Monte Carlo calculation of the neutron and gamma-ray distributions inside the LHD experimental building and shielding design for diagnostics

Abstract

On the Large Helical Device (LHD), deuterium plasma experiments began in March 2017. In the plasma control, plasma heating and diagnostic systems, radiation sensitive components such as a programmable logic controller (PLC) and CCD sensors are commonly used. Three-dimensional distributions of neutron and gamma-ray in the LHD experimental building have been calculated by Monte Carlo code MCNP6 with the nuclear data library of ENDF B-VII.1 to prove the precise information on the radiation field and to introduce a countermeasure to the radiation. The total neutron flux in the torus hall of LHD is ~109 n/cm2•s for the maximum neutron yield shot. The total neutron and gamma-ray fluxes in the basement are 1-2 order smaller than those in the torus hall, which is due to the streaming through penetrations in the floor concrete slab. The shielding design for the compact neutral particle analyzer (CNPA) is also carried out. It is found that 10% borated polyethylene thicker than 15 cm is necessary for the shield in all directions.