ARES is a multi-group of anisotropic scattering transport shielding code based on discrete ordinates method. The 3D radiation transport benchmark problems proposed by Kobayashi were calculated by ARES with sub-module ARES_RayEffect which using first collision method for ray effects mitigation. ARES_RayEffect calculates uncollided flux and first collision source moments for ARES. The uncollided flux is obtained by a ray tracing calculation between a source point and a target mesh center. In addition, ARES_RayEffect has a modifying factor function to improve the quality of uncollided flux calculation. For verification, the results of MCNP code are used as reference solution and the results of TORT with FNSUNCL3 are compared. ARES_RayEffect introduced the modifying factor to reduce the relative difference of meshes near the source region. For example, at the position (15,15,15) in Problem 1 case i, the relative difference of the result of ARES with ARES_RayEffect is −2.34%, while relative difference of the result of TORT with FNSUNCL3 is −11.92%. The calculated total neutron fluxes show good agreement with the MCNP solutions. For the pure absorber cases, the maximum differences are less than 3%. For the half scattering cases, the maximum differences are less than 11%. Numerical results demonstrate that ray effects can be effectively mitigated.

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Abstract：Ray effects are the inherent problem of 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 analytical method and discrete ordinates method respectively. In this article, RAY3D is valida ted by the Kobayashi benchmarks and applied to the neutron beamline shielding problem of China Spallation Neutron Source (CSNS) target station.Numerical results of the Kobayashi benchmarks indicate that DONTRAN3D with RAY3D solutions 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 CSNS target station neutron beamline shutter model. RAY3D can effectively mitigate ray effects and obtain relatively reasonable results.