Fission product kinetic energies were measured by the double-energy method for thermal-neutron fission of 235, 233U and proton-induced fission of 238U at the 15.8-MeV excitation. From the obtained energy-mass correlation data, the kinetic-energy distribution was constructed from each mass bin to evaluate the first moment of the kinetic energy for a given fragment mass. The resulting kinetic energy was then converted to the effective distance between the charge centers at the moment of scission. The effective distances deduced for the proton-induced fission was concluded to be classified into two constant values, one for asymmetric and the other for symmetric mode, irrespective of the mass though an additional component was further extracted in the asymmetric mass region. This indicates that the fission takes place via two well-defined saddles, followed by the random neck rupture. On the contrary, the effective distances obtained for thermal-neutron induced fission turned out to lie along the contour line at the same level as the equilibrium deformation in the two-dimensional potential map. This strongly suggests that it is essentially a barrier-penetrating type of fission rather than the over-barrier fission.

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Analyses of an equilibrium cycle are useful for evaluating newly designed fuels, defining an envelope of core operating parameters, and so on. However, generation of a loading pattern for the equilibrium cycle is much more difficult than that of a single cycle. Therefore, a loading pattern optimization code for the equilibrium cycle of pressurized water reactors, OPAL, has been newly developed on the basis of the simulated annealing method. In order to verify the capability of the OPAL code, comparison with successive multicycle optimizations was performed while fixing the number of fresh fuel in each cycle. Through benchmark calculations, it was found that the result of the equilibrium cycle optimization was almost compatible with that of the successive multicycle optimization, when the definition of each objective function was similar. However, successive multicycle optimization includes some ambiguity due to limits on the number of calculated cycles, since it requires much computation time. Consequently, the equilibrium cycle optimization has advantages including the quantitative comparison of the core neutronic performances.

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Superconducting tunnel junctions in use for X-ray detection are expected to produce an excellent energy resolution. An inclusive model is employed to give an overview of the detector characteristics. This method is devised to implicitly take properties of superconductor materials into account. With introducing an empirical relationship between junction parameters, the detector characteristics such as signal magnitude and energy resolution are reproduced to an acceptable degree. This method gives a helpful suggestion for understanding the detector performance such as a Fano-like factor, and may also serve as a guide line for designing tunnel junctions.

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Based on the result of micro-gamma scanning of a fuel pin irradiated to high burnup in a commercial PWR, the radial distribution of chemical forms of fission products (FPs) in LWR fuel pins was theoretically predicted by a thermochemical computer code SOLGASMIX-PV. The absolute amounts of fission products generated in the fuel was calculated by ORIGEN-2 code, and the radial distributions of temperature and oxygen potential were calculated by taking the neutron depression and oxygen redistribution in the fuel into account.
A fuel pellet was radially divided into 51 sections and chemical forms of FPs were calculated in each section. In addition, the effects of linear heat rating (LHR) and average O/U ratio on radial distribution of chemical form were evaluated.
It was found that approximately 13mole% of the total amount of Cs compounds exists as CsI and virtually remaining fraction as Cs2MoO4 under the operation condition of LHR below 400W/cm. On the other hand, when LHR is beyond 400W/cm under the transient operation condition, its distribution did not change so much from the one under normal operation condition.

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A specific heat treatment process that introduces hoop stress has been developed. This technique can produce zirconium alloy tubing with a residual compressive hoop stress near the inner surface by taking advantage of the mechanical anisotropy in hexagonal close-packed zirconium crystal.
Since a crystal having its basal pole parallel to the tangential direction of the tubing is easier to exhibit plastic elongation under the hoop stress than that having its basal pole parallel to the radial direction, the plastic and elastic elongation can coexist under a certain set of temperature and hoop stress conditions. The mechanical anisotropy plays a role to extend the coexistent stress range. Thus, residual compressive hoop stress is formed at the inner surface where more plastic elongation occurs during the heat treatment.
This process is referred to as expanded heat treatment. Since this is a fundamental crystallographic principle, it has various applications. The application to improve PCI/SCC (pellet cladding interaction/stress corrosion cracking) properties of water reactor fuel cladding is promising.
Excellent results were obtained with laboratory-scale heat treatment and an out-reactor iodine SCC test. These results included an extension of the time to SCC failure.

