A feasibility study on CANFLEX-RU 4-BUNDLE shift scheme in CANDU-6 reactor

A feasibility of the 4 RUFIC (Recovered Uranium Fuel in CANDU) fuel bundle shift refuelling scheme for a CANDU-6 core was evaluated through the transition core simulation by changing from the existing 37-element natural uranium (NU) fuel to the 0.92 w/o RUFIC fuel and the 1200 full power day (FPD) equilibrium core simulation, where the CANFLEX-RU fuel is called as RUFIC. The computer code system used in this work is WIMS-AECL/DRAGON/RFSP. The results of transition and equilibrium core fuelling simulations show that the variations of maximum channel power (MCP) and maximum bundle power (MBP) as a function of FPDs were maintained within the self-imposed operating limits which are currently employed in Wolsong reactors. The maximum channel power peaking factor (CPPF) is maintained below 1.14 in all FPDs, which is set as the minimal margin of 8 % for the refuelling in a Wolsong unit. Concerning the operating limits on the MCP, MBP, and CPPF, a 4-bundle shift refuelling scheme is feasible to refuel the RUFIC fuel bundles into an operating CANDU-6 reactor. Also, data on element power and element power-increase upon fuelling as a function of burnup were extracted and compiled for fuel performance assessment. It is shown that all the fuel element powers are below the SCC threshold curve for normal operation and for power-increase, except that the power boost for some of the ring-4 (outermost ring) elements is above the SCC threshold. Considering the fact that fuel defects occur when both the results on the two envelops violate the SCC threshold curve simultaneously, no defect of RUFIC fuel bundles is expected in the 4-bundle shift refuelling scheme. And, it is revealed that there would be some improvement in the critical channel power (CCP) in a channel with the RUFIC fuel bundle. (author)