Resolution of the direct containment heating issue for all Westinghouse plants with large dry containments or subatmospheric containments

Analysis of likelihood of lower head failure and ex-vessel fuel coolant interaction energetics for AP1000

“…In the MAAP calculation, the Zr oxidation fraction was estimated to be about 0.3, which is relatively low. For the high-pressure scenarios considered as part of the NRC direct containment heating (DCH) issue resolution for pressurized water reactors (Pilch et al, 1996), the most probable Zr oxidation fraction was about 0.4, and lowest value was 0.2 with an upper bound was about 0.6. Even though the high-pressure scenario condition is not directly relevant to this study, nevertheless, it is being referenced to show the range of uncertainties that have been considered in recent years and for previous studies.…”

An Evaluation Methodology Development and Application Process for Severe Accident Safety Issue Resolution

“…The credibility of an evaluation methodology relies on the associated verification and validation through code [8] (2) Core melt progression (i) Zr melt breakout temperature (ii) Fuel rod collapse temperature (iii) Core material melt temperatures PHEBUS (CEA) [9,10] QUENCH (FZK) [12] LOFT (OECD) [13] (3) Core melt relocation to lower head (i) Melt relocation heat transfer coefficient Lower head failure program (NRC) [14] (4) In-vessel oxide/metal separation RASPLAV/MASCA (OECD) [ [21] TROI (KAERI) [22] (10) High pressure melt ejection (i) Particle size (ii) Obstructions DCH/TDS/LFP/WC (SNL) [23][24][25][26][27] IET-Zion/IET-surry/U (SNL/ANL) [28,29] CWTI (ANL) [31] DCH (FAI) [32] (11) Steam/hydrogen transport (i) Containment transition to single convective volume HDR (Germany) [33] NUPEC large scale test facility (MITI, Japan) [34] Battelle model containment (USA) [35] (12) Hydrogen recombination (i) PAR efficiency…”

“…Supplemental analyses should be performed to complete or complement the best-estimate analysis of the relevant scenarios and the uncertainty analysis. Of particular note are analyses for containment failure probability from HPME and fuel-coolant interactions (both in-and ex-vessel) using parametric models applying methodologies similar to [75]; combustion loads; source term; selected low-frequency, high-consequence events. Inputs required for these studies can usually benefit from extracting bounding values presented in the uncertainty analysis results.…”