Abstract
To investigate the safety design criteria of heat utilization system for the HTGRs, it is necessary to evaluate the effect of fluctuation of thermal load on the reactor. The nuclear heat supply fluctuation test by non-nuclear heating was carried out by devising a new test procedure to simulate the nuclear heat supply test which is carried out in the nuclear powered operation. The test data is used to verify the numerical code to calculate the temperature of core bottom structure to carry out the safety evaluation of abnormal events in the heat utilization system. In the test, while the helium gas temperature was heated up to 120 ℃ by compression heat of gas circulators, it is necessary to impose a sufficiently high disturbance in the reactor inlet temperature. However, there was a technical restriction in the heat release from final heat sink for cooling water freeze proofing during operation in winter, which is special to the low temperature non-nuclear heating test. As the results of improvement of test procedure, a sufficiently high temperature disturbance was imposed on the reactor inlet temperature. Thus, it was found that the response of temperatures of metallic components such as side shielding blocks was faster than those of graphite blocks in the core bottom structure. Such difference of temperature transient characteristics between the metallic core support structure and the graphite blocks was emerged. It was also found that the temperature response was significantly affected by the heat capacities of components, the level of imposed disturbance and heat transfer performance.
