Neutron Transport Modeling for the Design of WHAM VNS

A compact, high flux volumetric neutron source (WHAM VNS) is being designed as a successor to the Wisconsin HTS Axisymmetric Mirror (WHAM) experiment. Because initial analysis revealed that a pair of shielded REBCO coils with radius of 45 cm would be damaged by fast neutrons within days of full-power operation, neutron shielding requirements for the HTS magnets is expected to constrain minimum device size. Therefore, CQL3D simulations were utilized to generate realistic VNS models with a target of 5 × 10¹⁷ ​n/s DT source rate expected from the experiment. This model was then used for the optimization of shielding geometry and material for a range of magnet sizes with a parameterized model built in OpenMC. Additional factors such as nuclear heating, long-term material damage, fast neutron activation of structural materials and access to locations of peak flux for fusion material testing were considered. Scenarios allowing for operation for more than 10 full-power years have since been identified with peak fast neutron flux at the first wall reaching 5 × 10¹³ n/cm²s. A preliminary design for a tritium-breeding blanket is also being developed in conjunction with the neutron reflecting shield.