Application of the first collision source method to CSNS target station shielding calculation

Ray effects are an inherent problem of the discrete ordinates method. RAY3D, a functional module of ARES, which is a discrete ordinates code system, employs a semi-analytic first collision source method to mitigate ray effects. This method decomposes the flux into uncollided and collided components, and then calculates them with an analytical method and discrete ordinates method respectively. In this article, RAY3D is validated by the Kobayashi benchmarks and applied to the neutron beamline shielding problem of China Spallation Neutron Source (CSNS) target station. The numerical results of the Kobayashi benchmarks indicate that the solutions of DONTRAN3D with RAY3D agree well with the Monte Carlo solutions. The dose rate at the end of the neutron beamline is less than 10.83 μSv/h in the CSNS target station neutron beamline shutter model. RAY3D can effectively mitigate the ray effects and obtain relatively reasonable results.