Proposed alternative fuel cluster for Indian PHWRs

Full text: Presently 12 PHWRs of 220 MWe and 2 PHWRs of 540 MWe are in operation. 3 new PHWRs of 220 MWe are expected to get commissioned soon and some old units will also require fresh core loading after enmass coolant channel replacement (EMCCR).Hence there is a growing demand for Natural Uranium against the limited supply of raw material. Thus to meet its fuel requirement and to conserve natural uranium, NPCIL is exploring various options. This paper aims to propose two such possible fuel clusters which have been studied specially keeping in mind the requirement of fresh core loading. Main emphasis is given to available materials viz. reprocessed Plutonium from 220 MWe PHWRs which can be mixed with Deeply Depleted Uranium (DDU) or Thorium. The safety requirements like worth of Shut down and regulating devices, various reactivity coefficients etc. are evaluated and found to be satisfactory. It has been ensured that the existing 220 MWe PHWR core hard ware requirements are not disturbed. The concentration of Plutonium for MOX with DDU is worked out to have general characteristics more or less equivalent to Natural Uranium bundle while that for the MOX with Thorium is worked out to achieve relatively higher discharge bum up to get effective utilization of thorium