Abstract
This paper presents a study on the process engineering aspects of relevance to the industrial implementation of ThO2 and (Th, U)O2 mixed oxide (MOX) pellet type fuel manufacturing. The paper in particular focuses on the recycling of thoria based fuel production scrap which is an economically important component in the fuel manufacturing process. The thoria based fuels are envisaged for Advanced Heavy Water Reactor (AHWR) and other reactors important to the Indian Nuclear Power Programme. A process was developed for recycling the chemically clean, off-specification and defective sintered ThO2 and (Th, U)O2 MOX nuclear fuel pellets. ThO2 doesn’t undergo oxidation or reduction and thus, more traditional methods of recycling are impractical. The integrated process was developed by combining three basic approaches of recycling namely mechanical micronisation, air oxidation (for MOX) and microwave dissolution-denitration. A thorough investigation of the influence of several variables as heating method, UO2 content, fluoride and polyvinyl alcohol (PVA) addition during microwave dissolution-denitration was recorded on the product characteristics. The suitability evaluation of the recycled powder for re-fabrication of the fuel was carried out by analyzing the particle size, BET specific surface area, phase using XRD, bulk density and impurities. The physical and chemical properties of recycled powder obtained from the sintered (Th1-y, Uy)O2 (y; 0 - 30 wt%) pellets advocate 100% utilisation for fuel re-fabrication. Recycled ThO2 by integrated process showed distinctly high sinterability compared to standard powder evaluated in terms of surface area and particle size.
Highlights
The recycling of valuable materials is important for the nuclear industry like other industrial processes
This paper presents a study on the process engineering aspects of relevance to the industrial implementation of ThO2 and (Th, U)O2 mixed oxide (MOX) pellet type fuel manufacturing
The specific surface area and particle size were found to be poor, which may not be sintered to the densities required for an oxide fuel typically > 90% of theoretical density (TD)
Summary
The recycling of valuable materials is important for the nuclear industry like other industrial processes. The recycling comprises recovery of rejected nuclear fuel materials and their utilization for re-fabrication of the fuel. Thorium dioxide or thoria (ThO2) has gained more interest considering its resources and long-lived waste concerns It is more abundant in the earth crust and the thorium fuel cycle generates lesser minor actinides than its uranium analogue. The third stage of power programme is built on ThO2 based MOX fuels keeping in mind the long term deployment of thorium based reactors for sustainable energy [3] [4]. In this direction, AHWR is being set-up as technology demonstration reactor [4]. The proposed fuel is Th-LEU MOX having UO2 composition from 18 to 22.5 wt% for AHWR-LEU [5]
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