Hiroshi Sagara

Protected Plutonium Breeding by Transmutation of Minor Actinides in Fast Breeder Reactor

The improvement of proliferation resistance properties of Pu and the burnup characteristics of fast breeder reactor (FBR) had been studied by utilizing minor actinides (MAs) to produce more 238Pu from 237Np and 241Am through neutron capture reaction. The higher the 238Pu content in the fuel, the higher the proliferation resistance of the fuel would be owing to the natural characteristics of 238Pu with high decay heat and high neutron production. The present paper deals with the assessment of passive measure against nuclear material proliferation by focusing on improving the inherent proliferation barrier of discharged Pu from an FBR. Results showed that 5% MA doping to the blanket of an FBR gives as high as 17–19% 238Pu, which could be seen as a significant improvement of the proliferation properties of Pu. Moreover, additional 5% ZrH2, togather with 5% MA doping to the blanket, could enhance the 238Pu fraction much more (22–24%). With an assumption of protected Pu whose 238Pu isotopic fraction is more than 12%, the present paper revealed that protected Pu could be produced more than the Pu consumed (protected Pu breeding) through incineration in an FBR with doping of a minimum 3% MAs or (2% MAs + 5% ZrH2) to the blanket.

Denaturing of Plutonium by Transmutation of Minor-Actinides for Enhancement of Proliferation Resistance

Feasibility study for the plutonium denaturing by utilizing minor-actinide transmutation in light water reactors has been performed. And the intrinsic feature of proliferation resistance of plutonium has been discussed based on IAEAs publication and Kesslers proposal. The analytical results show that not only 238Pu but also other plutonium isotopes with even-mass-number have very important role for denaturing of plutonium due to their relatively large critical mass and noticeably high spontaneous fission neutron generation. With the changes of the minor-actinide doping ratio in U—Pu mix oxide fuel and moderator to fuel ratio, it is found that the reactor-grade plutonium from conventional light water reactors can be denatured to satisfy the proliferation resistance criterion based on the Kesslers proposal but not to be sufficient for the criterion based on IAEAs publication. It has been also confirmed that all the safety coefficients take negative value throughout the irradiation.

Evaluation of Proliferation Resistance of Plutonium Based on Decay Heat

The present paper is prepared for the peaceful use of nuclear energy. Proliferation resistance of plutonium can be enhanced by increasing the decay heat of plutonium. For example, it can be enhanced by increasing the isotopic fraction of 238Pu, which has the largest decay heat among plutonium isotopes. In the present paper, the proliferation resistance of plutonium was evaluated based on decay heat with a physical assessment model. New criteria were proposed to evaluate the proliferation resistance based on isotopic compositions of plutonium from the viewpoint of decay heat. The present criteria were applied to evaluate the proliferation resistance of plutonium produced in typical Light Water Reactor and Fast Breeder Reactor based on an evaluation function “Attractiveness” as case studies.

Transmutation of long-lived fission products driven by D-T and D-D fusion: Specific neutronics and radiological consequences

In view of the poor transmutation environments in fission reactors, elimination of long-lived fission products (FPs) remains an unresolved problem in the quest for a harmonized nuclear energy system. Since plasma fusion technology could provide effective neutron support, it is important to elaborate the qualities, features, and dimensions of a fusion neutron source exclusively oriented to FP transmutation, and this forms the main objective of this paper. Recent trends in fusion technology are examined to shape the conceptual blanket design features for D-T- and D-D-driven transmuters that match the demanding set of transmutation requirements. Material behavior under neutron irradiation in these blankets constitutes the central issue underlying this paper and yields the operational limits and radiological cost of FP incineration.

Protected Plutonium Production by Transmutation of Minor Actinides for Peace and Sustainable Prosperity—Irradiation Tests of Np and Np-U Samples in the Experimental Fast Reactor JOYO (JAEA) and the Advanced Test Reactor at INL—

A project on Protected Plutonium Production (P3) was proposed by Tokyo Institute of Technology as part of a nonproliferation research program for plutonium (Pu) utilization in nuclear reactors. The project is aimed at the production of inherently protected Pu by the addition of 237Np to uranium (U) fuel. In order to validate this P3 concept, two irradiation tests were performed. In the first, a determination of Pu isotopes in 237Np samples irradiated in the experimental fast reactor JOYO was done to evaluate 238Pu production from 237Np under fast neutron spectra. The fast reactor can undertake P3, which can be better performed in the reflector region. In the test, the percentage of the total amount of 238Pu atoms transmuted from 237Np atoms by irradiation was around 90%. In the second test, 2, 5, and 10% Np-containing U samples were irradiated in the Advanced Test Reactor at the Idaho National Laboratory (INL) to evaluate 238Pu production in the thermal neutron region. The fuel specimens were removed from the core at 100, 200, and 300 effective full power days (EFPDs), and then a postirradiation examination was completed at an analytical laboratory in the Materials & Fuels Complex (MFC) at the INL. For the samples after irradiation for 300 EFPDs, Np depletions were about 60% for 2% neptunium (Np)-U samples and about 50% for 5 and 10% Np-U samples. The 238Pu-to-Pu ratios were about 20, 30, and 45% for 2, 5, and 10% Np-U samples, respectively.

