Performance analysis of 233U for fixed bed nuclear reactors

Criticality and burn up behavior of the Fixed Bed Nuclear Reactor (FBNR) are investigated for the mixed fuel UO /ThO as an alternative to low enriched UO 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% UO with the mixed UO /ThO fuel. At higher U fractions, reactor criticality rises rapidly and exceeds k > 1.5 already by 9% UO . With 100% UO , start up criticality can reach k = 2.0975. Time dependent reactor criticality k and fuel burn up have been investigated for two different mixed fuel UO /ThO compositions, namely: 4% UO + 96% ThO for a reactor power of 40 MW (120 MW ) and 9% UO + 91% ThO for a reactor power of 70 MW (210 MW ). Sufficient reactor criticality (k > 1.06) for continuous operation without fuel change can be sustained during ∼5 and 12 years with 4% and 9% UO 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.