Validation of dynamic analysis code for high temperature gas-cooled reactor connecting hydrogen production system with a heat removal fluctuation mitigation system

Hasegawa, Takeshi ; Aoki, Takeshi  ; Shimizu, Atsushi ; Sato, Hiroyuki  

Japan Atomic Energy Agency (JAEA) is planning a nuclear hydrogen production demonstration test by connecting a hydrogen production to the HTTR (High Temperature engineering Test Reactor), a 30MWt High Temperature Gas-cooled Reactor (HTGR) test reactor located at JAEA's Oarai Research Institute. The objective of the test is to establish coupling technologies between HTGR and a hydrogen production plant. One of key technologies to be developed is a thermal absorber consists of a steam generator and a radiator that can mitigate rapid fluctuations in helium temperatures during loss of heat load in the hydrogen production plant. The present study aims to develop an evaluation model for the absorber system that can be used for safety analyses of the HTTR for coupling a hydrogen production plant. A set of closed loop model is newly introduced to a RELAP5-based system analysis code to enable evaluation of steam-water natural circulation behavior between the steam generator heated by helium and the radiator cooled by ambient air. Experimental data obtained from a mock-up test facility of thermal absorber system is compared with calculated results of the developed model. As a results of the comparative study, it was confirmed that numerical analysis results were agreed well with experimental results. In conclusion, the proposed evaluation model is applicable for the safety analysis of a thermal absorber system to be deployed in HTGR hydrogen production systems.