Recently, the multi-point reactors kinetics equations were derived rigorously from the time dependent neutron transport equation using the region-wise importance functions for the production of fission neutrons.
In the present work, the kinetics parameter lm used in those equations is shown to have a physical meaning of the region-wise neutron generation time.

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A timing verification system for analogue relay circuits has been developed. The verification is performed by Time-Symbolic Logic (TSL) simulation that allows symbolic representation of the time. With representation of the relay actuation time by time-variables, TSL simulation can simulate all possible behaviors that differ with the timing of relay action. To reduce the simulation cost, the simulation technique was improved using the characteristics of the relay circuits. Users can verify the circuit behavior without preparing numerous simulation inputs or executing numerous simulation cases.
The developed system was applied to the verification of actual circuits. The circuit behaviors with all the possible timings under the realistic constraints were simulated and verified. These application studies confirmed that the developed system is useful and effective.

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A Finite Variable Difference Method (FVDM) proposed previously by the author for locally exact numerical schemes is extended so as to be applicable to polynomial expansion schemes. This extended FVDM is applied to the QUICK scheme.
The optimum differencing points are analytically derived in terms of mesh Reynolds numbers so that the variance of the numerical solution is minimized under the condition that roots of the resulting characteristic equation are nonnegative to insure the numerical stability. This optimized scheme coincides with the original QUICK scheme at Rm=8/3, which is the critical value of its stability, and complements a stable scheme for Rim greater than 8/3. This optimization improves the numerical solution for the steady and unsteady convectiondiffusion equations without numerical oscillations.
In the same manner as the previous result for the locally exact numerical schemes, it has been made clear based on the extended FVDM that optimum differencing points from the view point of numerical stability and accuracy exist for the polynomial expansion schemes.

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Chromium depletion near grain boundaries of austenitic stainless steel during irradiation was investigated. Specimens were kept at 1, 473 K for 30 min, and were quenched into the water. Irradiations were done using 400 keV He+ ions at 573, 673 and 773 K up to 10 dpa with a dose rate of 2.4 ×10-4 dpa/s. After irradiation, the Cr concentration profile near the grain boundary was measured using an analytical electron microscope with a 1 nm beam diameter. At 573 K, Cr depletion is small, and its concentration at the grain boundary decreases to 15.5 mass% at 3 dpa from the initial concentration of 18.5 mass%. At 673 and 773 K, Cr concentration at the grain boundary rapidly decreases between 0 and 0.2 dpa, and then gradually approaches a constant value, 7.0 mass% at 673 K and 5.0 mass% at 773 K. Two stages are found in radiation induced segregation (RIS) behavior, one stage in which Cr depletion and Ni enrichment balance and another in which Fe depletion and Ni enrichment balance.
These experimental results were compared with the calculations based on the vacancy-induced inverse Kirkendall effect. Predicted Cr segregation at 673 and 773 K above 3 dpa agrees with the experimental results. But Cr depletions at low doses which were obtained in the experiments are much faster than calculated. At 573 K in the experiments, depletion is smaller than calculated up to 10 dpa.

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This study is related to the development of a suitable mixture of citric acid, EDTA and ascorbic acid (CEA) for dissolving the haematite deposited on the structural surfaces of cooling water circuits in BWRs. The dissolution experiments were performed with synthetically prepared haematite. The dependence of the dissolution rates on each of the constituents of the mixture has been evaluated using a 'grain model'. It was found to be Langmuirian in the case of citric acid, linear in the case of EDTA and independent of ascorbic acid concentration. The ratio of molar concentration of the ligand to the total iron was varied from 0.5-2.5. Activation energy of the dissolution in a CEA mixture having stoichiometrically excess EDTA has been determined by performing experiments upto 353 K. The highest dissolution was obtained in 11:44:4 mol•m-3 and 2:55:4 mol•m-3 CEA mixtures.

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Radiolytic oxidation behavior of neptunium was investigated in order to predict its migration behavior at the disposal site for radioactive waste. Neptunium, in 5 mol/dm3 sodium chloride solutions of several pH values, was irradiated by α-particles of 238Pu which had been placed in the solutions as dioxide powder. Solution neptunium redox behavior was compared with that of an unirradiated sample. Pentavalent neptunium, which was stable in the absence of 238Pu, was found to be oxidized to hexavalent and even to heptavalent neptunium. Oxidizing species would be chloride molecule anion (Cl2- ) and/or hypochlorite anion (CiO-) which were generated by the reaction between radiolytically generated hydroxide radical (OH) and chloride ion (Cl-). The oxidation rate of pentavalent neptunium was independent of its concentration, but dependent on solution pH. The measured rate constant was (19±4) [H] mol/dm3/d.

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The effective tritium system should be designed to recover tritium from DT reactor blanket sweep gas in a form that is easy to transfer to the main fuel cycle. The cryosorption method using a porous adsorbent at the temperature of liquid nitrogen is one of the candidate processes for extracting tritium from the sweep gas. For designing of a cryosorption column for recovery of tritium from hydrogen-swamped helium sweep gas, it is necessary to predict the breakthrough curve for mixture of multicomponent hydrogen isotopes in helium. In this report, a method to calculate the breakthrough curve at cryosorption of multicomponent hydrogen isotopes on molecular sieve 5A, molecular sieve 4A or activated carbon at 77.4 K is presented.

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Palladium membrane has been studied for sepration and purification of hydrogen isotopes because of its large permeability. In order to consider permeation of mixture of hydrogen isotopes, solubilities of protium and deuterium in palladium were studied in the temperature range of room temperature to 500°C using breakthrough method. It was observed that solubilities were represented by Sieverts' law and that the separation factor of protium-deuterium binary system was different from the isotope effect ratio. The ideal adsorbed solution theory by Myers and Prausnitz can be applied to estimate the separation factor of protium-deuterium binary system in palladium using the isotope effect ratio observed when protium and deuterium are handled independently. The permeation behavior of multi component hydrogen isotopes through palladium membrane is discussed applying observation on solubilities of this work.

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Solid forms fixing nuclides were produced from Cs-mordenite and Sr-zeolite A by calcination at 1, 200°C for 1 h. Cesium and strontium were uniformly dispersed in pollucite (CsAlSi2O6) and Sr-feldspar (SrAl2Si2O8), respectively. Compressive strength of the products increased with decreasing particle size of starting zeolites, yielding the value above 1.2 GPa for the Cs product. Thermal conductivities of Cs and Sr products were measured to be about 1.0 and 0.6 W/(m•K), respectively. Leachability of Cs was in the order, 0.1 M HNO3>0.1 M NaOH>0.1 MNaCl>deionized water. The Sr product had lower leach rate compared with the Cs product, and no Sr was detected in deionized water up to 90°C

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