FRAPCON-3/FRAPTRAN APPLICATIONS Unit of Nuclear Safety Research CIEMAT ACTIVITIES on FRAPCON-3/FRAPTRAN APPLICATIONS (2014-2015) Unit of Nuclear Safety Research Division of Nuclear Fission CIEMAT-Madrid Spain

MAIN ACTIVITIES UA Steady state (CNAT) Power ramp (NEA) FRAPCON-3 FRPCN-3xt RIA (CSN/NEA) LOCA (CSN/HALDEN) FRAPTRAN Dry storage (ENRESA/ESCP) 2

STEADY STATE POWER RAMP Activity: Verification of safety analyses on PWR fuel performance (Trillo NPP) Code: FRAPCON-3.5 Outcomes: ongoing POWER RAMP Activity: Assessment of codes to simulate PCMI during ramps (NEA benchmark) Code: FRAPCON-3.5 Outcomes: ongoing 3

RIA Activity: Assessment of codes to simulate RIAs (NEA bnchmrk II) Code: FRAPTRAN-1.5 10 postulated cases - fresh fuel Remarks: Special attention should be paid to clad-to-coolant heat transfer model, particularly for BWR conditions Considering the large cladding temperature gradient under RIA conditions the validity of the thin wall approach used in the mechanical module would be worth to be revised The results highlight that the gap closure/reopening has strong influence in thermal-mechanical predictions. For instance, an unexpected fuel relocation contribution of the initial gap was detected and corrected by the NRC 4

LOCA Activity: Assessment of codes to simulate LOCAs (Halden tests) Code: FRAPCON-3.5+FRAPTRAN-1.5 (v1.4 also used in PWRs) IFA-650.5, .3, .10 (PWR) & IFA-650.7, .12 (BWR) Preliminary remarks: Outer cladding temperature shows moderate deviations from data (HTCs were imposed) PIE data are scarce to assess oxide modeling (protective and non-protective options) Cladding elongation at failure time shows substantial deviations from data in v1.5 (BALON2 modifications) 5

DRY STORAGE Activity: Extension of FRAPCON-3.5 to dry storage conditions (ENRESA) 6

DRY STORAGE Focus: Cladding performance – Vertical cask FRAPCON-3xt can predict long storage cladding T If DBTT is known, t-to-DBT estimations can be done 7

Uncertainty analysis. RIA Activity: Impact of steady state uncertainties on RIA modeling (CSN) Code: FRAPCON-3.5 (→SCANAIR) Scenario: Realistic case - Irradiated fuel (PWR, 68.5 GWd/tU) - Power pulse (99 cal/g, 32 ms) Sensitivity analysis Order statistics Failure prediction can be improved by: Enhancing FRAPCON-3 models affecting oxide thickness prediction, specially the oxide conductivity model Ensuring an accurate characterization of the gap width at the beginning of the transient Top Fuel 2015 8

Uncertainty analysis. Dry storage Activity: Uncertainty calculation of PEOL as DS initial condition (ENRESA/ESCP) Code: FRAPCON-3.5 Scenario: Zry-4 fuel rod (65 GWd/tU) UA: Monte Carlo based on deterministic reduction NUREG-1754 If uncertainties were accounted for, it would be difficult to analyse the power history effect Upper bound predictions would allow estimating conservative stresses at DS onset Top Fuel 2015 9

THANK YOU FOR YOUR ATTENTION 10

RIA Cases 5 and 7: Fresh fuel - Triangular power pulse (127 cal/g , 30 ms) 11

LOCA PWR (61 GWd/tU) 12