Akira Nakaoka

Rapid determination method of radiocesium in sea water by cesium-selective resin

A rapid and precise method of determining radiocesium corresponding to 5 mrem/y, the Japan AECs guideline, was proposed. The development and practical performance of cesium-selective resin and the determination method was described in this paper. The resin was prepared by the formation of ammonium molybdophosphate in the structure of Amberlite XAD-7 resin. It took only 3 hours to carry out all the procedures the authors proposed. This value represents 1/10∼1/2 of the time of conventional method. The concentration of137Cs and134Cs in sea water was determined to be 0.13∼0.16 pCi/1 and less than 7.1·10−2 pCi/1, respectively.

Environmental effects of natural radionuclides from coal-fired power plants.

The assessment of the environmental effects of natural radionuclides contained in fly ash released from a coal-fired power plant was carried out and the following results were obtained. Mean concentrations of U, Th and K in 28 kinds of domestic and foreign coals were 1.0 ppm, 3.3 ppm and 2300 ppm, respectively. A good correlation between U and Th concentrations appears evident. Natural radionuclide concentrations of bottom and fly ashes were approximately equal in both ashes, and the values were the same as those calculated by concentration in coal divided by ash content. Release rates of 40K and radionuclides of each decay chain of U or Th were evaluated in the range of 2 to 40,000 pCi/sec for model coal-fired power plants of 1000 MW and 250 MW. The natural radionuclide concentration in air in a plume at the maximum concentration point was 5 X 10(-9) to 5 X 10(-3) pCi/m3, and these values were below 1/200 of those of natural origin.

Rapid pretreatment of environmental samples of food and related materials by a microwave dehydration method

A rapid and simple radioactivity determination method has been developed for food and related environmental samples of a radioactivity level corresponding to 5 mrem/y, Japan AECs guideline, by pretreating with a modified microwave dehydration apparatus followed by radiation counting. An equation to estimate the heating conditions by the apparatus has been derived, and results calculated by the equation are in good agreement with experimental data. It took less than 4.5 hours to dehydrate by the propossed method, and radiation counting could be started on the day of sampling and dehydration procedure. The lower limit of detection for each radionuclide by the proposed method, using a Ge(Li) detector of 20% relative efficiency, is lower than one half of the needed detection limit to determine and evaluate the 5 mrem/y level. Radionuclide levels in food samples such as vegetables and crustaceans were determined by the proposed method and it was found that they were below the lower dection limit of the proposed method except natural radionuclide40K and fallout-originated137Cs.

Correlation of environmental sample radioactivity determination with sample pretreatment.

Abstract This report describes a calculation equation for radioactivity determination, and sample pretreatment based on the fundamental design mentioned in previous report (Na79), which satisfied the guide for dose assessment objectives for a light-water-cooled nuclear power reactor (AECJ75). The effect of the sample pretreatment on the determination of half the level of needed determination limit (NDL} (Na79) was evaluated using a commercially available Ge(Li) detector system. It was clarified that pretreatment should be carried out for environmental samples up to 8301. of the initial sample amount. The most suitable radioactivity determination method with a commercially available Ge(Li) detector system far dose assessment is presented herein.

Generalization of radioiodine adsorption on geological materials

A generalized equation for adsorption of /sup 131/I/sub 2/ gas on geological material was used. Adsorption parameters for typical Japanese geological materials such as granite, tuff, and sandstone are evaluated as a function of temperature and surface area of rock material. Crushed sample investigations have been performed by the column technique at various steps of temperature and gas concentration. The results indicate that the isosteric differential heat of adsorption is in the range of 63 to 92 kJ/mol at 20/sup 0/C and that the adsorption coefficient depends on temperature and concentration. Water vapor in /sup 131/I/sub 2/ gas also affects the coefficient, which corresponds to the surface roughness of geological material. A generalized equation is derived on the basis of considering the size distribution of geological materials in order to evaluate the adsorption coefficients at various temperatures. By using this equation, the coefficients of intrafault materials in Japanese granite formations are evaluated at about 10/sup 3/ cm/sup 3//g.