Finally, the increased concentrations of TRU nuclides in the fuel cycle would complicate the fuel handling, reprocessing, and fabrication due to increase levels of radiation. Some of the higher MA nuclides mentioned above in particular Cm244, Cm246, Cm248, and Cf252 have relatively high branching ratio to spontaneous fission (SF). The neutrons released in SF process are very hard to shield so that accumulation of SF neutrons emitting nuclides would aggravate the TRU containing fuel handling and fabrication problem. Additionally, the TRU separation based on the aqueous reprocessing techniques may not be suitable for the reprocessing of fuels with high TRU concentrations. The organic solvents used for separation of TRU from the fission products degrade rapidly when exposed to high radiation or elevated temperatures caused by the decay of TRU. As a result, non-aqueous separation techniques based on pyrochemical or pyrometallurgical reprocessing may be required.
1.5. Thesis Organization This thesis consists of ten chapters. The first chapter briefly introduced the problematic issues associated with once-through fuel cycle such as accumulation of long lived radioactive waste, proliferation resistance, and poor utilization of natural resources. Then, short overview of the suggested in the past solutions and strategies was presented. The possibility of addressing the most important once through fuel cycle issues using exclusively the existing LWRs was proposed and justified. The list of potential associated technical challenges was subsequently presented. The evaluation of neutronic performance of the two most promising cycles, with respect to the TRU destruction capabilities, fuel matrix candidates is presented in Chapters 2 and 3 focusing on thorium oxide and fertile free fuel matrices respectively. TRU destruction rates and TRU residual fractions in the spent fuel are the main parameters of interest in the discussion. The reactivity feedback coefficients and soluble boron reactivity worth are also reported as primary indicators of practical fuel design feasibility. Chapter 4 compares the evaluated thorium oxide and fertile free fuel options in terms of their repository performance characteristics in a once through burndown scenario aiming at the reduction of existing TRU stockpile and at constraining future TRU generation. The performance
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