Thermal-hydraulic analyses of overcooling sequences for the H. B. Robinson Unit 2 pressurized thermal shock study

For each sequence, reactor vessel downcomer fluid pressure and temperature histories were required for the two-hour period following the initiating event. Analyses previously performed at the Idaho National Engineering Laboratory (INEL) fully investigated a limited number of the sequences using a detailed RELAP5 model of the H.B. Robinson, Unit 2 (HBR-2) plant. However, a full investigation of all sequences using the detailed model was not economically practical. New methods were required to generate results for the remaining sequences. Pressure and temperature histories for these remaining sequences were generated at the INEL through a process combining partial-length calculations using the detailed RELAP5 model, full-length calculations using a simplified RELAP5 model, and hand calculations. This report documents both the methods used in this process and the results. The sequences investigated contain significant conservatisms concerning equipment failures, operator actions, or both.