[en] We report (1) the current status of neutrino parameters and (2) our recent work on implications of particle's coherence, which are weakly related each others. In the first part, current status of the neutrino parameters obtained from oscillation experiments and their prospects are briefly reviewed. From various oscillation experiments, existence of three mass scales have been confirmed. One value of the difference of mass squared is around 10^-3eV² and another is around 10^-5eV². Although mixing angles are partly found, one important angle, θ₁₃ is left unknown.In the second part, implications of coherence length of particles in the scattering of ultra-high energy cosmic rays (UHCR) with cosmic background radiations (CBR) is discussed. Although coherence length is regarded usually irrelevant to observations, its role is important in several situations of recent experiments which include that of the ultra-high energy charged particles. Here we discuss the scattering of UHCR with CBR

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[en] To establish reasonable safety concepts for the realization of commercial liquid-metal fast breeder reactors, it is indispensable to demonstrate that the release of excessive energy due to re-criticality of molten core could be prevented even if a severe core damage accident took place. Two-phase flow due to the boiling of fuel-steel mixture in the molten core pool has a larger liquid-to-gas density ratio and higher surface tension in comparison with those of ordinary two-phase flows such as air-water flow. In this study, to investigate the effect of the recirculation flow on the bubble behavior, visualization and measurement of nitrogen gas-molten lead bismuth in a rectangular tank was performed by using neutron radiography and particle image velocimetry techniques. Measured flow parameters include flow regime, two-dimensional void distribution, and liquid velocity field in the tank. The present technique is applicable to the measurement of velocity fields and void fraction, and the basic characteristics of gas-liquid metal two-phase mixture were clarified

[en] In the SCARABEE BF2 test, a boiling pool of pure UO₂ was formed in a crucible of 6 cm diameter in the in-pile safety test reactor SCARABEE. A SIMMER-III computer code was successfully applied to this test analysis and well reproduced the pool boiling behavior, such as heat flux distribution along the crucible wall, the location of pool surface and its oscillative behavior, cover gas pressure, and the fuel crust thickness on the crucible surface. This study has confirmed the applicability of SIMMER-III to an internally-heated boiling pool. Some insights were also obtained into those phenomena in the BF2 test which were not directly recognized by experimental measurement alone: void distribution and transient flow behavior inside the pool and the mechanism of temperature fluctuation at the crucible surface. Finally, parametric calculations were carried out to clarify the mechanisms which produced the oscillation of the boiling pool in BF2. It was shown that the effect of heat losses to the wall was relatively small, and rate of vapor bubble growth in the pool had a significant effect on the boiling behavior. (author)

[en] This paper describes major research subjects and approaches on reactor safety for commercialization of fast reactors including recriticality issue in core disruptive accident sequences. To achieve the research objective for these major subjects, a new in-pile safety experimental program named SERAPH (safety engineering reactor for accident phenomenology) is proposed, and the conditions of the proposed tests and the major requirements for the facility are formulated. 13 refs., 5 figs., 1 tab

[en] The development of a SIMMER-III computer code is in progress to investigate postulated severe accidents in liquid-metal fast breeder reactors (LMFBRs). SIMMER-III is a two-dimensional, three-velocity-field, multiphase, multicomponent, Eulerian, fluid-dynamics code coupled with a space- and energy-dependent neutron dynamics model. In order to model complex flow situations in a postulated disrupting core, mass and energy conservation equations are solved for 27 density components and 16 energy components, respectively. Three velocity fields (two liquids and one vapor) are modeled to simulate relative motion of different fluid components. In this paper, the models, numerical algorithms and code features of SIMMER-III are discussed along with example calculations, emphasizing the fluid-dynamics portion of the code. The SIMMER-III code is expected to significantly improve the flexibility and reliability in LMFBR safety analyses. (author)

[en] The main purpose of the SIMMER-III code is to provide a numerical simulation of complex multiphase, multicomponent flow problems essential to investigate core disruptive accidents in liquid-metal fast reactors (LMFRs). However, the code is designed to be sufficiently flexible to be applied to a variety of multiphase flows, in addition to LMFR safety issues. In the present study, some typical experiments relating to fuel-coolant interactions (FCIs) have been analyzed by SIMMER-III to demonstrate that the code is applicable to such complex and highly transient multiphase flow situations. It is shown that SIMMER-III can reproduce the premixing phase both in water and sodium systems as well as the propagation of steam explosion. It is thus demonstrated the code is basically capable of simulating integral multiphase thermal-hydraulic problems included in FCI experiments. (author)

[en] An experimental study was done to investigate characteristics of metal-water interaction, when a mount of hot liquid metal is injected into the water. The test section is a vertical shock tube of 60mm in inner diameter and 1200mm in length. A special injector which is designed to inject hot metal of controlled volume and flow rate is attached at the top of the tube. When the hot metal is injected in the water and comes down at a position of the test vessel, a trigger pressure pulse is generated at the bottom of the test tube. Local transient pressures along the tube are measured by piezo pressure transducers. The following items were investigated in the experiment; 1) The criteria to cause a vapor explosion, 2) Transient behaviors and propagation characteristics of pressure wave in the mixing region. 3) Effects of triggering pulse, injection temperature and mass of hot molten metal on the peak pressure. The probability of the vapor explosion jumped when the interface temperature at the molten metal-water direct contact is higher than the homogeneous nucleation temperature of water and the triggering pulse becomes larger than 0.9MPa. Two types of the pressure propagation modes are observed, one is the detonative mode with a sharp rise and other is usual pressure mode with a mild rise. (author)

[en] The present report gives the SIMMER-III heat- and mass-transfer model describing melting/freezing and vaporization/condensation processes in multiphase, multicomponent systems. The heat- and mass-transfer processes are modeled in consideration of their importance in and effects on the behavior of reactor-core materials in the fast reactor safety analysis. Applying equilibrium and non-equilibrium transfers generalizes the phase-transition processes except for the structure breakup transfer. The non-equilibrium transfers occurring at interfaces were formulated on the basis of the heat-transfer-limited model. The implicit solution algorithm for basic vaporization/condensation equations is tightly coupled with the analytic equation-of-state (EOS) model. The use of this approach successfully solves numerical problems encountered in the previous codes, which were mainly introduced by thermodynamic inconsistencies in EOS. (author)

[en] An advanced safety analysis computer code, SIMMER-III, has been developed to investigate postulated core disruptive accidents in liquid-metal fast reactor (LMFRs). SIMMER-III is a two-dimensional, three-velocity-field, multiphase, multicomponent, Eulerian, fluid-dynamics code coupled with a space-dependent neutron kinetics model. By completing and integrating all the physical models originally intended at the beginning of this code development project, SIMMER-III is now applicable to integral reactor calculations and other complex multiphase flow problems. A systematic code assessment program, conducted in collaboration with European research organizations, has shown that the advanced features of the code have resolved many of the limitations and problem areas in the previous SIMMER-II code. In this report, the models, numerical algorithms and code features of SIMMER-III Version 3.A are described along with detailed program description. Areas which require future model refinement are also discussed. SIMMER-III Version 3.A, a coupled fluid-dynamics and neutronics code system, is expected to significantly improve the flexibility and reliability of LMFR safety analyses. (author)