Validation of Evaluation Model for Thermal Absorber System in High Temperature Gas-Cooled Reactor Nuclear Hydrogen Production System

Abstract

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 an air cooler 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 analytical model for a thermal absorber 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 air cooler cooled by ambient air. Experimental data obtained from a mock-up test facility of thermal absorber is compared with calculated results of the developed model.

As a results of the comparative study, the code reproduced similar tendency in the transient thermal hydraulic behavior in the thermal absorber during the loss of chemical reaction test. The code also conservatively evaluated the variation in the helium gas temperature at the outlet of the steam generator from the initial condition compared to that observed in the test results. In conclusion, the system analysis code was validated for the application to the thermal absorber using the results of loss of chemical reaction test in the mock-up test facility.