Assessment of irradiation temperature stability of the first irradiation test rig in the HTTR

The High Temperature Engineering Test Reactor (HTTR) can provide very large irradiation spaces at high temperatures for various irradiation tests. The first irradiation test rig for the HTTR, the I–I type irradiation equipment, was developed for an in-pile creep test on a stainless steel with large standard size specimens. The equipment uses the ambient high temperature of the core for the irradiation temperature control. The target irradiation temperatures are 550 and 600 °C with the target temperature deviation of ±3 °C. In this study, the specimen temperature stability at the irradiation test was assessed by both analytical and experimental approaches. The irradiation temperature changes at transient conditions were analyzed by a finite element method (FEM) code and the temperature controllability of the equipment was examined by a mockup test. The controllability was evaluated with the measured temperature transient data at the core graphite components in the Rise-to-Power tests of the HTTR. The result indicates that the temperature control method of the I–I type irradiation equipment is effective to keep the irradiation temperature stable in the irradiation test.