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:
FRAPCON/FRAPTRAN
User Group Meeting September 18, 2014

2. U.S. NRC Research 2014 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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

3. IFA-716 Background and Objectives
Presented at EHPG September 11, 2014
IFA-716 Background 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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

4. IFA-716 Analytical Methods & Results
Presented at EHPG September 11, 2014
IFA-716 Analytical Methods & Results
Adjusted rod plenum length to match initial rod internal volume
Test Rod
IFA­716
rod 1
rod 2
rod 5
rod 6
Measured rod free volume (cm3)
5.80
5.95
5.90
6.00
Measured Plenum Length (mm)
40.80
41.10
41.40
FRAPCON calculated rod free volume for measured plenum length (cm3)
4.34
4.31
4.10
4.33
Adjusted plenum length (mm)
66.79
69.89
72.99
70.75
FRAPCON calculated rod free volume for adjusted plenum length (cm3)
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

5. IFA-716 Analytical Methods & Results
Presented at EHPG September 11, 2014
IFA-716 Analytical 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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

6. Cladding Stress in Spent Fuel During Extended Dry Storage
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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

7. Dry Storage Cladding Stress: Scope and Methodology
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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

8. Dry Storage Cladding Stress: Decay Gas and Fuel Swelling
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% % for BWR
0.72% % for PWR
BWR 10x10
PWR 17x17
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

9. Dry Storage Cladding Stress: Critical Crack for DHC
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
Fuel Design
Normalized flaw size at 120 μm
Time to reach 120 μm critical flaw size (years)
Temperature at 120 μm critical flaw size (K)
Stress at 120 μm critical flaw size (MPa)
BWR 8x8
0.1476
>300
<370
>205
BWR 9x9
0.1688
292
375
200
BWR 10x10
0.1818
264
385
195
PWR 14x14
0.1628
>175
PWR 15x15
>155
PWR 16x16
0.1890
>165
PWR 17x17
0.1967
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

10. OECD/NEA RIA Benchmark Phase 2 FRAPTRAN without FRAPCON
To be discussed at OECD/NEA WGFS meeting September 2014
OECD/NEA RIA Benchmark Phase 2 FRAPTRAN 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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

11. Fuel Dispersal Predictions with FRAPCON/TRACE/FRAPTRAN
Presented at WRFPM 2014
Fuel Dispersal Predictions with FRAPCON/TRACE/FRAPTRAN
Experimental Research
Fuel rod rupture conditions
Fuel relocation conditions
Burnup dependent particle size distribution
ANL, Halden and Studsvik LOCA research, documented elsewhere
Fuel dispersal predictions
Number, timing, and location of fuel rod ruptures during a LOCA
Fuel rod characteristics at and near rupture
Estimation of dispersed fuel based on experimentally determined thresholds
Consequence analysis
Based on quantification and characterization of dispersed fuel
Prediction of thermal hydraulic and radiological consequences
Future analytical work
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

12. Fuel Dispersal Modeling Strategy
Presented at WRFPM 2014
Fuel Dispersal Modeling 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
Transient fuel performance: FRAPTRAN
FRAPCON steady-state and TRACE transient initialization
Steady-State
FRAPCON
TRACE
Transient
TRACE
FRAPTRAN
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

13. Fuel Dispersal Code 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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

14. Fuel Dispersal FRAPCON/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
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting

15. Fuel Dispersal Items 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
18 September 2014
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?
18 September 2014
FRAPCON/FRAPTRAN User Group Meeting