Back end of Indian nuclear fuel cycle-A road to sustainability

Abstract

Indian policy of ‘closed fuel cycle’ implies reprocessing of the spent fuel thereby recycling the uranium and plutonium extracted from the spent fuel. Reprocessing leads to the generation of intermediate and high-level liquid wastes containing various radionuclides that need to be contained for periods ranging from few years to thousands of years. Low & intermediate level non-alpha solid and solidified wastes generated during reactor operation are disposed in near surface disposal facilities which are monitored regularly during and after operations. The normal gaseous and liquid wastes are discharged in air/water bodies after appropriate treatment and dilution and complying with regulatory norms of Indian Atomic Energy Regulatory Board, Mumbai.The intermediate level wastes from reprocessing are first treated with basic objective of achieving volume reduction. Indigenously developed sorbents and solvents have been deployed. These have resulted in higher volume reductions with desirable decontamination factors as against their direct immobilization in bitumen and organic polymers. For high-level waste, a three-step strategy involving immobilization, interim retrievable storage and ultimate disposal in geological formations is followed. In the Indian context, the future policy for the management of high-level liquid waste is to separate (partition) minor actinides and burn them in fast reactors and/or accelerator driven subcritical systems. The high level waste also contains useful isotopes like 137Cs, 90Sr, etc. which can be deployed for societal benefits. The technologies have been developed to separate these minor actinides, fission products like 137Cs, 90Sr and are discussed in the paper.For immobilization (vitrification) of the waste ‘Sodium borosilicate glass’ composition is deployed. Vitrification facilities on Industrial scale are in operation at Tarapur and Kalpakkam. To take care of the decay heat in the vitrified products, the waste is stored in intermediate storage for about thirty o forty years. The storage vault for interim storage has been designed, constructed and is operational at Tarapur and similar higher capacity facility is under construction at Kalpakam. A solvent extraction based plant for the recovery of 137Cs has been operated and radio cesium recovered has been converted into vitrified irradiation pencils. Vitrified high-level waste volumes currently generated and stored are not sufficient to call for setting up of a Geological Disposal Facility (GDF) immediately. Based on the projected growth in nuclear power profile for India (∼54 GWe by year 2032), vitrified waste cumulatively produced and interimly stored for cooling till 2075, would only thereafter call for their economic transfer to GDF for the final disposal in a phased manner. In this paper, the technological and innovative details of the above aspects are presented.