20 5.95 l 104 6.20 l 200 l 8 5.95 l 200 5.95 l 200
  • Early-cycle excess reactivity 14 FEED FEED FEED FEED L-3 0.0 / 33.5 0.0 / 32.0 0.0 / 33.6 0.0 / 29.1 37.4 / 55.3 52.8 / 62.7 G-1 controlled with integral fuel 15 5.95 l 200 F-6 5.95 l 200 J-13 5.95 l 200 D-2 6.60 l 156 M-4 Enr l IFBA l WABA PrevCycLoc burnable absorber (IFBA) and wet 36.8 / 52.4 37.9 / 52.8 55.6 / 67.5 62.0 / 71.0 BOC/EOC BU annular burnable absorber Quarter-core representation of core (WABA) loading pattern for presentation -
  • One possible fuel management modeling is performed in full-core strategy for HBU/EE 6

Steady State Results

  • Cycle depletion results generally in good agreement with NEAMS and utility results
  • Fuel performance show this is a very aggressive (and probably unrealistic) core design

- Very high fission gas release, rod internal pressure, cladding strain

  • Pin-by-pin results provide more clarity about fuel performance trends 7

Steady-State FP at EOC Linear Heat Generation Rate Fission Gas Release Rod Internal Pressure

  • Calculations and conclusions are produced for code readiness demonstration 8 purposes only and are not representative of actual licensee designs or analysis.

TRACE Model Description

  • Calculations use a 4-loop Westinghouse model
  • Model uses cartesian vessel component for the active core

- Each assembly represented by vessel node in XY plane

- 3 heat structures per assembly: representative IFBA, representative non-IFBA, and hot rod

cartesian core) model have been run using various input permutations

- Run with TRACE V5.0 patch 7RC3

- 350 s of simulation time took ~5.5 days wall time 9

TRACE PCT vs. Time Axial power distribution sensitivity - Resulting PCT trends - rough candidate shapes surrogate for overall core heat-up

  • Calculations and conclusions are produced for code readiness demonstration 10 purposes only and are not representative of actual licensee designs or analysis.

Transient Fuel Performance Results

  • Significant fraction of rods burst for all cases

- 64% for base case

- > 75% for Top peak cases

- All others closer to base case

  • Most bursts occurred near the top of the rod during reflood

- However, burst timing and location depends strongly on axial power profile

  • Burst temperature tended to be low compared to Chapman correlation in NUREG-0630
  • Relatively large amount of dispersed fuel based on models in the RIL

- Likely conservative due to conservative models in RIL and potentially conservative predictions of burst

  • Calculations and conclusions are produced for code readiness demonstration 11 purposes only and are not representative of actual licensee designs or analysis.

Base Case Burst Results Burst (red/magenta) vs. non-burst End of cycle linear heat rate (blue/cyan) rods (kW/m)

  • Calculations and conclusions are produced for code readiness demonstration 12 purposes only and are not representative of actual licensee designs or analysis.

Fuel Dispersal

  • Models from Appendix A of RIL 2021-13 used to estimate full-core dispersed mass

- Model C: All fuel in nodes with burnup > 55 GWd/MTU and hoop strain > 3%

- Model A: Fraction of fuel in nodes with burnup > 55 GWd/MTU and strain > 3%

  • Fraction = min(1.0, 0.04 * (BU - 55 GWd/MTU))
  • Based on mass fraction < 1 mm as function of burnup from SCIP, Halden)
  • Models assume:

- Fragments can travel long distance to get to burst opening

- Large burst opening size

  • Calculations and conclusions are produced for code readiness demonstration 13 purposes only and are not representative of actual licensee designs or analysis.

Dispersed Mass Results Base Case Chopped Cosine Power Profile

  • Calculations and conclusions are produced for code readiness demonstration 14 purposes only and are not representative of actual licensee designs or analysis.

Conclusions from Analytical Work

  • NRC has developed and demonstrated its WHAM methodology to estimate fuel dispersal

- Experience with our own methods may be useful when supporting future licensing reviews

  • This exercise has identified several areas for improvement

- Upgrades to PARCS to improve intra-bundle predictions

- Better modeling of connections between cartesian vessel (core) and cylindrical vessel (upper/lower plena) in TRACE

- Improvements to transient FGR models in FAST

- Additional code validation

  • FAST assessments against available LOCA and transient FGR tests ongoing
  • Again, this is only a demonstration 15

BACKUP SLIDES 16

Cycle Depletion Results NEAMS Results - VERA NRC Results - Polaris/PARCS Parameter Utility Simulation NEAMS NRC Maximum fuel rod power (-) 1.49 1.51 1.52 Maximum local pin power (-) 1.76 1.85 1.91 Maximum assembly power (-) 1.39 1.39 1.40 Maximum boron concentration (ppmB) 1568 1586 1573

  • Calculations and conclusions are produced for code readiness demonstration 17 purposes only and are not representative of actual licensee designs or analysis.

TRACE Model 18

Comparison to Chapman Correlation Burst results from the FAST base Figure 3 of NUREG-0630, showing case calculations the Chapman correlation vs. burst test data

  • Calculations and conclusions are produced for code readiness demonstration 19 purposes only and are not representative of actual licensee designs or analysis.
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