Study on variance reduction technique based on adjoint Discrete Ordinate method

For deep-penetration shielding calculation, Monte Carlo (MC) method requires simulating a great number of particles to obtain reliable results, thus huge amount of computation time is the main problem of the MC method. Source biasing and weight window technique effectively decrease the tally error of deep-penetration problem. This paper studies variance reduction techniques (VRTs) based on adjoint fluence rate from a Discrete Ordinate (SN) code JSNT, generates source biasing factors and weight window parameters for a MC code JMCT, develops source sampling subroutine for JMCT, and verifies the VRT on measurements, finally applies the VRT to reactor pressure vessel fast neutron fluence rate and cavity neutron and photon dose rate calculation. Numerical results show that the VRT increases calculation efficiency by 1-2 orders for deep-penetration shielding calculation with high precision compared with unbiased MC method.