Neutronics Analysis of Shielding Performance for VNS Inboard Toroidal Field Coil with Various Material Options

The Volumetric Neutron Source (VNS) is a crucial facility for the engineering validation of breeder blanket systems, which are critical components of future demonstration power plants (DEMOs). In a compact tokamak device such as the VNS, the inboard region has extremely limited radial space, making the design of a highly efficient shielding system a key challenge that determines the device’s lifetime and performance. This system must protect the superconducting toroidal field coils (TFCs) from neutron and gamma radiation. In particular, degradation of the epoxy-resin insulation due to radiation is a primary factor limiting the lifetime of the magnet system. This study conducts a comparative analysis of the shielding performance of various candidate materials within the VNS inboard shield blanket and vacuum vessel using MCNP6.3 with a three-dimensional computer-aided-design–derived model of the VNS. The key performance indicators are the neutron flux and nuclear heating density in the first TFC winding pack layer and the absorbed dose in the TFC epoxy insulator.