The Adjoint Coarse Mesh Transport (COMET) Method and Reciprocity Relation of Response Coefficients

Abstract

ABSTRACTAn efficient response-based adjoint radiation transport method is developed and implemented into the coarse mesh transport (COMET) code. The numerical implementation of the adjoint COMET consists of three steps: local calculations to compute adjoint response coefficients for each unique coarse mesh, global calculations to converge on the core eigenvalue and adjoint partial current moments crossing coarse mesh boundaries, and local construction of the adjoint flux distribution within each coarse mesh. The reciprocity relations between forward and adjoint response functions are also derived. This unique property can be used to compute adjoint response coefficients without solving the local adjoint problems directly. As a result, the computational effort to generate adjoint response coefficients is completely avoided. The adjoint COMET is tested for two applications: adjoint whole-core eigenvalue calculations in the 3D C5G7 benchmark problem, and local calculations of adjoint surface-to-volume fission density response coefficients for a stylized CANDU benchmark problem. These tests have shown that the adjoint COMET method is significantly faster than the Monte Carlo method while maintaining accuracy close to that of Monte Carlo.