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U.S.NRC 2014 FRAPCON/FRAPTRAN Code Applications and Developments

U.S.NRC 2014 FRAPCON/FRAPTRAN Code Applications and Developments. Patrick Raynaud, Ph.D. United States Nuclear Regulatory Commission (U.S.NRC) Washington, DC, 20555, USA Tel: +1-301-251-7542 Email: Patrick.Raynaud@nrc.gov FRAPCON/FRAPTRAN User Group Meeting September 18, 2014.

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U.S.NRC 2014 FRAPCON/FRAPTRAN Code Applications and Developments

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  1. U.S.NRC 2014 FRAPCON/FRAPTRAN Code Applications and Developments Patrick Raynaud, Ph.D. United States Nuclear Regulatory Commission (U.S.NRC) Washington, DC, 20555, USA Tel: +1-301-251-7542 Email: Patrick.Raynaud@nrc.gov FRAPCON/FRAPTRAN User Group MeetingSeptember 18, 2014

  2. U.S. NRC Research2014 Applications and Developments • FRAPCON • IFA-716 fission gas release modeling • Grain size and fission gas release models • FRAPCON-DATING/SFMOD • Extended spent fuel storage modeling • Incorporation of DATING • Spent Fuel MODification: additional gas moles and fuel swelling • FRAPTRAN • WGFS RIA benchmark phase 2 • Convergence difficulties • FEA model • FRAPCON/FRAPTRAN • Fuel dispersal calculations • Code modernization • Gamma heating • FRAPCON coolant temperatures and pressures • FRAPCON deformation printouts and gap printout bug • FRAPTRAN/TRACE coupling FRAPCON/FRAPTRAN User Group Meeting

  3. Presented at EHPG September 11, 2014 IFA-716Background and Objectives • The IFA-716 test provided experimental data to evaluate fission gas release (FGR) models in fuel performance codes • Test rods were instrumented with pressure gauges and linear variable differential transformers • Fission gas release behavior can determined from known pressures and rod free volume • 4 rods: • Rod 1: UO2 with 0.16% Cr2O3 pellets, 71 μm grains • Rod 2: UO2 pellets, 11 μm grains (Halden data was poor quality, likely transducer failure) • Rod 5: UO2 pellets, 55 μm grains • Rod 6: UO2 with 0.1% Cr2O3 pellets, 59 μm grains • Objectives: • Calculate the rod free volume, gas temperature, and fission gas production • Combine the above information from FRAPCON with Halden’s pressure measurements • Calculate the FGR for all four rods modelled • Secondary Objective: Assess the accuracy of the Modified Forsberg-Massih FGR model in FRAPCON for chromia doped pellets • NOTE: found problem with variable axial node lengths and axial zoning –under investigation FRAPCON/FRAPTRAN User Group Meeting

  4. Presented at EHPG September 11, 2014 IFA-716Analytical Methods & Results • Adjusted rod plenum length to match initial rod internal volume FRAPCON/FRAPTRAN User Group Meeting

  5. Presented at EHPG September 11, 2014 IFA-716Analytical Methods & Results • Initial calculation used default FRAPCON-3.5 options, where a 10 μm grain size is hard-wired in the code for the modified Forsberg Massih FGR model • Poor agreement with Halden data • Modified the code so that GRNSIZE was actually read and used by the subroutine • Much better agreement with the Halden data FRAPCON/FRAPTRAN User Group Meeting

  6. Pre-decisional work submitted to JNM for publication on September 10, 2014 Cladding Stress in Spent Fuel During Extended Dry Storage • NRC has performed a study of cladding stress in spent nuclear fuel (SNF) for a 300 year period of dry storage • This work is part of the ongoing research effort for Extended Storage and Transportation (EST) • GOAL: to assess the potential for low temperature creep (LTC) and delayed hydride cracking (DHC) failures • FRAPCON developments to support this work: • FRAPCON-DATING • Cladding creep in storage at the end of irradiation • Calculation based on rod internal pressure or specified cladding stress, and temperature decay curve for helium cooling, nitrogen cooling, or user-specified • FRAPCON-SFMOD • FRAPCON-3.5 with option to specify additional gas moles and additional fuel pellet swelling as a function of time FRAPCON/FRAPTRAN User Group Meeting

  7. Pre-decisional work submitted to JNM for publication on September 10, 2014 Dry Storage Cladding Stress:Scope and Methodology • 7 fuel designs with many different power histories (243 cases modeled) • Sequence modeled: • Reactor irradiation to 60 GWd/MTU • 5 years in wet storage • 300 years in dry storage • Potential sources of stress: • Decay gas production and release (from ORIGEN calculation) • Fuel pellet swelling during storage (from literature survey: best-estimate and upper-limit correlations developed) • FRAPCON-SFMOD • Stresses as a result of decay gas production/release and pellet swelling • Did not produce accurate creep strain predictions • FRAPCON-DATING • Cladding creep strain as a result of the stresses calculated with FRAPCON-SFMOD FRAPCON/FRAPTRAN User Group Meeting

  8. Pre-decisional work submitted to JNM for publication on September 10, 2014 Dry Storage Cladding Stress:Decay Gas and Fuel Swelling • Stress calculated with FRAPCON-SFMOD • Initial drop in stress due to rapid cladding creep (red lines: upper limit swelling, green lines: best-estimate swelling) • Pellet swelling saturates at 50 to 150 years • Stress increase after initial drop is primarily due to decay gas production • Stress reaches levels that could potentially result in hydride reorientation, but at times when hydrogen solubility and temperature are low • Resulting strains calculated with DATING code: • 0.44% - 0.50% for BWR • 0.72% - 0.95% for PWR BWR 10x10 PWR 17x17 FRAPCON/FRAPTRAN User Group Meeting

