S. Şahin, A. Acır, H. M. Şahin
April 25, 2013
Criticality and burn up behavior of the Fixed Bed Nuclear Reactor (FBNR) are investigated for the mixed fuel 233 UO 2 /ThO 2 as an alternative to low enriched 235 UO 2 fuel. CERMET fuel with a zirconium matrix and cladding has been used throughout the study. The main results of the study can be summarized as follows: Reactor criticality is already achieved by ∼2% 233 UO 2 with the mixed 233 UO 2 /ThO 2 fuel. At higher 233 U fractions, reactor criticality rises rapidly and exceeds k eff > 1.5 already by 9% 233 UO 2 . With 100% 233 UO 2 , start up criticality can reach k eff = 2.0975. Time dependent reactor criticality k eff and fuel burn up have been investigated for two different mixed fuel 233 UO 2 /ThO 2 compositions, namely: 4% 233 UO 2 + 96% ThO 2 for a reactor power of 40 MW el (120 MW th ) and 9% 233 UO 2 + 91% ThO 2 for a reactor power of 70 MW el (210 MW th ). Sufficient reactor criticality (k eff > 1.06) for continuous operation without fuel change can be sustained during ∼5 and 12 years with 4% and 9% 233 UO 2 fractions in the mixed fuel, leading to burn ups of ∼36000 and >105000MWD/t, respectively. Thorium based fuel produces no prolific uranium. Plutonium production remains negligible.