Inherent Protection of Plutonium by Doping Minor Actinide in Thermal Neutron Spectra

The present study focuses on the exploration of the effect of minor actinide (MA) addition into uranium oxide fuels of different enrichment (5% 235U and 20% 235U) as ways of increasing fraction of even-mass-number plutonium isotopes. Among plutonium isotopes, 238Pu, 240Pu and 242Pu have the characteristics of relatively high decay heat and spontaneous fission neutron rate that can improve proliferation-resistant properties of a plutonium composition. Two doping options were proposed, i.e. doping of all MA elements (Np, Am and Cm) and doping of only Np to observe their effect on plutonium proliferation-resistant properties. Pressurized water reactor geometry has been chosen for fuels irradiation environment where irradiation has been extended beyond critical to explore the subcritical system potential. Results indicate that a large amount of MA doping within subcritical operation highly improves the proliferation-resistant properties of the plutonium with high total plutonium production. Doping of 1% MA or Np into 5% 235U enriched uranium fuel appears possible for critical operation of the current commercial light water reactor with reasonable improvement in the plutonium proliferation-resistant properties.

Radiation Dose as a Barrier against Proliferation for Advanced Fuel Compositions

The paper deals with the analysis of radiation barriers against proliferation focusing on denatured plutonium compositions and associated with the process of plutonium denaturing by some other heavy metals. The issue is discussed from the viewpoint of radiation dose induced by both gamma and neutron radiation, thus reflecting the technical and human resources the potential proliferators should have to meet the challenge of making a nuclear explosive.

Denaturing Generated Pu in Fast Breeder Reactor Blanket

Protected Pu production (P3) is a recently developed concept to enhance the proliferation resistance properties of Pu by increasing the fraction of even-mass-number Pu isotopes thus leading to the denaturing of Pu. The present paper deals with the possibility of denaturing Pu by consideration of Pu and minor actinides (MAs) multicycling in medium-size fast breeder reactors (FBRs). It was found that multicycling of Pu and MAs in FBRs enhances the proliferation resistance of Pu by increasing the fraction of evenmass-number Pu isotopes. The proliferation resistance of Pu in P3 recycling options satisfied criteria based on Kesslers proposal, i.e., 6% 238Pu content, and Pellauds proposal, i.e., 30% 240Pu content. The normalized attractiveness of Pu in P3 recycling options satisfied both criteria in the core as well as in the blanket with the combination of even-mass-number Pu isotopes. At the initial introduction, two P3 FBRs (714 MWth class) with the addition of 5 wt% MA into the blanket can be operated using the annual discharged spent fuel in Japan.

Numerical analysis of irradiated Am samples in experimental fast reactor Joyo

Americium is a key element to design the FBR based nuclear fuel cycle, because of its long-term high radiological toxicity as well as a resource of even-mass-number plutonium by its transmutation in reactors, which contributes the enhancement of proliferation resistance. The present paper deals with the numerical analysis of the Am sample irradiation in Joyo to examine the transmutation performance of pure isotope in fast neutron environment during the irradiation, and deals with the comparison with the experimental result to evaluate the accuracy of current available numerical tool. In 241Am pure isotope sample, the burn-up calculation of Am transmutation ratio and principal nuclides accumulation are agreed with the measured data within 1-σ uncertainty caused of cross-section covariance. Isomeric ratio of 242Am in total 241Am capture reaction were calculated as 0.852±0.016 in the core and 0.85±0.025 in the axial and radial reactors. The current data and recently reported data by Koyama et. al 2008 support the latest version of nuclear data sets in ENDFB-VII and JENDL/AC-2008. From the view point of proliferation resistance, it was confirmed 241Amp reduces un-attractive Pu to abuse from the beginning to the end of irradiation, and it would have important role to denature Pu in future FBR based nuclear fuel cycle.

Feasibility of Reprocessed Uranium in LWR Fuel Cycle for Protected Plutonium Production

Protected plutonium production (PPP) is an intrinsic measure to enhance the proliferation resistance of Pu by raising the 238Pu isotopic concentration, which denatures Pu on account of the high spontaneous fission neutron (SFN) rate and large decay heat (DH). This study is aimed at examining the feasibility of reprocessed uranium (RepU) with or without the addition of minor actinide (MA) in LWR fuel cycle for PPP and to make a tentative economic assessment of RepU possessing the PPP feature. It was analytically clarified that RepU enriched to 5% 235U by centrifugation produced denatured Pu at higher burnup than about 40GWd/t. By the addition of more than 0.5% MA to RepU and natural uranium both enriched to 5%, Pu generated in the uranium fuel with MA added could be denatured up to 40 GWd/t at least. A diagram designed with functions of SFN rate and DH explicated the PPP features of re-enriched RepU and enriched natural uranium with or without MA addition. The economic assessment indicated that the cost of fuel cycle applying re-enriched RepU would be comparable to that of the conventional fuel cycle, if the cost of the source RepU is low. In addition, the LWR fuel cycle applying RepU for PPP was discussed.