Increased fuel burn up in a CANDU thorium reactor using weapon grade plutonium

Abstract

Weapon grade plutonium is used as a booster fissile fuel material in the form of mixed ThO2/PuO2 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Two different fuel compositions have been used: (1) 97% thoria (ThO2) + 3%PuO2 and (2) 92% ThO2 + 5% UO2 + 3% PuO2. The latter is used to denaturize the new 233U fuel with 238U. The temporal variation of the criticality k? and the burn-up values of the reactor have been calculated by full power operation for a period of 20 years. The criticality starts by k? = ~1.48 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout. The criticality becomes quasi constant after the second year and remains above k? > 1.06 for ~20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burn up could be achieved with the same fuel material (up to 500,000 MW·D/T), provided that the fuel rod claddings would be replaced periodically (after every 50,000 or 100,000 MW·D/T). The reactor criticality will be sufficient until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.