Calculational problem for deep penetration of neutrons through a one-bend sodium duct

This problem features a two-dimensional geometry representing a sodium duct surrounded by concrete that can easily be modeled with both Monte Carlo and two-dimensional S/sub N/ codes. The neutron source is placed on an external duct surface, has a uniform spectrum over the energy range of 5 to 2 MeV, and is forward peaked with a cosine distribution. The average distance covered by a neutron leaving the duct surface at the exit is about 360 cm. The importance sampling method of the Monte Carlo code TRIPOLI-2 is used. Fluxes and detector responses are tabulated for several surfaces defined along the neutron path in the sodium. A population of approximately 5000 neutrons undergoes about one million collisions giving flux and current at the duct exit with a standard error of 7.5%. 3 figures, 6 tables