An Investigation of the Effects of Water Content on the Shielding Performance of the Primary Upper Shield in the High Temperature Engineering Test Reactor (HTTR)

Abstract

High Temperature Engineering Test Reactor (HTTR) is the first High Temperature Gas-cooled Reactor in Japan. The plant layout and radiation shielding are designed so that the plant can be operated without any employee receiving a high radiation dose rate. The primary upper shield of HTTR is composed of concrete (grout) and carbon steel. The function of the primary upper shield is to attenuate neutrons and gamma rays generated in the core to satisfy dose rate criterion for the operating floor. Since the HTGR uses high temperature helium as coolant, temperatures of shielding materials could be higher than that of conventional reactors. According to the analytical simulation, the maximum temperature inside of the primary upper shield during full-power operation was estimated to be about 85 °C. Since water content in the primary upper shield concrete depends on its temperature, shielding performance of the concrete under HTTR operational conditions need to be confirmed. Thus the water content of the concrete was experimentally investigated by out-of-pile heat-up tests to 175 °C. According to these tests, a water release model was developed. The out-of-pile heat-up tests showed that the water content in the concrete was larger than 78 kg/m3 up to 110 °C in a 95 % confidence limit.