In-situ measurements of the depth profiles of tritium in a titanium tritide target for generating 14-MeV neutrons have been made with the method of the ion beam analysis using the T(d, α)n nuclear reaction. The initial distribution of tritium in the unirradiated target has been observed to be nearly uniform over the depths. After the irradiation of 390-keV Ds⁺ ions at a temperature of about 10°C a dip has been found in the depth profile around the depth of the projected range of the ions. By the successive isochronal annealings at temperatures below 130°C the tritium has been uniformly redistributed. The behavior of tritium in the target and the effectiveness of the depth profiling for evaluating the energy spectrum and the yield of source neutrons are discussed.

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A new formulation of energy-space dependent propagation of errors has been derived for the Monte Carlo-Monte Carlo coupling technique which is applied to analysis of radiation streaming through a long path. In this formula, it is considered that the source uncertainty due to the statistical error of the preceding Monte Carlo calculation is handed down to a particle as an uncertainty of the particle weight. In the succeeding Monte Carlo calculation, the propagated weight error is scored together with the particle weight by flux estimators. The method has been implemented in the MORSE-ALB code system. As a sample problem, calculation of reaction rates in the main pump room of the primary coolant system of JOYO is performed with the Sn-AMC-AMC coupling technique. As a result, the present method turned out to be significant in estimating the Monte Carlo statistical error of the final value taking into consideration of the energy-space dependence of error propagation.

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A new method has been established to calculate sensitivity coefficients of cell parameters based on generalized perturbation theory using the collision probability method. The proposed method does not require the calculation of the changes of collision probabilities due to cross section changes, so it is as powerful as the commonly used generalized perturbation theory in diffusion theory, We demonstrate the validity of the method by comparing the calculated sensitivity coefficients with those obtained from the direct cell calculations. As an application, we calculate the sensitivity coefficients of neutronic properties in cells with different moderator to fuel volume ratios, and discuss the physical meaning of the difference between the sensitivity coefficients.

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A new method has been established to calculate sensitivity coefficients of cell parameters based on generalized perturbation theory using the collision probability method. The proposed method does not require the calculation of the changes of collision probabilities due to cross section changes, so it is as powerful as the commonly used generalized perturbation theory in diffusion theory, We demonstrate the validity of the method by comparing the calculated sensitivity coefficients with those obtained from the direct cell calculations. As an application, we calculate the sensitivity coefficients of neutronic properties in cells with different moderator to fuel volume ratios, and discuss the physical meaning of the difference between the sensitivity coefficients.
With the analysis of hypothetical accident in a nuclear power reactor, a molten fuel and coolant interaction (MFCI) leads a vapor explosion under certain circumstances. The author has performed fundamental experiment on the vapor explosion with a mass of grains of certain particle sizes which simulate the molten fuel fragments, to verify the relation between the particle size and the magnitude of pressure pulses.
The standard temperatures of water and liquid nitrogen used as cold liquid set prior to the test are 25°C and 77 K respectively, and that of grains (SiC) are 600°C for the former and 25°C for the latter experiments. For both experiments, the maximum pressure pulse has the greatest value at the grain size of 0.27 mmφ. This value of diameter agrees approximately with the median of the size distribution of the fragments measured in some vapor explosion experiments with a hot molten metal.
In the results of using water as cold liquid, boiling pressure traces show the oscillations of higher frequency than 100 Hz with particle sizes ranging 0.20.5 mm. The initial temperatures of grains and water little effect on generating such oscillations as far as it is tested in this study.

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For gaining basic data on decay heat coolability of debris bed in the post-accident heat removal, measurement of dryout heat flux was made, with stagnant water as coolant, in a 50 mm I. D. pyrex glass cylinder vessel. The fuel debris bed subjected to decay heat was simulated by steel ball particles which were inductively heated with a power supply of 20 kHz and 30 kW. The bed was made of homogeneous size particles. An emphasis was placed on the influence of system pressure and particle size. The experiment covered the ranges over the steel ball diameters of 0.34.0 mm and the system pressure of 0.020.5 MPa.
The experimental results, as a whole, agreed fairly well with the prediction based on Lipinski's 0-D model with respect to the dependence of dryout heat flux both on pressure and on particle size. In detail, however, the dryout heat flux deviates toward a lower value at a higher pressure while to a higher value for a smaller size particle bed. Comparison of the results between the free and fixed beds suggests that the deviation to the higher side will be attributed to the channeling and/or levitation.

