A CANDU-6 In-Core Fuel Management Study on CANFLEX-RU Fuel

Abstract

In the CANDU 6 reactor, an 8-bundle shift refuelling scheme is currently employed in natural uranium (NU) fuel management. This refuelling scheme has difficulty in its use for the CANDU in-core fuel management of a 0.92 w/o RUFIC (Recovered Uranium Fuel in CANDU) fuel as a 0.90w/o-equivalent SEU fuel because of the reactivity increase. Considering that the discharge bumup of the RUIFC fuel is almost twice that of the NU fuel, a 4-bundle shift refuelling scheme is preferable for the in-core fuel management of the RUFIC fuel in the CANDU-6 reactor. In this paper, 700 full power day (FPD) equilibrium RUFIC core simulations have been carried out by the 4-bundle shift refuelling scheme in order to find the optimized refuelling schemes for CANDU-6 cores. The computer code system used for this work is WIMS-AECL/DRAGON/ RFSP/AUTOREFUEL. The results of the 700 FPD equilibrium core simulations with the 4-bundle shift refuelling scheme showed that the variation of the maximum channel power (MCP) and maximum bundle power (MBP) as a function of FPD are maintained within the self-imposed operating limits, which are currently employed in a Wolsong reactor. Maximum channel power peaking factor (CPPF) with the number of FPD was maintained below 1.11. It is also found that all the fuel element ratings are below the stress corrosion cracking (SCC) defect threshold curves for a normal operation and power boost, except that the boosted powers of the outermost ring elements are above the SCC threshold in the bumup range of around 100 MWh/kgU. Evaluating only the operating limits for MCP, MBP, CPPF, and the behavior of the liquid zone control system, it is concluded that the 4-bundle shift refuelling scheme is feasible for the equilibrium core fuel management of the RUFIC fueled CANDU-6 reactor. However, the transition RUFIC core simulations indicated that the 4-bundle shift refuelling scheme leads to some difficulties for the liquid zone control system. Therefore, an optimizing scheme for the transition core fuel management is being investigated by using 2- and 4-bundle shift schemes.