  9. Pre-decisional work submitted to JNM for publication on September 10, 2014 Dry Storage Cladding Stress:Critical Crack for DHC • DHC critical flaw size calculated assuming KIH=5 MPa√m (conservative value) • Assuming existing flaw of 120μm (conservative) • Critical flaw size becomes smaller than the existing flaw size after 292 and 264 years of storage for BWR9x9 and BWR 10x10 cladding, respectively • For other designs (BWR8x8, PWR14x14, PWR15x15, PWR16x16, PWR17x17), the critical flaw size exceeds the size of any expected flaw for the 300 year period of dry storage FRAPCON/FRAPTRAN User Group Meeting

  10. To be discussed at OECD/NEA WGFS meeting September 2014 OECD/NEA RIA Benchmark Phase 2FRAPTRAN without FRAPCON • 8 stylized RIA cases • 3 coolant conditions: NSRR capsule, PWR hot zero power, BWR cold zero power • Gap vs. no gap, sliding vs. no sliding contact • 2 different power pulses • 2 different rod pressures • No FRAPCON initialization • Most cases ran well (6/8) • FEA model was used for sliding contact case only • Problems encountered • Cannot specify no spring (non-zero but negligible values were used) • BWR cold zero power did not converge easily • Problem with specifying zero flow was identified (very low flow specified instead) • For higher powered pulse, ballooning predicted, as well as boiling crisis • Injected energy continued to increase after pulse: could be error or due to metal water reaction • Very high temperatures predicted… • Code-to-code comparison results will be discussed later this month at OECD/NEA WGFS meeting FRAPCON/FRAPTRAN User Group Meeting

  11. Presented at WRFPM 2014 Fuel Dispersal Predictions with FRAPCON/TRACE/FRAPTRAN FRAPCON/FRAPTRAN User Group Meeting

  12. Presented at WRFPM 2014 Fuel DispersalModeling Strategy • Steady-state fuel performance: FRAPCON • PWR coolant temperatures from TRACE • Initialization parameters for TRACE steady-state calculation • Initialization parameters for FRAPTRAN transient calculation • Steady-state systems thermal hydraulics: TRACE • FRAPCON steady-state initialization • Initialization parameters for TRACE transient calculation • Transient systems thermal hydraulics: TRACE • TRACE steady-state initialization • Initialization parameters for FRAPTRAN transient calculation • Transient fuel performance: FRAPTRAN • FRAPCON steady-state and TRACE transient initialization Steady-State FRAPCON TRACE Transient TRACE FRAPTRAN FRAPCON/FRAPTRAN User Group Meeting

  13. Fuel DispersalCode Problems and Fixes • Gamma heating was not taken into account in FRAPCON and was a constant in FRAPTRAN • Gamma heating for FRAPCON: user-input OR default values for PWR and BWR, based on neutronic calculations performed by Ian Porter (journal article under review) • Will be in next version of FRAPCON • Updated gamma heating for FRATRAN: user-input OR correlation based on coolant density (based on 17x17 PWR fuel, to be verified for other designs) • Will be in next version of FRAPTRAN • Core coolant temperatures are relative uniform for PWR, but single rod cod predicts cladding temperature assuming no mixing and no cross flow, and no ΔP taken into account • Over prediction of temperatures, corrosion, FGR, etc. for high power rods, and under prediction for low power rods • New ability to specify coolant temperature and pressure • Noticed some problems with FRAPCON gap printout • Gap calculation for printout based on OD cladding displacement, instead of ID displacement • Will be fixed in next version of FRAPCON • Printouts for fuel strain: thermal, densification, swelling, and relocation • New printouts for cladding : ID and OD displacement FRAPCON/FRAPTRAN User Group Meeting

  14. Fuel DispersalFRAPCON/FRAPTRAN Developments • Code modernization performed to date • FRAPCON: fully upgraded to F90 files, no more common blocks, fully dynamic arrays • FRAPTRAN: fully upgraded to F90 files, no more common blocks • Code modernization in progress • Removal of unused code • Migration to FORTRAN 95: • Full conversion to modules, no implicit variables, no include statements, use of PARAMETER statements, 120 character lines, etc… • Reduce the need for compiler options to make codes more portable • Logic improvements when practical (CASE SELECT, GOTO, etc…) • Dynamic dimensioning in FRAPTRAN • Develop guidelines for future programming • Coupling of FRATRAN and TRACE • Tested for 1 fuel rod and 1 heat structure: seems to work well • Developed but not yet fully tested for larger TRACE model with more than 1 heat structure • 1 TRACE run in parallel with many FRAPTRAN runs • Coupling based on dynamic pointers FRAPCON/FRAPTRAN User Group Meeting

  15. Fuel DispersalItems for Future Investigation • Fuel rod ruptures predicted during quench for LBLOCA • Burst strain and balloon length have a large impact on fuel dispersal predictions, but relatively large uncertainty on these predictions, particularly balloon length • Look into modeling potential effects of grid spacers on thermal and mechanical response • Look into pros and cons of modeling grid spacers in FRAPCON FRAPCON/FRAPTRAN User Group Meeting

  16. Others Items of Interest • New tools: • DOXYGEN for documentation • GIT for version control • Possible interface for users in the future, but not yet decided • Both tools also used for BISON development • Beta versions • Future code documentation • Back-compatibility • Old versions for download • Users’ suggestions? FRAPCON/FRAPTRAN User Group Meeting

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