With the recent development of nuclear energy in large-scale, the problem of the exposure of the public has become to be regarded as of major importance nowadays. In spite of all the possible efforts of safety operation of nuclear facilities, there may be still a potential hazard of the exposure of human beings to small doses of ionizing radiations over prolonged periods of time. The biological evaluation of risks from radiation must be made on the basis of the dose-effect relationship, but the difficulties of obtaining such a relationship at low dose and dose-rate are due mainly to the extremely low frequency with which effects might occur. Therefore, the estimates of the incidence of the effects at low levels in man have been found on the extrapolation to low level of a few available data observed at relatively high dose and dose-rate. The validity of such an approach is influenced many unknown and undefinite factors. The present paper will give a general outline of the problems concerning the risk evaluation of radiation hazards, centred on BEIR report published in 1972.
The radioactive waste incinerator at Tokai Research Establishment, JAERI was installed in 1966, and has been operated routinely for seven years. In the operation, a lot of inadequate parts of the incinerator such as furnace, spray scrubber, cyclone, and electrostatic precipitator have been improved. This experimental program was carried out to examine the decontaminability of furnace and exhaust-gas system. The decontamination factors (DF) of the incinerator components were determined by obtaining the ratio of activity of 32P in the influent gas to that in the effluent gas. DF of 3.6×10 in the spray scrubber and 7.0×10 in the electrostatic precipitator were obtained. Retention factor in the furnace was 2.3×10. Using the value of 1.0×102 in the cloth filter and 1.0×103 in the HEPA filter obtained in the previous examination (in 1966), the over-all DF of the incinerator was calculated to be 6×109. Also the distribution of radioactive material in each part of incinerator was 93% in the ash, 5% in the spray scrub solution, 0.5% in the electostatic precipitator, 0.02% in the cloth filter and 0.3% in the duct of exhaust-gas.
For the land storage of solidified radioactive wastes with cement, their volume must be minimized with keeping a sufficient strength. Generally, the material strength and the volume of a solidified waste are dependent on the composition of mixed waste, cement and water, however, their relationships have not been investigated yet. In this report, Volume Factor (V. F.) was defined as the volumetric increase of solidified waste, and the value of V. F. and the strengh were determined experimentally for the various compositions of radioactive wastes, cement and water. The experimental results were illustrated graphically for the handy use of practical estimations of V. F. and the strength of solidified radioactive wastes with cement.
The consumption of leaf vegetables was surveyed on three kinds of families in Kuji town and Tokai village. The average daily intake through a year was 116, 115 and 132g/d/p for fisherman's families in Kuji, native's in Tokai and immigrant's from city to Tokai village, respectively. High consumption of leaf vegetables was observed in autumn and winter, and less consumption in summer. All the year round the cabbage and welsh onion were consumed, in summer the lettuce and from autumn to spring the chinese cabbage and spinach. The average daily intake of each leaf vegetable was calculated. Dimensions of the leaves of leaf vegetables relating to the deposition of gaseous iodine-131 were also measured.
The consumption of fruit vegetables, flower vegetables and mushrooms was surveyed on three kinds of families in Kuji town and Tokai village. Very high consumption was observed in summer contrasting with the case of leaf vegetables. The average daily intake of those through a year was 68, 98 and 65g/d/p for fisherman's families in Kuji, native's and immigrant's in Tokai, respectively. Nearly all the year round the cucumber was consumed much, followed by the beans sprouts and sweet pepper though less consumption, in summer the eggplant and tomato, and from autumn to winter the cauliflower. It was also recognized that the consumption frequency of fresh “Shiitake” was considerably high though the consumption rate was not so high.
Radioactive aerosol particle is thought to be very useful for experimental works on aerosol technology. However, for the practical use of radioactive aerosols, the production method must be carefully selected from the view point of safety in the operation as well as the fittness for use. This article is a review on various methods which have been utilized in various fields of research and test.