BERMUDA-2DN: a two-dimensional neutron transport code

A two-dimensional neutron transport code BERMUDA-2DN has been developed from the one-dimensional code PALLAS-TS (BERMUDA-1DN). The purpose of the present code is to analyze the fusion blanket neutronics experiments for plane or cylindrical assemblies, and to establish a basis of an accurate shielding analysis system for fusion and fission reactors. The time-independent transport equation is solved for two-dimensional, cylindrical, multi-regional geometry using the direct integration method in a multigroup model. In addition, group-angle transfer matrices are accurately obtained from the double-differential cross section data, without the Legendre polynomial expansion, but with the energy and scattering angle correlation. As to group constants, user is able to choose a 120-group or a 46-group library. For angular discrete ordinates, a set of 40 points is fixed over the hemisphere drawn by unit direction vectors. Not only latitudes but also longitudes (as the boundaries of the angular regions on the unit sphere) are taken into account for the calculation of the group-angle transfer matrices. For the fixed point source located at the origin of (r,z) coordinates, the uncollided flux is obtained at each spatial mesh point using the usual point kernel. The transport equation is solved for the first collision source from the uncollided flux plus the slowing down source from upper groups. Thus, the angular flux distribution is obtained as the sum of the solution and the uncollided flux values. At an intense D-T neutron source FNS, measurements were performed on the angular dependence of leakage spectra from Li2O slab assemblies. The present code has been tested by analyzing the measured spectra. The results have shown to represent fairly well the observed values. (author)