加速器屏蔽体中氚的提取和比活度测量

使用红外炉发展了一种从活化混凝土中提取氚的方法。通过研究氚的提取效率与加热温度、加热时间的关系,获得了氚的提取优化条件为在800℃下加热30min,Ar气流量设置为200mL/min。氚由两个冷凝管收集,然后装到1个小玻璃瓶中,与液体闪烁体混合,使用液体闪烁计数器计数。使用这种方法提取氚只需55min。相对于使用电子炉提取氚的方法,氚的提取效率可达到100%。收集了两个加速器屏蔽体中的混凝土样品,测量了样品中的γ射线核素和氚的放射性比活度。结果显示,氚的比活度与¹⁵²Eu和⁶⁰Co的比活度有很强的相关性。可得出结论：氚主要产生于热中子俘获反应⁶Li(n,α)³H。因而,可使用⁶⁰Co的放射性比活度简单估计活化的混凝土样品中氚的放射性比活度。     

Tritium Isotope Separation by CO2 Laser Irradiation at Dry Ice Temperature

A computational method based on boundary element method (BEM) has been developed to analyze transient temperature distribution in a three-dimensional solid having non-linear boundary condition (for example boiling or thermal radiation). To obtain high numerical accuracy, the heat transfer coefficient which depends on the surface temperature was approximated as a linear combination of interpolation functions with respect to time and analytical time integration of the non-linear term included in boundary integral equation was made.

To investigate feasibility of the present method, it was applied to calculations of the temperature distribution in an infinite flat plate cooled on one side. The heat transfer co-efficient of cooling surface was in proportion to n-th power of the surface temperature. Results are (1) the method has given a stable solution for non-linear boundary value problems such as conventional BEM could not solve, (2) it has given an accurate solution for large time increment except for first time step, and (3) an optimal relaxation factor decreases with strength of non-linearity of the heat transfer coefficient.

Applying the method to thermal analysis of limiter and divertor plate installed in a fusion test facility and fusion reactor respectively, availability of the method has been confirmed.     

Attachment of Membrane Separator for Removal of Radon to Ionization Chamber Installed for Tritium Stack Monitor

The effect of background counts induced by α-particles mainly from Rn in air was removed by the attachment of a water-permselective membrane separator to a tritium stack monitor equipped previously. Water vapor, after permeating the membrane selectively, was carried by N₂ gas into an ionization chamber where the activity of tritium was measured. The consumption of N₂ gas for carrier was reduced by recycling the gas through dehumidification processes; (1) condensation by pressure, (2) condensation by refrigeration and (3) adsorption (by adsorbents), so that there is no added daily work arising from the attachment for maintenance of the tritium monitor.     

Pressure Balanced Type Membrane Covered Polarographic Oxygen Detector for Use in High Temperature-High Pressure Water

Component analysis of gamma-ray doses in criticality accident situations is indispensable for further understanding on emission behavior of gamma-rays and accurate evaluation of external exposure to human bodies. Such dose components were evaluated, categorizing gamma-rays into four components: prompt, delayed, pseudo components in the period of criticality, and a residual component in the period after the termination of criticality. This evaluation was performed by the combination of dosimetry experiments at the TRACY facility using a thermoluminescent dosimeter (TLD) made of lithium tetra borate and computational analyses using a Monte Carlo code. The evaluation confirmed that the dose proportions of the above components varied with the distance from the TRACY core tank. This variation was due to the difference in attenuation of the individual components with the distance from the core tank. The evaluated dose proportions quantitatively clarified the contribution of the pseudo and the residual components to be excluded for accurate evaluation of gamma-ray exposure. Such the contribution sum increased with increase in the distance from the core tank and was estimated to be in the range of 16 to 40% of the total gamma-ray dose measured by the TLD at TRACY.     

Numerical Calculation of H2-HT Separative Performances up to −0.3 MPa of Thermal Diffusion Column with Fairly Higher Hot-Wire Temperature

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H₂-HT separative performances of thermal diffusion column with 15 mm-radius and 288.15K cold-wall was analyzed up to ?0.3 MPa for higher hot-wire temperature (up to ?1,700K). Flow analysis has revealed: (1) The magnitude of the free convection is almost proportional to the pressure, and laminar solution of free convection could not be obtained at the pressure more than ?0.32 MPa. (2) The magnitude of the free convection increases gradually with ΔT (the temperature difference between hot and cold surfaces), when ΔT<–800 K. In the range of larger ΔT, the magnitude is almost constant or rather decreases gradually with ΔT. As a result, the laminar solution could always be obtained at the pressure less than ?0.32 MPa, no matter how large ΔT may be. Separative analysis for H₂-HT isotope separation has made clear that the thermal diffusion column with 288.15 K cold-wall should be operated at (1) 0.15–0.2 MPa, (2) ΔT that is as large as technically possible, and (3) the feed rate F of 50–100 cm³ (288.15 K, 0.1 MPa)/min.     

Effects of Radiation on Gas Permselective Membranes

A study was performed on the effect produced by radiation on the gas permeation and gas separation performances of cellulose acetate and silicone rubber membranes, to be used in gas separation cells. When cellulose acetate membranes are irradiated, the resulting temperature rise causes a reduction in the gas permeability and improves the gas separation factor. By producing an approximately equal decrease in gas permeability, a dose rate of 2.0×10⁵ rad/sec was found equivalent to annealing at 140°C, which is in substantial agreement with the membrane surface temperature measured during irradiation. The results obtained with silicone rubber membrane were similar to those reported by Robb and Nakagawa.