Steady-State and Transient Simulations of Httr Using RELAP5-3D

Abstract

The (High Temperature Test Reactor) HTTR is a 30 MW helium-cooled, graphite-moderated experimental gas-cooled reactor (HTGR) developed, designed, constructed, and operated by the Japan Atomic Energy Research Institute (JAERI). A thermalhydrualics model for the HTTR was developed using the RELAP5-3D code. In the RELAP5-3D model, the HTTR core hydraulics are represented by 30 channel groups (one for each fuel column). The convective heat transfer in the core is modeled using 70 heat structures, and heat conduction among 30 fuel columns, 19 control-rod, 12 replaceable-reflector blocks, and one permanent reflector modeled using 10 conduction/radiation enclosures. The three loops included in the RELAP5-3D model are: 1) the primary He loop; 2) the Primary Pressurized Water Cooler (PPWC) H2O loop; and 3) the Air Cooler (AC) N2 loop. Both full-power (30MW) steady-state and LOFC transient simulations under 30% reactor power (9 MW) were performed using a built-in point kinetics model. The results have been compared with the available experimental data. It is demonstrated that the RELAP5-3D model is capable of reproducing the thermalhydraulic behavior of the reactor in both steady-state operation and transient accident conditions. More investigations are necessary to expand the model to include other loops in the HTTR plant, such as those for Auxiliary Cooling System (ACS), Intermediate Heat Exchanger (IHX), and Vessel Cooling System (VCS). Future investigations can include coupled Physics/Thermalhydraulics simulations.