Monte Carlo-based assessment of neutron and secondary gamma doses in a deuterium-tritium (D-T) neutron generator facility

Abstract

Computational evaluation using Monte Carlo simulations is usually employed to determine if a neutron source facility meets the standards for safe operation and protection against ionizing radiation. In this work, a laboratory with a deuterium-tritium (D-T) fusion-based neutron generator (NG) was modeled, and the spatial neutron and secondary photon dose distributions were calculated using the PHITS Monte Carlo transport code. Simulations were performed using mesh tallies along the xy, xz, and yz planes with 30 spherical region tallies serving as air detectors in strategic locations. The west-facing NG is the optimal position during operation. For a 500-hour annual operating time, the counting room doses are acceptable with respect to occupational dose limits. However, additional shielding is necessary to lessen doses in the work area. Borated polyethylene was determined to be the most effective shielding around the D-T NG such that the total dose to staff and operators is within the annual limit of 20 mSv. To provide guidance on possible emergency situations, scenarios in which the NG is left running when the moderator assembly is altered were also evaluated.