Masatoshi Kawashima

Safety features of self-consistent nuclear energy system

Abstract The basic condition and concept to eliminate recriticality-related problems has been investigated from the viewpoint of the safety features of the SCNES. The passive shutdown capability of the intact core was achieved by self-controllability due to the flat core geometry of high thermal conductivity fuel. Recriticality during severe transients was found to be eliminated by the self-terminability due to the controlled material relocation of the leading channel, where the incoherent and localized fuel motion was generated in the degraded core.

Long-life water cooled small reactor with U-Np-Pu fuel

The paper presents the advanced concept of a long-life small light water reactor in which the fuel irradiation time is comparable with reactor life-time. The equilibrium analysis reveals that the U-Np-Pu fuel with unique neutronic properties allows to keep sufficient criticality up to burnup value about 140GWd/tHM. The fuel recycle does not lead to additional Pu accumulation. Both Pu and Np are well protected against un-controlled proliferation by a large fraction of 238Pu in their mixture. To improve the reactor safety, the wider fuel pin lattice was applied. The radiation damage of structural materials is within the stainless steel limitation.

Safety characteristics of the SCNES core

Abstract The core concept of the Self-Consistent Nuclear Energy System (SCNES) and its safety characteristics have been investigated from the view point of the elimination of recriticality. The recriticality potential can be eliminated based on characteristics of self-controllability to prevent the core damage and self-terminability to limit the propagation of core disruption. These two characteristics are simultaneously achieved by the radial heterogeneous two region core with different height. This core consists of leading and driver zones where hybrid metallic fuels with different melting point are installed. The self-controllability can be achieved by decreased coolant density effect due to the above core sodium plenum at the leading zone. The self-terminability is achieved by the Controlled Material Relocation (CMR), which is essentially the preceding downward in-pin fuel relocation selectively generated at the leading zone. U-Pu-1Zr alloy is used to the leading zone fuel due to lower melting point (900°C) than the driver fuel of U-Pu-10Zr(1100°C). Based on the quantitative investigations, it was emphasized that the recriticality potential can be eliminated by the in-pin fuel CMR even for severe unscrammed events such as a total pump stick for the primary coolant system and a total control rods withdrawal.

Long-lived FP burning based on the actinide recycle metal fuel core

Abstract Feasibility of burning of the major long-lived FPs (I, Pd, Tc, Sn, Se, Zr, Cs) while maintaining fuel breeding capability for the Self-Consistent Nuclear Energy System is evaluated based on the actinide recycle metal fuel core of a fast reactor. It is shown that I, Pd, Tc, Sn, Se, and Zr can be burnt simultaneously by an aid of the isotope separation of Pd-107, Zr-93 and Se-79. Cs, which is difficult to burn with the other FPs, should be utilized as an in-reactor shielding material to confine in the system. The selection of the target FPs to be burnt are also validated by using the Burden Index. The overall assessment based on those results indicates that the developed system has the great potential to achieve the goal of the Self-Consistent Nuclear Energy System.

Development of the core-bowing reactivity analysis code system ATLAS and its application to a large FBR core

A new code system called ATLAS has been developed to calculate core-bowing reactivity feedback behavior in fast breeder reactor cores. Based on the structural mechanics of a core (core mechanics), the code also incorporates neutron physics and thermo-hydraulic calculations. Using this new code system, the core barrel restraint system of a typical large fast breeder reactor was investigated in detail and core-bowing reactivity coefficients were determined to assess their sensitivity to several design parameters.

An application of metal fuel cycle technology toward self-consistent nuclear energy system (SCNES) concept

A fast reactor core and fuel cycle concept has been discussed for Self-Consistent Nuclear Energy System (SCNES) concept. This paper discussed loading material candidates for long-lived fission products (LLFPs) and LLFPs burning capability. Some of LLFPs were possible to be loaded in metal of the generated form. The potential for LLFP-confinement in the reactor system is discussed along with metallic fuel cycle concept. The proposed fuel cycle scheme is a successful candidate for SCNES concept.

Neutronic feasibility of an LMFBR super long-life core (SLLC)

Abstract The LMFBR Super Long-Life Core (SLLC) concept has evolved over the last few years as one of the targets of innovative approaches for future FBR cost reduction. An idea for SLLC has been developed wherein the core lifetime is extended up to the plant life of about 30 years by applying the radially and axially multi-zoned core concept (the improved homogeneous core concept). The main purpose of the present study is placed on the evaluation of neutronic feasibility of the 1000 MWe class SLLC concept. The core size of the present SLLC, which is approximately 3 to 4 times as large as those of the current 1000 MWe core design, was determined by the limit of the maximum fast neutron fluence level, which was tentatively assumed to be 5–6 × 10 23 nvt as the target of the future development of advanced cladding materials. Emphasis is placed on the discussion of neutronic performances of cores with oxide fuels rather than metal or carbide fuels. The present study has shown that proper zoning of the different plutonium enrichment fuels at the initial core makes it possible to achieve small enough reactivity loss during 30-year burnup while satisfying mild variation of the subassembly power distributions using a higher fuel volume fraction of about 50%. Effects of important neutronic parameters on the core performances are also discussed.

Physics Benchmark Experiments and Analysis for Reflector-Control-Type Small Fast Reactors at TOSHIBA Nuclear Critical Assembly

New physics benchmark experiments were successfully accomplished in order to study the basic characteristics of a reflector controlled small reactor 4S and to validate core design methods using Toshiba NCA critical facility. The experience gained through the analyses provides rationality of nuclear design methodology and nuclear library. Continuous Monte Carlo transport calculation method using JENDL3.2 enables core designers to predict reflector control characteristics with high reliability. Prediction accuracy for burn-up characteristics is needed for further design activity.

A feasibility study on FP incineration for Self-Consistent Nuclear Energy System (SCNES)

Abstract A fast reactor core and fuel cycle concept is discussed for the future “Self-Consistent Nuclear Energy System (SCNES)” concept. The present study mainly discussed long-lived fission products (LLFPs) burning capability and recycle scheme in the framework of metal fuel fast reactor cycle, aiming at the goals for fuel breeding capability and confinement for TRU and radio-active FPs within the system. Combining neutron spectrum-shift for target sub-assemblies and isotope separation using tunable laser, LLFP burning capability is enhanced. This result indicates that major LLFPs can be treated in the additional recycle schemes to avoid LLFP accumulation along with energy production. In total, the proposed fuel cycle is a candidate for realizing SCNES concept.

Development of Uranium-Free TRU Metallic Fuel Fast Reactor Core

A TRU-burning fast reactor cycle associated with a uranium-free trans-uranium (TRU) metallic fuel core is one of the solutions for radioactive waste management issue. Use of TRU metallic fuel without uranium makes it possible to maximize the TRU transmutation rate in comparison with uranium and plutonium mixed-oxide fuel because it prevents the fuel itself from producing new plutonium and minor actinides, and furthermore because metallic fuel has much smaller capture-to-fission ratios of TRU than those of mixed-oxide fuel. Also, adoption of metallic fuel enables recycling system to be less challenging, even for uranium-free fuel, because a conventional scheme of fuel recycling by electrorefining and injection casting is applicable.