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A comparative study was performed with different designs of the fast breeder reactor (FBR) blanket to evaluate the performance of plutonium breeding accompanied with denaturing, and trans-uranium (TRU) transmutation for enhancement of the proliferation resistance and actinide management in the future fuel cycle. Four designs of the FBR blanket fuel were intercompared, conventional depleted uranium (DU) oxide fuels, DU with TRU oxide fuels, DU with TRU oxide fuels with homogeneous/heterogeneous moderators. As results, with heterogeneous moderator in the axial and the radial blanket fuels, the greatest TRU transmutation and plutonium denaturing performance were attained without deteriorating fuel breeding. Design optimization was performed as for ZrH 1.65 moderator rod/pellet arrangement in the axial and the radial blanket fuel assemblies. The optimum number of moderator rods per assembly was 25 (11% of the number of total rods) with proper mutual interval (2–3 cm) and symmetrical arrangement in the radial blanket, and insertion of 1 cm thick ZrH 1.65 moderator pellets to 4 and 10 cm from the top and the bottom planes of the active core was the optimum design in the axial blanket, in order to achieve the highest TRU transmutation ratio and plutonium denaturing performance without deteriorating fuel breeding. From the non-proliferation aspect, material attractiveness of plutonium were evaluated comparing with the criterion based on decay heat, and required TRU doping ratio in DU with TRU oxide fuel were proved to be as 1.6–2.5 wt.% with heterogeneous moderator, 2.1–3.0 wt.% with homogeneous moderator, and 4.1–5.0 wt.% without moderator. The heterogeneous loading of moderation showed the great advantages in fuel treatment in clear the heat generation limit criterion, as well as mass requirement to the initial and multi-cycle phase.

The design consideration of depleted U and Am (DU-Am) oxide fuel pin was performed for Pu denaturing in the framework of the protected plutonium production based on the irradiation analyses of the DU samples irradiated in the environment of broad range of neutron energy in the experimental fast reactor Joyo. From the results of irradiation analyses of DU, it was confirmed that there is a strong dependence of transmutation behavior of DU on the ratio of neutron flux in the resonance region to the total neutron flux, namely resonance neutron ratio, even in a fast reactor. Also, it was confirmed that there is a strong effect of sample material form and shape on generated Pu nuclide inventory especially near the reflector area (>20% resonance neutron ratio), because of the intensive self-shielding of 238 U, though less is expected for 241 Am. Sensitivity study of hypothetical DU-Am oxide fuel pellet irradiation on neutron energy and burn-up was performed to evaluate significant gradient of radial 238 Pu isotopic composition profile (e.g., from 12% to 18% distribution in 3% Am doping, in 30% resonance neutron ratio and in the neutron fluence of 4.0 × 10 22 n/cm 2 inside a large pellet with softened neutron spectrum), and vulnerability of the fuel pellet surface in terms of Pu denaturing was revealed. Design consideration of radial zoning of 241 Am content was introduced to flatten the radial distribution of isotopic composition of Pu. The results of radial zoning of 241 Am (4% and 3% Am in the outer and inner zone of DU-Am oxide fuel pellet) in hypothetical irradiation neutronics analysis showed the radial profile of produced Pu is over 15 at.% of 238 Pu isotopic composition in any zone and meets the criterion of Kimura et al. based on decay heat of Pu to impede utilization to fission explosive devices.

The proliferation resistance of plutonium can be enhanced by isotopic denaturing and one of the features of Pu isotopic denaturing is increasing of the spontaneous fission neutron emission rate. A high spontaneous fission neutron emission rate causes “predetonation” in a nuclear explosive device, and it makes the designing and building of a nuclear explosive device more complicated. In this paper, the enhancement of Pu proliferation resistance by isotopic denaturing was evaluated based on spontaneous fission neutron emission rate using a simple nuclear explosive device model. The feature of spontaneous fission neutron was evaluated with probabilistic approach, and a new Pu categorization which makes enable to categorize plutonium by its isotopic compositions was proposed based on the evaluation results. The Pu categorization was applied to an evaluation of the proliferation resistance of plutonium produced in LWRs and FBRs using the evaluation function, “Attractiveness” for two types of plutonium; plutonium produced in typical LWRs and FBRs, and denatured plutonium produced by transmutation of MAs.

The practical feasibility of 126Sn transmutation in spallation targets of accelerator-driven systems was evaluated from the viewpoints of accumulation of radioactive spallation products and neutron production as well as transmutation amount of 126Sn. A cylindrical liquid 126Sn target whose length depends on proton beam energy was described, based on a Pb-Bi target design of accelerator-driven system being developed in JAEA. A proton beam of 1.5 GeV-20mA was estimated to give the transmutation rate of 126Sn 6.4 kg/yr, which corresponds to the amount of 126Sn annually discharged in 27 LWRs of 1GWt and 33 GWd/THM. The equilibrium radioactivity of spallation products would reach 9% of that of 126Sn transmuted in the spallation target, and the equilibrium toxicity would be just 3%. Some parametric analyses showed that the effective half-life of 126Sn could be reduced through a proper reduction of the target size. The 126Sn target was calculated to produce 40 neutrons per proton of 1.5 GeV and give a neutron sp...

Currently, two systems for TRU (transuranics) transmutation, the critical and the subcritical reactor systems, are being investigated by many research groups. Both systems have their own advantages and disadvantages. In this study, the comparative analyses of nuclear characteristics between both systems were performed. The fuel loaded into a TRU transmutation reactor includes few fertile nuclides, which contribute to stability and safety of the nuclear reactor. Thus, this study was focused on the intrinsic difference in the dynamic parameters between both systems. At the same time, the neutronic effects of the external source and the neutron absorber on the nuclear characteristics were also analyzed for the subcritical and the critical systems, respectively. Neutron flux spectrum, fuel temperature coefficient, coolant temperature coefficient, delayed neutron fraction, and neutron generation time were considered for comparative analyses. Based on the obtained results, some conclusions and proposals...

A subcritical reactor for TRU (Transuranics) transmutation, HYPER (HYbrid Power Extraction Reactor), is under development at KAERI (Korea Atomic Energy Research Institute). For the HYPER system, a pyrochemical process is being considered for fuel reprocessing, due to its own characteristics of nuclear proliferation resistance. Separated from the partitioning process, the fuel contains not only TRU but also the considerable percentages of impurities such as uranium and lanthanides. In our previous studies, the eigen mode calculation had been performed without the external source effects, for the purpose of analyzing the fuel composition effects on the HYPER core characteristics. And the results had shown that the dynamic behavior of the HYPER system becomes unstable as the amount of impurities increases. In this paper, the external source neutron effects on the core characteristics sensitivity to the fuel composition were investigated. Assuming various recovery factors of uranium and lanthanides, some dyna...