Development of an improved quasi-static transient analysis code based on three-dimensional Sn nodal transport theory for fast reactor

A transient analysis code based on three-dimensional Sn nodal transport theory was developed for accurate transient analysis of the fast reactor. The time-dependent flux is factorized into the amplitude function and the shape function by the improved quasi-static approximation. The direct extension of the Sn nodal transport theory leads to the angular-dependent source term and requires much computer memory. To avoid direct treatment of angular-dependent source term, a new treatment was derived for the source term. The results of steady-state calculations were compared with that obtained by NSHEX for the verification of transport solver. For the verification of reactivity calculation based on perturbation theory, the reactivity was compared with that obtained from the multiplication factor by using the adiabatic approximation. The result with Sn transport calculation was compared with that with the diffusion calculation in Monju core. The results show the discrepancy of reactivity mainly comes from the absorption term.