Feasibility study of large MOX fueled FBR core aimed at the Self-Consistent Nuclear Energy System

The potential of a MOX fueled fast breeder reactor (FBR) is evaluated with regard to its ability to transmute radioactive nuclides and its safety when incorporated in the so-called self-consistent nuclear energy system (SCNES). The FBR's annual production amounts of selected long-lived fission products (LLFPs), Se-79, Tc-99 Pd-107, I-129, Cs-135 and Sm-151, can be transmuted by using a radial blanket region and a part of a lower axial blanket region without any significant impact on its nuclear and safety characteristics. The other LLFPs are confined in the system. The hazard index level of the LLFPs per one ton of spent fuel from the system after 1000 years is as small as that of a typical uranium ore. To realize self-controllability (passive safety), the proposed FBR core concept employs gas expansion modules and sodium plenum above the core. To realize self-terminability, even if MOX fuel melting should cause a core compaction, recriticality of the core can be avoided by a fuel dilution and relocation module. The results show the MOX fueled FBR core has potential applicability to the SCNES. With the final goal of the ideal SCNES, fundamental applicability of various coolants and fuels is evaluated based on neutron balance. It is shown that the harder the core spectra is, the larger the potential for transmuting LLFPs would be.     

Feasibility study on nitride fuel core and recycling system toward Self-Consistent Nuclear Energy System

The concept of a nuclear fuel recycle system with a nitride fueled FBR core has been investigated as a part of related studies towards the Self-Consistent Nuclear Energy System (SCNES). Nitride fuel has been given attention because of its relatively high fuel density and high thermal conductivity. To materialize the SCNES concept, it is important to adequately use the excess neutrons produced in the chain reaction. The high fuel density of the nitride fuel brings out more of the excess neutrons and has a higher potential to transmute the long-lived fission products (LLFP's). The high thermal conductivity, in addition, provides margin of fuel melting, and gives negative feedback due to the Doppler reactivity in unprotected loss of flow accidents. In this paper, we discuss good use of nitride fuel in the SCNES.     

A metal fuel fast reactor core for the Self-Consistent Nuclear Energy System

Feasibility of transmutation 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 transmuted simultaneously by an aid of the isotope separation of Pd-107, Zr-93, Sn-126 and Se-79. Cs, which is difficult to transmute with the other FPs, is planned to be utilized as an in-reactor shielding material to confine in the system The overall assessment based on those results indicates that the developed system has the great potential toward the Self-Consistent Nuclear Energy System.     

Elimination of recriticality potential for the Self-Consistent Nuclear Energy System

The ultimate safety goal of the Self-consistent Nuclear Energy System (SCNES) is to eliminate the recriticality-problem based on a simple safety logic. The principle of the elimination of the recriticality-problem is the Controlled Material Relocation (CMR) to establish the neutronic shutdown by removing the molten fuel to the out of core before a large scale pool formation which has potential of energetics driven by a super prompt criticality.

The CMR concept should be reliable without significant impact on the core neutronic performance. As the typical core concepts to enhance this CMR characteristic, several design options are under consideration. They are fuel assemblies with inner duct structure (FAIDUS), fuel assemblies with hollow fuel pins in the axial blanket region (ABLE) for MOX fueled cores, and fuel assemblies without fuel pin bundle structure in the lower axial blanket region (ELAB) for the metallic fueled core. Based on the core design study and accident analyses, these CMR-oriented concepts have been found feasible without significant degradation of the neutronic performance

In order to experimentally confirm the effectiveness of the CMR concept for the MOX fueled core, the EAGLE project has been started in 1998 by Japan Nuclear Cycle Development Institute (JNC) and The Japan Atomic Power Company (JAPC). The EAGLE project is the experimental program utilizing the out-of pile test facility and in-pile facility IGR of the National Nuclear Center of the Republic of Kazakhstan (NNC/RK).     

Multilateral Assessment of the Fast Reactor System as a Component of the Future Sustainable Nuclear Energy and Paths for the System Deployment

The paper reviews main findings of the Joint Assessment Study on a Nuclear Energy System (NES) based on a Closed Nuclear Fuel Cycle with Fast Reactors (CNFC-FRs) that was performed within the IAEA project INPRO.     

A comparative neutronic study of the standard HEU core and various potential LEU alternatives for a typical MNSR system

A comparative study has been performed for neutronic analysis of highly enriched in uranium (HEU) and potential low enriched in uranium (LEU) cores for the Pakistan Research Reactor-2 (PARR-2) taken as a typical miniature neutron source reactor (MNSR) system. The group constant generation has been carried out using transport theory code WIMS-D4 and a detailed five-group RZ-model has been used in the CITATION code for multigroup diffusion theory analysis. The neutronic analysis of the 90% HEU reference and potential LEU alternative: UO₂, U₃Si₂ and U9Mo, cores has been carried out yielding 11%, 20.7% and 14.25% enrichments with corresponding values of excess reactivity: 4.33, 4.30 and 4.07 mk. These results have been found in good agreement with recently reported Monte Carlo-based transport theory calculations. The diffusion theory-based calculated values of thermal flux profiles for axial as well as for radial directions have been found to agree well with the corresponding experimental measurements. The UO₂-based LEU core has been found having flux spectrum closest to the reference core while U9Mo core has significantly harder flux spectrum at irradiation site.     

A study on the local behaviour of steel-concrete interfaces at and around large openings in the PSC inner containment dome

A finite element (FEM) study has been made to know the overall structural behaviour of a PSC inner containment (IC) dome having large steam generator (SG) openings with emphasis on the local behaviour of the steel-concrete interfaces near SG openings, under initial prestress transfer. The primary thrust of the work has been in the objective of predicting the possibilities of separation at the steel-concrete interface zones adjacent to the embedded plates of the SG openings. For the FEM analysis, the interface zone has been modeled using gap elements, the properties of which are derived from the results of the past experiments conducted on steel plate-concrete interface specimens. Important observations have been made regarding dome deformation and the stresses with special emphasis on the local behaviour of steel-concrete interfaces at and around SG openings.     

Experimental study of the fracture kinetics of a tubular 16MnNiMo5 steel specimen under biaxial loading at 900 and 1000 °C. Application to the rupture of a vessel bottom head during a core meltdown accident in a pressurized water reactor

This study proposes an experimental analysis of the creep, crack initiation and crack propagation phases in a 16MnNiMo5 steel subjected to thermomechanical loading representing a core meltdown accident in a pressurized water reactor involving the transfer of a molten corium bath to the bottom head. The experimental setup enabled a biaxial mechanical loading (internal pressure + tension) to be applied to a tubular specimen at 900 and 1000 °C. In addition to the usual temperature, load, displacement and pressure measurements, the specimen was observed by two high-speed numerical cameras and an infrared camera. The crack's initiation and propagation conditions and the depressurization law were inferred from these measurements. At such temperatures, creep induces very large strains prior to the occurrence of the cracks which, in the worst-case scenario, can propagate at velocities as high as several meters per second. The design of the experiment enabled us to study the influence of the temperature (magnitude and hoop distribution), of the toughness of the steel (two grades were studied) and of the volume of pressurized gas. The results show that creep and crack propagation are highly dependent on temperature, and also that crack initiation and propagation are highly dependent on the degree of heterogeneity which is responsible for the localized initiation of the crack.