Yoshiyuki Kihara

Physical Properties and Irradiation Behavior Analysis of Np- and Am-Bearing MOX Fuels

The physical properties and irradiation behavior of Np- and Am-bearing MOX were evaluated for the development of advanced fast reactor fuels. The physical properties, lattice parameter, melting temperature, thermal conductivity, and oxygen potential of the fuels were described as functions of Np content, Am content, and oxygen-to-metal (O/M) ratio, and the effect of a few percent Np and Am addition into MOX on those properties was found to be negligibly small. The irradiation tests of fuel pellets having O/M ratios of 1.98 or 1.96 were carried out at a high linear heat rate of about 430 W/cm for 24 h. The redistributions of actinide element and oxygen were analyzed by using the physical properties for Np- and Am-bearing MOX, and the maximum temperatures of the pellets were estimated. The maximum temperatures of the pellets of O/M = 1:96 and 1.98 were estimated to be 2,701 and 2,510 K, respectively. The analysis result showed that the higher maximum temperature in the low-O/M pellet was caused by the low thermal conductivity in the outer region of the pellets, and the maximum temperatures of the pellets did not exceed their melting temperatures. In the results of postirradiation examination, no trace of melting was observed.

FUJI, an Initial Sintering Comparison Test for Pelletized-, Sphere-Pac- and Vipac-Fast Breeder Reactor Mixed Oxide Fuel

Options for fuel cycle technology improvement have strongly regained attention lately with the revival of nuclear energy production interests and plans for next generation nuclear systems. Various fuel forms, geometries and production paths are being looked at. Within the FUJI collaboration program among Japan Atomic Energy Agency (JAEA, former JNC), Paul Scherrer Institute (PSI, Switzerland) and Nuclear Research and Consultancy Group (NRG, the Netherlands) the production paths of plutonium and neptunium mixed oxide- (sphere-pac- and vipac-) particle fuels (20 wt% Pu, 5 wt% Np and 75 wt% U) are tested as well as the initial sintering and power-to-melt behavior under simulated Fast Breeder Reactor (FBR) conditions. The various fuel forms were produced at PSI under the support of JNC, the irradiations were accomplished at High Flux Reactor (HFR) in Petten, the post irradiation examinations are being achieved mainly at NRG and the fuel modelling being performed at JNC and PSI. The present paper reviews mainly the project planning, fuel behaviour-pre-calculations and the fuel- and fuel segment-production. A short overview of the irradiation conditions and ceramographic post irradiation examination analyses is also given.

Fuel performance of hollow pellets for fast breeder reactors

Three fuel rods containing hollow mixed oxide (MOX) pellets of uranium and plutonium oxides were fabricated and irradiated at a high linear heat rate (LHR) to burn-up of nearly 30,000 MWd/t in the experimental fast rector, JOYO MK-II. After irradiation, one of the fuel rod pellets was examined by X-ray CT and conventional nondestructive and destructive methods. Swelling rate was evaluated by both dimensional change and radial density distribution. There were no differences between both types of results and it was concluded that swelling rate can be examined in detail by the X-ray CT technique without dismantling the assembly. In addition, the swelling rate of hollow pellets was nearly the same as values reported for the fuel rods containing solid pellets. LHR was higher in the examined fuel rod containing hollow pellets than in the conventional fuel rod containing solid pellets, but fission gas release rates for both fuel rods were nearly the same.

Phase states in the Pu-Si-O ternary system

The phase states in the Pu-Si-O ternary system were investigated to understand the behaviour of Si impurity in MOX fuel and to assist in evaluating acceptable amounts of Si impurity in the fuel. Samples, which were mixed powders of PuO2 and SiO2 in three molar ratios, were annealed at 1623K-1973K as a function of oxygen potential. Two (Pu, Si) compounds, Pu4.67Si3O13 and Pu2Si2O7, were precipitated by annealing under a reducing atmosphere. The Pu4.67Si3O13 phase was precipitated in a wider composition range as compared with Pu2Si2O7.

Vibro-Packing Experiment of Non-Spherical Uranium Dioxide Particles with Spherical Metallic Uranium Particles

Japan Atomic Energy Agency has developed vibro-packed fuel as one of the candidates for commercial fast breeder reactor fuels. In this study, vibro-packing experiments were carried out to investigate particle movement during vibro-packing as well as particle distribution after the completion of vibro-packing. Non-spherical uranium dioxide particles and spherical metallic uranium particles were used to simulate mixed oxide particles and oxygen getter particles, respectively. These experiments revealed the following facts. It is important to prevent segregation by means of feeding each size of the fuel particles uniformly into a cladding tube in order to disperse oxygen getter particles uniformly. “Simultaneous feeding” with volumetric powder feeders is useful to realize the above.

Study on Boiling Behavior of Solution by Microwave Heating

At present, several programs for mass production of MOX bulk are on going. The MOX bulk is the capacity of the container to be used to generate MOX fuel. One of them is the selection of the vessel configuration for efficient evaporation of large amount of solution. Two types of vessel as shallow and cylindrical, are under examinations. The shallow vessel has been successfully cleared examinations in moderate running with no flushing, but the amount of products per batch is rather small. On the other hand, the cylindrical vessel is newly proposed with the intent of increasing the production capacity per batch, but has flushing the solution from the top of the vessel by the Microwave Heating (MH). Elucidation on the mechanism of dynamic behavior of the flushing and spilling is our purpose of study. It was carried out by designing a equipment which imitated the practical setup for microwave heating. A visual observation was conducted to clarify the mechanism of dynamic behavior on the sudden nucleation of the solution in the deep cylindrical vessel under MH. The experiment was continued by changing the height and the shape in order to perform the effect evaluation of the size and the shape of vessel.Copyright