A Collision Probability and MOC-Based Lattice and Burnup Code for Analysis of LWR Fuel Assemblies

The BOXER3 code was developed in the Bhabha Atomic Research Centre during the 1980s as a three-dimensional code for the analysis of a pressurized heavy water reactor supercell containing fuel, moderator, and a reactivity device inserted perpendicular to the fuel channel, with options for carrying out calculations in a general two-dimensional geometry (infinite and homogeneous in one direction) and a one-dimensional plane geometry. Taking into account the computing resources available then, the code was run in few groups after obtaining condensed group cross sections for various materials from a one-dimensional multigroup calculation.

In this paper, we describe various developments carried out recently for enabling its use as an assembly-level lattice-burnup code. In addition to the collision probability method originally available, the method of characteristics for solving the multigroup transport equation has been added. This development permits the treatment of anisotropic scattering wherever necessary and available in cross-section libraries. Other developments include coupling of the code to the WIMS 69/172-group library, a method for the evaluation of the pin-dependent Dancoff factor, and the introduction of burnup. The transport equation in the collision probability method is cast in a form more suitable for iterations as well as for the method of renormalization of collision probabilities used in the work. The analysis of several benchmark problems has been carried out and the results obtained using the new code are presented.