Bulk cathodes with a large emission area are proposed for use in a magnetic multipole ion source of a neutral beam injector. Compared to designs with tungsten (W) filaments, this design simplifies the thermionic cathode replacement procedure. The cathode was tested by causing a hydrogen arc discharge in a rectangular shaped plasma generator (18 X 39 X 20 cm³). The generator had two La₂O₃ doped Mo (LM) cathodes of disk shape with 10 cm diameter, which were operated in the emission limited region to find the electron emission current density of LM as a function of its temperature. An arc efficiency of the generator estimated from the present data was 1/3 of that typically achieved in ion sources with the W filaments. In the experiment, a few improvements were also made for flattening the distributions of ion saturation current density near a plasma grid of generator and of the cathode temperature.

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The performance of main steam safety relief valve has been evaluated with respect only to the steam. In the present study, two-phase flow and subcooled water blow-out tests with model valves were performed in order to evaluate the valve's characteristics and per-formance. From the test results, it was made clear that not only for the steam but also for the two-phase flow the measurement data were hardly affected by scaling and also that the reaction force of the fluid to the valve stem was hardly dependent upon the void fraction. Analytical study was performed using the two-phase flow model in the valve. The results of the analysis showed good agreement with the test data. It was shown from the test and analysis results that the reaction force of the two-phase flow and subcooled water to the valve stem was almost as much as that of the steam flow, and the integrity of the safety relief valve could be maintained.

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Commercially available carbon fiber was used as a new resistive anode wire for a charge division type position sensitive proportional counter. It has a small diameter of 7 μm and a large electrical resistance of about 4 kΩ/cm and is available at a very low cost. Although about 3, 000 fibers are weakly sticked together in a bundle with a kind of adhesives, a single fiber can easily be taken out from the bundle after the dissolution of the adhesives by acetone. Because of the smaller diameter compared with conventional anode wires, the lower high voltage serves the purpose. However, in the same reason, the saturation of gas multiplication appeared and hence an energy linearity tended to be lost, which was not much trouble for position detectors. Electrical resistance was uniform throughout all the length, which resulted in a small standard deviation of ±0.35% in the position linearity for a length of 20 cm. The relative position resolution for collimated Mn KX-rays was 0.47% in FWHM.

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In order to determine the Counter-Current Flow Limitation (CCFL) in hot legs of PWRs, CCFL characteristics of air-water and saturated steam-water flow were experimentally investigated in a modeled flow path of a horizontal tube connected to an inclined riser. The ranges of dimensions of experimental tubes were as follows : diameter D 0.0260, 076 m, length of horizontal tube H 0.010.4 m, length of inclined riser I 0.0380.6 m and inclination angle of inclined riser θ 40°or 45°.
Wallis-type correlation (J_g^*1/2+mJ_l^*1/2=C) was applicable to the data during a steady separated flow. An analysis based on envelope theory showed that the constant C should be a function of H/D and I. A function of C with those parameters was empirically determined by using data obtained in this study. The developed function correlated well with the results of Richter el al. (D=0.203m, H=1.26 m, I=0.5 m and θ=45°). The constant m in the Wallis-type correlation was almost constant 0.75. The problems were discussed, which should be made clear to apply the correlation obtained in this study to an actual PWR hot leg.

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A system to diagnose abnormalities on structural materials in the primary cooling systems of BWR by analyzing water chemistry data is proposed. In the system, patterns composed of more than two kinds of water chemistry data are compared with several stages of reference patterns obtained by the models which relate the water quality changes to the structural material abnormalities. Small abnormalities on the materials canbe expected to be detected at very early stages and future abnormalities can be predicted by the diagnosis system.
In this paper, the basic structures of the anomaly detection system using water chemistry data are explained.

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Dry oxidation of spent ion exchange resin is one of the most effective methods to reduce radioactive waste volume and also to make the final waste form more stable. Thermogravimetric measurements were performed using cation exchange resins with or without Fe in either an ionized or unionized form to clarify the effect of metallic impurities on the resin oxidation.
The presence of an ionized Fe resulted in a considerable increase in the reaction rate constant, indicating that the Fe functioned as a catalyst. On the other hand, the unionized Fe showed no catalytic activity. Measurement of EPMA revealed that the ionized Fe was distributed uniformly throughout the resin particles, while the unionized one was distributed only on the surface of the resin particle.
Catalytic activity increased with ionized Fe concentration up to 0.5 mmol-Fe/g-dry resin, above which the activity tended to decrease. The X-ray diffraction study attributed this to Fe coagulation in the resin particle. Kinetic models for solid-gas reactions were also applied to the resin oxidation to evaluate catalytic activity quantitatively.

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Thin pellets of the LiF-PbF₂ system with no porosity were irradiated by thermal neutron. Then release experiment of tritium produced in the pellets was carried out at some constant temperatures. Thus diffusion coefficients of tritium in the LiF-PbF₂ system were estimated to obtain an activation energy of diffusion, which was found to be 0.51 eV at LiF mole fraction of 0.467. It was also observed that decrease of LiF concentration in the pellet brings increase of diffusion coefficient of tritium.

