Public concern has increased about a variety of health risks, and many researchers are recognizing the importance of scientific risk analysis. However, the term “risk” includes various definitions, and it is not easy for us to have common recognition about risk. This paper presents a brief introduction to risk and risk assessment.
A thermal neutron reference field using a graphite pile of 190cm×190cm×250cm was developed at the High Energy Accelerator Research Organization. Inside the pile, the thermal neutron flux was measured by the gold foil activation technique using the Cadmium difference method, and outside the pile by the 3He proportional counter using the Cadmium difference method. Besides the gold foil, the optical fiber coupled to the ZnS(Ag) scintillator with the Li converter was used to measure the neutron flux inside the pile to verify its availability. The absolute values of thermal neutron fluxes measured inside the pile could be obtained with an accuracy of 7.5-7.8%. The measured thermal neutron fluxes inside the pile were compared with those calculated by use of the MCNP-4B Monte Carlo code. The calculated thermal neutron fluxes agreed very well with the measured ones. Outside the pile, the measured thermal neutron flux was 7.38×10-6 (n/[s·cm2·source neutron]), and the contribution of neutrons other than thermal neutrons was less than 1%. The thermal neutron fluxes measured by the optical fiber with the scintillator showed very good agreement with those measured with the gold foil activation method. The optical fiber detector was found to be quite useful to measure the thermal neutron flux distribution in the pile because of its much higher detection efficiency than that of gold foil activation.
The relevance of concepts brought to mind by stimulus terms concerning atomic energy and radiation utilization has been investigated to learn how people understand the present status of nuclear technology. The relevance of concepts was defined as the frequency distribution of words that came to mind immediately after seeing selected terms needed for present-day life as well as for nuclear engineering. An analysis of knowledge structure shows that (1) a concept of atomic energy has a close relation with that of electric power generation; (2) an understanding of nuclear power utilization may be promoted in relation to an understanding of energy and environmental problems because the concepts of energy, atomic energy, electric power generation, and natural environment have closer relations with one another; (3) a concept of radiation has various relations with harmful radiological health effects, but little relation with industrial, agricultural, and other beneficial uses except for nuclear power generation or medical applications. It also became clear from the investigation that studies on natural radiation may be important to promote an understanding of radiation utilization because a concept of the natural environment does not yet relate to that of natural radiation.
At the last amendment of the radiation protection law, dose limits were reduced. The natural radiation dose cannot then be negligible for radiation protection dosimetry at medical facilities. But because the natural radiation dose is not regulated, we should estimate it and subtract it from the measured gross dose. It is difficult to estimate a natural radiation dose precisely because it is affected by many factors. We examined the methods of evaluating a natural radiation dose when an integral dosimeter is applied to environmental radiation dosimetry in medical facilities. Because X-ray energy is low at most medical facilities and we ascertained that a filtered glass dosemeter can effectively separate X-rays and natural radiation. In this method, the total error is less than 30%, which is permissible for radiation protection dosimetry.
This survey on daily food intake in the northwestern part (northern Tsugaru area) of Aomori Prefecture was a continuation of a previous survey conducted in the southeastern part (Sanpachi-Kamikita area) and southwestern part (southern Tsugaru area) of the prefecture. The 50 families surveyed were divided into three different groups of primary occupations: fishery worker, farmer, and “other occupations.” The average total daily food consumption of the entire survey group was about 2, 389 gram/day/person (g/d/p), and showed no significant seasonal variation. The consumption rates of marine, agricultural, and livestock products were around 276, 1, 275 and 360g/d/p, respectively, and were relatively constant the year around. However, the consumption rate of other products was 478g/d/p and was slightly higher in the summer and lower in the winter. The proportions of marine, agricultural, and livestock products in total food consumption among all families were on the average approximately 12, 53, and 15%, respectively. The highest average daily food consumption recorded was 2, 510g/d/p and occurred in fishery workers' families, followed by 2, 441 and 2, 008g/d/p in farming and other workers' families, respectively. The families of fishery workers showed the highest consumption of marine products among all families. The consumption of agricultural and livestock products was remarkably high in farmers' families and low in other workers' families. The foods with the highest consumption rates in the northern Tsugaru area were: (a) squid, salmon, wakame, and cod among marine products, (b) rice, radish, apple, cucumber, tomato, and tofu (soybean curd) among agricultural products, and (c) milk, egg, and pork among livestock products. Some slight but statistically significant differences were recognized in the consumption patterns in the northern Tsugaru area in comparison with those of the Sanpachi-Kamikita area and the southern Tsugaru area.
The activities both long-lived fission products and transuranium elements depending on cooling time are discussed. Both glass and engineering barriers are not capable of safely sealing the long-lived fission products and especially transuranium elements after 500 years. Comparative analysis of different matrix materials is given. The results of relative costs for different nuclear waste management schemes for WWER-440 fuel reprocessing at RT-1 are presented.
The effects of a daily recommended human dose (1g per 70kg body weight=30μmol/kg) of calcium diethylentriaminepentaacetic acid (Ca-DTPA) on removal of plutonium from rats injected with different amounts of plutonium were examined. Sixty female wistar rats were preinjected with doses of 0.185, 0.37 and 3.7×105Bq/kg of plutonium as a nitrate, and half of the rats of each dose group were injected with 30μmol/kg of Ca-DTPA for 3 days, beginning 1h after plutonium injection on the first day. The 24-h urine and feces of rats were collected. The amount of urinary plutonium excretion in the Ca-DTPA groups was found to be significantly greater than that in the respective corresponding control groups at day 1-3. The amount of urinary plutonium excretion in the Ca-DTPA group at the 1st day was increased in response to the plutonium injected dose (correlation coefficient: r=0.628, vs. r=0.573 in the control group), that accumulated in the Ca-DTPA group for 3 days was r=0.800 vs. r=0.669 in the control group), while their rates of plutonium injected dose were decreased. Such findings were not obtained in the feces measurements. In conclusion, a human dose of Ca-DTPA chelation therapy enhances plutonium excretion as increasing plutonium intake, however the excreted rate of plutonium intake is decreased.