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Our earlier investigations have shown that the dissolution of moderately sintered haematite in a reductive-complexing formulation containing citric acid, EDTA and ascorbic acid (CEA) in the initial concentration ratio of 11:44:4 mol•m-3 (initial pH 2.8) is faster than at other concentration ratios. The dissolution was considered for a system having a surface area to volume ratio of 67m-1 with oxide thickness of 5μm, a system volume of -8.5m3 and no regeneration of chelant. In the present work different reducing agents in place of ascorbic acid and different chelating agents in place of EDTA have been studied, keeping the citric acid-complexing agent-reducing agent concentration ratio the same as above, to find out their relative effects on the dissolution process and to identify that formulation which gives the fastest dissolution. It is found that among the different formulations studied, CEA is the best for the dissolution of moderately sintered haematite particles.

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In order to raise ion extraction efficiency in laser isotope separation, we have developed a radio-frequency (rf) resonance method. Then, to confirm feasibility of this method to a photoionized plasma, we experimentally studied the ion extraction characteristics.
When the rf frequency was swept under a weak magnetic field (5mT), the plasma-sheath resonance was found to occur at about 12MHz which was almost the same value as the theoretical one. Moreover, it was confirmed that the ion extraction time at the resonance frequency became the minimum.
When the magnetic field strength decreased from 5mT to zero, the ion extraction time became long. From the simulation results, this was because the plasma potential decreased with the magnetic field strength. Therefore, a magnetic field strength of more than 1mT was required to obtain a sufficient ion extraction efficiency.
To obtain the same extraction time as when applying a -3kV dc voltage in the electrostatic method, the rf resonance method needed a voltage more than 70Vrms, in which the dc bias was -1kV. Therefore, we confirmed that this method is feasible for the ion extraction from the photoionized plasma.

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The use of an activated charcoal sampler for radon monitoring has become popular in recent years because of its passiveness and low price. Dynamics of adsorption on a passive sampler have been described with theoretical models. However, extrapolation of the measured results of radon on charcoal to the diurnal fluctuations of the ambient radon concentration is often difficult and even misleading because of the oversimplification of these models. A more generalized approach is undertaken by treating the diurnal variations in radon concentrations as poly-exponential functions and by solving for explicit particular solutions of Fick's equation. The application of these solutions to various practical situations is explored. This includes their use for charcoal sampler calibration. Estimated values of the adsorption coefficients, k, and diffusion constant, D, appear to be agreeable with corresponding reported values. A triple-sampler protocol is also proposed for radon survey in areas of high diurnal fluctuations.

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In this paper, we propose different alternative approaches to optimize the subspace iteration method which obtains the dominant λ-modes of a nuclear power reactor. We present a variational acceleration for the iterative process, a coarse grain parallelizatization approach, and a multistep algorithm to choose efficient initial estimations for the subspace iteration method. We have tested the efficiency of the developed algorithms with a 3D realistic problem, corresponding to a static configuration of the reactor Ringhals I.

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In order to cause fewer environmental impacts, nuclear power plant systems and operational procedures with fewer radwaste sources, lower occupational exposures and smaller operational areas contaminated by radioactivity which will minimize internal exposure, have been established. Collaborative efforts have demonstrated that the combined application of major improvements in the systems and better operational procedures (e.g., (1) prevention of fuel defects, (2) application of low cobalt containing and corrosion resistant materials for the primary cooling system, (3) improvement of condensate water cleanup system and the resins applied to it, and (4) careful water chemistry control) is resulting in BWRs involved in the Japanese Improvement and Standardization Program (JISP BWRs) having occupational exposure of less than 0.5man•Sv/yr, minimized contaminated areas in turbine buildings to only around the main steam turbines, and radwaste sources pro-ducing fewer than 500drums/yr. Additionally, the JISP BWRs have high reliability with more than a 75% duty factor and unscheduled plant shudown occurrences of fewer than once in 10 years.

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