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A method of evaluating the effective energy of photon radiation by means of thermoluminescence dosimeters has been studied, that is based on the property of thermoluminescence phosphors to change their ratio of responses between measurements made behind two different filters according to the effective energy of radiation. With this "pair filter" method, the effective energy can be evaluated in a wide range of energies by changing the combination of materials and thicknesses of the filter pair. Compared with the phosphor method, the pair filter method will appreciably reduce the coefficient of variation representing the degree of scattering shown by the evaluated effective energy of photon radiation. It is considered that the pair filter TLD method should serve practically in evaluating the effective energy of radiation and the resulting exposure.

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GAMMA R is a preliminary design study of a Tandem Mirror fusion power reactor of 3, 500 MW. The ratio of the central cell magnetic field to the choke coil magnetic field has a serious influence on the plasma Q. It is desirable to construct a high field choke coil. As a first step, a superconducting magnetic coil with 20 T central field is examined from the view point of the structural analysis.
The stress and the deformation induced by the magnetic force are studied by the finite element code SAP 4. As structural steel, the JAERI target material may be used, which has the yield stress of 1, 200 MPa and the fracture toughness of 200 MPa√m at 4K. It is shown that the maximum stress in the structural component is about 500 MPa and the maximum strain in the superconducting material is 0.3%. The possibility of the realization of a 24 T choke coil is also investigated. But it appears much difficult unless the plasma radius could be reduced to an appropriate value.

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The purpose of the present work is to investigate the Doppler effect and the self-shielding effect of resonances in the unresolved energy region of Nb. The effective average total cross sections (abbreviated EATCS hereinafter) of Nb were measured by using filtered neutron beam of 24, 54 and 144 keV as a function of sample thickness at room temperature for the self-shielding experiments. The measurement for the Doppler broadening effect has also been made at 600°C by using the 24-keV neutrons to observe any sensitivity of the Doppler effect with respect to the temperature. The methods have been reported for U and Sn by Tsang et al.⁽¹⁾ and for Th by Kobayashi et al.⁽²⁾ and Fujita et al.⁽³⁾ We have also compared the experimental results with the results calculated by the U3R code⁽⁴⁾ by using the JENDL-2 file⁽⁵⁾.

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The Purex process in mixer-settlers⁽¹⁾⁽³⁾ has been modelled and simulated by the non-equilibrium extraction model that employs a defined Murphree stage efficiency⁽⁴⁾ as the fitting parameter for simulation. However, Murphree stage efficiency can not be applied as it is to the chemical reaction system of the Purex process, because Murphree stage efficiency is defined for the mass distribution of non-chemical reaction system.
In the present study, a partial equilibrium model was presented that expresses an effective mass distribution between aqueous and organic phases for chemical reaction system with a new stage efficiency ; a complete mixing fraction. And the significance of the new stage efficiency was examined comparing with Murphree stage efficiency.

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In molecular laser isotope separation of uranium (MLIS), the compound UF₆ is a natural choice since it is the most familiar material in conventional uranium enrichment processes. The UF₆ has the sufficient chemical stability and the highest vapor pressure of all known uranium compounds. However, the studies on MLIS have not been as successful as those on AVLIS (atomic vapor laser isotope separation) until recently owing to the lack of the suitable infrared lasers that can be tuned precisely to the absorption center of the ²³⁵UF₆ν₃ band near 16 pm.
Many attempts have been made to develop the 16 μm lasers. Continuously tunable 16 μm radiation was obtained using an optical parametric oscillator⁽¹⁾⁽²⁾. Since the available energy was very small, however, the second laser for dissociation of the vibrationally excited UF₆ was needed. The groups at Los Alamos National Laboratory and Centre d'Etudes Nucleaires at Saclay both utilized the UV laser for this purpose. But it was found⁽³⁾⁽⁴⁾ that the use of the UV laser deteriorates the isotopic selectivity because even unexcited UF₆ absorbs the UV laser very strongly. Although infrared multiphoton excitation without using UV lasers was expected to yield better selectivity, no high-power gas laser had the capability of tuning the laser frequency to the center of the ²³⁵UF₆ 16 μm band until the advent of the p-H₂ Raman laser. For example, the CO₂-pumped CF₄ laser was found to be successful in dissociating UF₆ only in the region between 610 and 620 cm^-1(5), which corresponds to the lower frequency tail of the absorption of ²³⁸UF₆.
Immediately after the proposal⁽⁶⁾ and the following successful demonstration⁽⁷⁾, it was recognized that p-H₂ Raman laser is the most suitable 16 μm laser which is capable to tune over the region of ²³⁵UF₆ absorption. It is a scalable gas laser based on well established CO₂ laser technology and on the very efficient stimulated rotational Raman scattering conversion in a gaseous medium.
Using this p-H₂ Raman laser, Rabinowitz et al.⁽⁸⁾ demonstrated infrared two-color multiphoton excitation to dissociate UF₆ selectively at ambient temperature. Although their choice of all-infrared excitation scheme itself is more advantageous than IR-UV excitation scheme, the selectivity was not very high probably owing to the fact that UF₆ was not cooled with an expansion nozzle. They reported a selectivity of 1.20. Since the amount of UF₆ treated in their experiment was small, they developed a complicated on-line detection system for the isotopic selectivity measurement.
It is always of great interest from a practical viewpoint whether the selectivity observed at the time immediately after dissociation is deteriorated by the secondary reactions or not. In this note, an attempt was made to irradiate UF₆ contained in a static gas cell with one-frequency p-H₂ Raman laser and to obtain the selectivity based on the stable compound remaining in the cell after irradiation.

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