S. Şahin, K. Yıldız, H. M. Şahin, A. Acır, N. Şahin, T. Altınok
March 26, 2013
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Nuclear waste actinides can be used as a booster fissile fuel material in form of mixed fuel with thorium in a CANDU reactor in order to assure the initial criticality at startup. Two different fuel compositions have been found useful to provide sufficient reactor criticality over a long operation period: 1) 95% thoria (ThO 2 )+5% minor actinides MAO 2 and 2) 90% ThO 2 +5% MAO 2 +5% UO 2 . The latter allows a higher degree of nuclear safeguarding through denaturing the new 233 U fuel with 238 U. 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 10 years. The criticality starts by k ∞ >1.3 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout in the actinide fuel. The criticality becomes quasi constant after the 2 nd year and remains close to k ∞ = ∼1.06 for ∼10 years. After the 2 nd 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 200000 MW.D/MT), provided that the fuel rod claddings would be replaced periodically (after every 50000 or 100000 MW.D/MT). The reactor criticality can be maintained 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.