ENERGY-ANGLE DEPENDENT NEUTRON SOURCE IN DETERMINISTIC TRANSPORT CODES WITH SPHERICAL HARMONIC EXPANSION

摘要

The use of Accelerator Driven Systems (ADS) is widely considered for transmutation of long living radioactive nuclides and thereby relieving to some extent the end of cycle waste repositories. The simulation of the ADS performance necessitates the use of deterministic solvers in particular as far as a transient analysis is concerned. One of the most important components which affect the system behavior considerably is the external neutron source. The importance of simulating this source adequately is therefore evident.In this study we analyze the neutron source implementation in deterministic codes. We introduce a general procedure for the energy-angle dependent neutron source in which the sensitivity to the energy group number and the Legendre order is illuminated. By means of MCNP reference calculation we show that a very high Legendre order (28) is needed for a precise spherical harmonic expansion, but with the common usage of order 5 a certain inaccuracy is inevitable if the number of the energy groups is realistic (5-6 fast groups).Further, we realized to transfer a specific neutron source representation from one coordinate system to another coordinate system in another code with a limited Legendre order. For higher orders additional work has to be done.