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The conditions for producing mixed Th0₂-UO₃ sols with 040% U by neutralizing nitrate solutions with ammonia solution under pH control are studied. With 035% U, good source sols for gelation in CCl₄-ammonia media are obtained. Colloid fraction of U in producible stable sols is lower than that of Th. The former, moreover, decreases considerably with increase in U content while the latter does only a little ; this results abrupt decrease in their colloid fraction of (Th+U) with increase in U content. Whether gelation behavior of such sols is good or not depends on fraction of 4.1 nm or larger colloids, and on U content. The minimum value of the colloid fractions resulting no gel-sphere failure also decreases with increase in U content. The gel-sphere failure is a crack for lower U content and a hole like a dimple or a navel for higher one. The difference is also discussed.

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Solvent extraction of Co with diethyldithiocarbamate (DDC) has been applied to the determination of the chemical state of Co in OWL-1 loop water installed in JMTR. The 7593% of the "soluble" ⁶⁰Co are in a form to be easily extracted, Co(II)²⁺, and 522% are in a form being transformed to an extractable form at pH 5.5. The rest, a few percent, is in non-extractable state, possibly in a fine particle. These results are consistent with the general concept that majority of ⁶⁰Co in "soluble" fraction is in a state of Co (II)²⁺ in the primary coolant of nuclear reactor. It is also noticed that in contact with air in alkaline media a slow oxidation of Co (II) (OH)₂ to Co (III) (OH)₃ tends to occur at an apparent oxidation rate of
-d[ Co (II)]/dt=k[ Co (II)][O₂]^1/4.
This oxidation leads to the decrease of the extractability.

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The effect of iron on the colloidal behaviors of americium in near-neutral solutions was studied by applying the ultrafiltration method to americium (²⁴¹Am) solutions, iron (⁵⁹Fe) solutions and americium/iron mixed solutions. The concentration of americium was typically about 10^-9M and that of iron 10^-7M. Some properties of colloidal particles were deduced from the particle-size distributions. It was revealed that the colloidal americium particles may represent pseudo colloids, which behave together with iron true colloids.
The proposed simple model, in which the iron true colloid is assumed to be a chain-like polymer composed of hydroxide, is able to describe the particle-size distribution of iron colloids observed in this work. It was also found that the adsorption of americium and iron on the vessel walls depends on the particle-size distributions.

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The natural background r-radiation was observed by 102.88 cc lithium drifted germanium detector. Twenty-five lines due to 228Ac were observed in the energy spectrum extending from 50 to 1, 280keV. Comparison with other workers led to identifying two unknown peaks and observing four new lines. A quantitative measurement of the peaks is given in terms of relative intensity of the observed γ-lines.

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In a High Conversion PWR (HCPWR), the neutron spectrum is hardened in comparison with the conventional PWR and the nuclear characteristics of the control rod is much different. We have calculated the control rod worth in a HCPWR for several materials of strong neutron absorbers and selected B₄C for the control rod material. For the B₄C control rod, we have investigated the various nuclear characteristics such as the spatial and energy dependency of neutron absorption, the dependency of the control rod worth on moderator to fuel volume ratio and Pu enrichment etc., and obtained the useful data for the nulear design of control rods in a HCPWR.

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It is believed that pellet-cladding in-teraction (PCI) of light water reactor fuel has a potential to cause failure. To understand the PCI induced fuel failure (PCI failure), it is first necessary to understand the phenomenon of microscopic crack initiation and propagation (CIP) which initiates from the internal surfaces of Zircaloy cladding.
To date, however, there have been many technical difficulties with direct CIP measurement of an irradiated fuel rod. The Halden Project has recently developed a technique with eddy-current test (ECT) which allows direct measurement of the CIP phenomenon. The use of in-pile ECT technique itself is not unique and has been used widely(1)(9).
However, the application of ECT to in-pile experiments to detect CIP phenomenon leading to PCI failure, is new. This paper describes the first results of ECT on in-pile experiments carried out at the Halden Boiling Water Reactor (HBWR).

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High-level waste (HLW) glass which contains hazardous fission products and actinides should be isolated from the biosphere. One isolation method is disposal in geologic formations. The contact of groundwater with the HLW glass will be a trigger for waste radionuclides to move into the biosphere. Therefore an extensive study of the leaching behavior of HLW glass in groundwater is necessary.
The in-situ burial leach tests carried out in Japan provided several results on leaching behavior of simulated HLW glass in natural groundwater. For example, uneven leaching occurred in natural groundwater, which resulted in the formation of many grooves on the originally flat surface of the glass⁽¹⁾⁽²⁾. This result was found in an experiment carried out at a low temperature of 14°C, and we have not yet confirmed whether or not such uneven leaching occurs at relatively higher temperatures.
In the present study, we showed that the leaching behavior of simulated HLW glass at 14°C in one type of natural groundwater in Japan was quite similar to that which occurred at 70°C in the synthesized groundwater in two ways ; uneven leaching and precipitation.

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