Shielding technology for upper structure of HTTR

Ueta, Shohei   ; Sakaba, Nariaki ; Sawa, Kazuhiro

In the shielding design for the High Temperature Gas-cooled Reactor (HTGR), special attentions shall be needed to avoid neutron streaming, since helium gas as a coolant does not work for shielding. Japan Atomic Energy Agency has demonstrated the performance of shielding through testing operations of the High Temperature Engineering Test Reactor (HTTR) in order to establish design method for shielding of the Very-High-Temperature Reactor (VHTR) as a Generation-IV nuclear power system. As results of the test, it was confirmed that dose equivalent rates for neutron and -ray at on-operating acceptable areas were less than detection limit and as low as background, respectively. The measured dose at the stand-pipe room corresponded to the detection limit, and it was found that over 90% of dose derived from fast neutron. It was indicated that there was still a margin of factor 50 in addition to the design which excluded the safety factor. The measured dose rates showed good agreement with the predicted considering the control rod withdrawing effect. The knowledge on the design method and the demonstration of shielding by the HTTR will strongly contribute to realizing and optimizing the designs of future VHTRs.