Methodological errors in the precise measurement of γ-ray energies with Ge detectors are examined basing on a model of photopeak shape function. The model revealed that the centroid of the normal distribution embedded in the phenomenal photopeak is to be compared with the energy scale. The peak difference rate is introduced to evaluate the peak difference, the essential quantity of experimentally giving secondary energy standard, relative to the energy difference. Varied value of the gap difference-rate index with several physical parameters has indicated that the secondary γ-ray energies have a definite amount of methodological errors. A typical methodological error in the γ-ray energy at around 300 keV is in the range of -263±125 -54 ± 123 eV (or -877 ± 418-180 ± 411 ppm). Commonly used "conventional" energy-calibration methods by the use of the most probable peak-height position have been reviewed. Origins of methodological errors are discussed. A new energy-calibration method using the centroid is proposed.

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Neutron-induced activity in the PCA austenitic stainless steel is examined, when used for first-wall components in a DEMO fusion reactor. Some low-activity definitions, based on different waste management and disposal concepts, are introduced.
Activity in the PCA is so high that any recycling of the irradiated material can be excluded. Disposal of PCA radioactive wastes in Shallow-Land Buriable (SLB) is prevented as well. Mo, Nb and some impurity elements have to be removed or limited, in order to reduce the radioactivity of the PCA. Possible low-activity versions of the PCA are introduced (PCA-la) ; they meet the requirements for SLB and may also be recycled under certain conditions.

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To develop a real time and in-situ process gas analyzer for fusion fuel gas processing systems, application study of laser Raman spectroscopy was performed by measurement of hydrogen isotopes. Using an Ar ion type laser of which wavelength 488 nm, power 0.7 W, and single pass irradiation method, Raman spectra of hydrogen isotopes were measured and intensities of the Stokes rotational lines and Q-branch were quantitatively analyzed. The Stokes rotational lines at 587, 443 and 415 cm^-1 were selected as suitable ones for quantitative analysis of H₂, HD and D₂. Normalizing the Raman intensity of partial pressure H₂ as 100, relative Raman intensity ratio of H2: HD: D₂ was obtained as 100: 58: 47. The detection limit for hydrogen was estimated as 0.05 kPa in partial pressure and 500 ppm in concentration. But multiple pass method further improved the detection limit to 100 ppm.

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Ethylene diamine tetra acetic acid (EDTA) is a versatile complexing agent and is being employed in decontamination formulations. The dilute chemical decontamination (DCD) process employs ion exchange resins for regeneration of complexants, collection of metal ions/active isotopes and for removal of the decontaminating chemicals. In this work the interactions of EDTA on cation and anion exchange resins have been studied. The pickup of EDTA on cation exchange resin is by ion exchange mechanism and not possibly by precipitation at the low pH existing in ion exchange resin matrix. A mathematical relationship has been worked out to calculate the amount of EDTA adsorbed per unit volume of the cation exchange resin at a given pH. In addition, the behaviour of DTPA, HEEDTA and NTA on cation exchange resin has been evaluated. The chromatographic behaviour of OH- form of strong base anion exchange resin for a formulation containing EDTA, oxalic acid and citric acid has been reported and its relevance to the decontamination process has been discussed.
Even though the corrosion rate of DCD is very low on most of the materials of construction, influence of time, temperature and the composition of the formulation on carbon steel is studied. Different classes of inhibitors were evaluated for reducing carbon steel corrosion.

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A sorption-desorption process using potassium-graphite intercalation compound (K-GIC) was studied to verify its applicability to hydrogen isotope separation. Lowly concentrated tritium (7.55 MBq/mol-H₂) contained in about 1 l of H₂ gas was successfully enriched using 1 g of KC₂₄. Three cycles of the sorption-desorption process applied to the H₂-HT gas mixture proved to enhance the tritium concentration by a factor of 3.9, with a concomitant reduction of volume to 1/14. The positive result obtained in this study promises for this type of sorption-desorption process using K-GIC very good prospects of useful application to hydrogen isotope separation. The experimental process was simulated by calculation based on the material balance of the two components, using data of equilibrium in single stage. The calculated values agreed very well with experimentally determined data, thus attesting the applicability of the above simulation procedure to designing K-GIC hydrogen isotopes separators.

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As a part of the study to expand the computational region of SPEEDI (System for Prediction of Environmental Emergency Dose Information), a mass-consistent wind field model developed for the local or mesoscale wind field was improved for the calculation of synoptic wind field. The major modification is the consideration of earth's curvature, The values of computational parameter were reexamined. This model was applied to the calculation of three-dimensional wind fields over Europe in the case of Chernobyl accident. The calculated horizontal wind fields agreed well with patterns of surface pressure and 850 mb geopotential height. The cyclonic winds around low pressure regions and the anticyclonic winds around high pressure regions were successfully computed by the model. The distribution pattern of calculated vertical wind roughly correlated with the surface weather chart.

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This paper describes the prototype light-duty telerobotic system constructed as a cold test facility in the program of developing technology for robotic handling systems to be used for decommissioning of nuclear reactors. The total system consists of a multi-functional, electric manipulator system, a transporter system of telescopic boom type, a monitoring system comprising several TV monitors and a computer-assisted control system for overall system operation. The slave manipulator has a load capacity of 10 daN and can be used both in air and in water. Various tests such as basic performance test and remote operability test have been performed to point out the possibilities of further technological improvement of the system performance. Valuable experiences for developing subsequent systems have been acquired through designing, constructing and testing the system.

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Experiments which simulated small break loss-of-coolant accidents (SBLOCAs) resulting from 2.10.13% break in the cold leg of a PWR were conducted with an apparatus of 1/270 scale in volume. In the large break size case, the decay heat was mainly removed by the break flow and in the case of a small break, the steam generator played an important role. In this case, thermal hydraulic behaviors such as natural circulation and reflux condensation cooling were important during the transient. Depressurization in the secondary system due to bleeding steam from the steam generator by an operator action was so effective to make the accident to come to an end. The operation to depressurize the secondary system was also efficient to rewet the core which had been uncovered due to a loop seal formation in a cross-over leg.
No effects of initial 200 ppm dissolved gas in the coolant were observed on the cooling performance of the steam generator. It was considered that it was because the gas which came from the coolant into the steam during the depressurization transient did not remain in the tubes of the steam generator.

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The coated particle fuel has been developed within a framework of the HTTR (High Temperature engineering Test Reactor) Development Program at the Japan Atomic Energy Research Institute. The HTTR fuel is a prismatic block type containing TRISO-coated UO₂ particles. Research and development on the fuel has been progressed in three categories ; a work for fuel production technology, a proof test of fuel performance and a safety-related research. In the present report the concept and outline of the fuel in the HTTR design are firstly described, and then fuel fabrication technology including recently developed methods for improving fuel quality is followed. Tests for proving fuel performance have been carried out extensively on the reference fuel of the HTTR design by irradiation in an in-pile gas loop and capsules, and typical results are presented in this report. Concerning the safety-related research, fuel failure and ¹³⁷Cs release at abnormally high temperature are described.

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