Density-extrapolation Global Variance Reduction (degvr) Method for Large-Scale Radiation Field Calculation.

The lack of a universal and effective Global Variance Reduction (GVR) method for the deep-penetration Monte Carlo calculation makes it difficult or impossible to calculate the radiation field of large nuclear facilities. We propose a Density-extrapolation Global Variance Reduction (DeGVR) method for the large-scale radiation field calculation. After reducing the density of all materials to avoid the deep penetration problem, two global flux distributions of the two different material densities are obtained with two fixed-source calculations, and then the global flux distribution of the original material density is obtained by extrapolating the two global flux distributions. The global flux distribution of the original material density is then used for global variance reduction. In a large-scale model with a flux attenuation of 1080, the DeGVR method only takes 40.3 minutes to build the radiation field, improves the Average Figure-of-Merit (AV.FOM) up to 85652 times and the counting rate per time (CRPT) up to 88107 times compared with the standard Monte Carlo method. In addition to the high efficiency, the DeGVR method has high universality and robustness because it constructs the global information in a clever way that does not rely on the complex mathematical derivation and geometric modeling. The DeGVR method shows excellent application potential in large-scale radiation analysis.