Computation of continuous-energy neutron spectra with discrete ordinates transport theory

A procedure is presented to obtain a continuous-energy representation of the neutron spectrum using one-dimensional discrete ordinates calculations with a combination of multigroup (MG) and pointwise (PW) nuclear data. This provides the capability of determining the fine-structure energy distribution of the angular flux and flux moments within the resonance range as well as the smoother spectrum in the high- and thermal-energy ranges. A new method called a submoment expansion is developed to accurately calculate the Legendre moments of the elastic scatter source for the PW transport calculation, and the coupling between the MG and PW calculations is discussed in detail. The continuous-energy flux spectra can be utilized as problem-dependent weighting functions to process self-shielded MG cross sections for reactor physics and/or criticality safety analysis. This calculational method has been implemented in a new PW transport code called CENTRM that can be executed as a module in the AMPX and SCALE computer code packages. An example application using ENDF/B-VI cross-section data to analyze critical benchmarks is presented.