Design and validation of shielding for a neutron generator using MCNP6

Abstract

This study presents the design, fabrication, and experimental validation of a shielding facility for the DD-108 neutron generator installed for active neutron interrogation applications such as differential die-away analysis. The shielding structure was optimized using MCNP6 simulations to meet regulatory dose limits of 20 mSv/y for radiation workers and 1 mSv/y for the general public. The regulatory dose limits were achieved by utilizing the existing concrete and lead structures and designing additional high density polyethylene shielding based on neutron and photon dose assessments. Various effective dose conversion coefficients were considered to ensure a conservative evaluation. The facility was constructed, and calibrated dosimeter measurements confirmed that neutron and photon doses were up to 50 % and 76 % lower than simulation predictions. These results reflect the conservative assumptions applied in the modeling, ensuring robust safety margins. The shielding facility met all licensing requirements, leading to the first regulatory approval of a DD-108 neutron generator in South Korea. This validation demonstrates the practicality of MCNP6-based shielding design and provides valuable insights for future neutron generator shielding applications.