Neutronic analysis of RSG GAS silicide core with uranium density of 4,8 g/cm3

Fuel conversion program of the RSG GAS multipurpose reactor is to convert the fuel from oxide, U3O8-Al to silicide, U3Si2-Al. The aim of the program is to gain longer operation cycle by having, which is technically possible for silicide fuel, a higher density. Since 1999, a core conversion program of the RSG GAS reactor from oxide to silicide fuel with the same fuel density of 2.96 g U/cm3 has been started and at the end of year 2002 all silicide core was achieved. However the conversion study of using higher uranium density fuel in the RSG GAS reactor is still on-going. The study is focused on silicide fuel with density of 3.55 gU/cm3, 4.8 gU/cm3 and 5.2 gU/cm3. Previous research showed that 3.55 g/cm3 uranium density can extend the operation cycle length from 615 MWD to 900 MWD significantly without any material and core configuration change. This paper presents an advanced research on the 4.8 g /cm3 uranium density utilization on RSG-GAS core. This research focused on the neutronic aspect, including reactivity balance, power peaking factor and kinetic parameters. The calculations were performed using computer codes WIMS/D4, Batan-2/3 DIFF and Batn-EQUIL-2D. During the design, the following constraints are used: 1. No major modification to the reactor balance of plant, shielding, core main structural components, and civil buildings may be made. 2. The number as well as the performance of irradiation positions and facilities must be maintained. 3. The existing one-stuck-rod reactivity margin and thermal-hydraulic safety requirements must be fulfilled. 4. Maximum discharge burn-up is limited to 70 % for licensing purposes. The calculations showed that the reactor cycle length can be extended until 1400 MWD with the maximum radial power peaking factor 1.31 less that the limit value of 1.4. However, the two safety rods should be added to higher the shutdown margin (one stuck rod criteria). The reactivity balance and the in-core fuel management of the core are also presented in this paper. For kinetic parameter, the calculated delayed neutron fraction, delayed neutron decay constant and average neutron life time are 7.03256 x 10-3, 7.8520 x 10-2 s-1 and 55.49 μs respectively. Those parameters are not changed, significantly, compared with the existing core. It is concluded that the proposed equilibrium silicide of 4.8 gU/cm3 core configuration could be applied in RSG-GAS operation, safely. (author)