Code Benchmark of Pressurized Conduction Cooldown Transient in the High Temperature Test Facility

Three system codes SAM, RELAP5-3D, and GAMMA+ were used to model the Pressunzed Conduction Cooldown (PCC) benchmark problem within the scope of the Organisation for Economic Cooperation and Development Nuclear Energy Agency (OECD/NEA) Thermal Hydraulics Code Validation Benchmark for High-Temperature Gas-Cooled Reactors using HTTP Data. The three different modeling methodologies are described, and results are used in code-to-code comparison. In steady-state operating condition;, good agreement was found for major parameters such as coolant temperature solid temperature and flow distribution. In PCC transient, all three codes predict thai natural circulation is several orders of magnitude lower than steady-state flow rate and core-wise heat transfer is therefore dominated by thermal conduction and radiation. The codes predict similar temperature trends in the solid structures but there are large discrepancies in the transient behavior. This is not surprising considering the vastly different modeling schemes of a very complex core geometry. The code-to-data phase of the benchmark could provide more insight into the dLrepancies and help to improve the system codes models.