This paper discusses issues related to the national consensus on nuclear energy policy between the public and the government. Firstly, the public objections on energy issues were analyzed by reviewing recent national policy documents, public opinion polls and comments on the nuclear energy policy. From the analysed results, it was confirmed that the government asks the public for acceptance and cooperation of the national policy; meanwhile, the public pursue to satisfy their appetite and make their own choice in their daily life without awareness of energy itself. As a consequence, the difference of standpoints between the two parts was assumed to interfere with effective communication especially regarding nuclear energy issues. Based on these considerations, essential conditions relevant to the national consensus for better mutual understanding are presented. It is also newly proposed that energy communicator should be independently established to assist the desirable dialogue between them. Finally, fundamental concept, roles and requirements for the communicator are pointed out from the viewpoint of implementation of the practical dialogue.
Alpha-ray spectrometry for a plane thick sample in which radioactivity is homogeneously distributed was applied to the determination of alpha-emitting radioisotopes without chemical separation processes. A homogenous glass sample containing alpha-emitting radioisotopes could be prepared by borax bead reaction. An alpha-ray spectrum of the glass sample containing 228Th indicated that release of 220Rn from the sample, which causes contamination of a detector surface with daughter nuclides of 220Rn, was almost negligible. Concentrations of alpha-emitting radioisotopes of Th series in the glass sample were determined quantitatively from the alpha-ray spectrum and stopping power of the medium calculated from its chemical composition. In the glass sample made from borax and spent fuel solution, radioactivity concentration of 244Cm, 238Pu+241Am, and total alpha were comparatively consistent with those obtained by the precision method of radiochemical analysis.
The radon emanation fraction E is a very important parameter for safety assessment of uranium bearing waste. However, reported E values have been measured only for natural material or uranium ore. This paper describes the development of a measurement method of E for uranium bearing waste, and presents measured E values for calcium super phosphate. Measured E values were dependent on moisture saturation M and the maximum E was measured when M was about 0.2. The E values for the calcinated material were low, 1/4 to 1/6 of those for the raw material. Each E value was estimated by two methods: using Eg which was based on a difference of gamma ray counts, and using Ea which was based on alpha-ray count. Almost all the Eg values were in good agreement with the Ea values.
Leakage of solution was found to occur from a steam jet in an acid recovery process at the Tokai reprocessing plant. To determine the cause, we retrieved the steam jet unit from the cell which held it and examined the inside. As a result, it was revealed that a corrosion defect had penetrated the inside of the structure, originating from the steam nozzle root in the suction part of the jet unit. To ascertain why such a failure occurred, we carried out observation of the metallurgical structure of the jet unit, an analysis of the temperature distribution of the structure involving verification with a trial jet unit, and a corrosion test of the material. Consequently, the origin of the corrosion defect was determined to be a pin hole on the material surface at the end of the steam nozzle root, where nitric acid fluid had been in contact, and the defect progressed along the structure at a temperature of about 120°C. Anisotropy of the material, possibly originating in the manufacturing process, was observed from the corrosion test. As a result of these investigations, we have devised a new design to improve the corrosion resistance.
A number of consumer's goods which contain natural uranium and thorium are circulated in the familiar living environment. Based on various kinds of information sources, 20 kinds of these consumer's goods were collected and their radioactive concentrations were measured by using ICP-MS and Ge semiconductor detector. As this result, it was found that the concentrations of uranium and thorium in the consumer's goods used at home and industries were below 34Bq/g and below 270Bq/g, respectively. Next, the concentrations of daughter nuclides were not so different from the ones of uranium or thorium, which showed that the secular radioactive equilibrium held between both concentrations. In addition, the radiation exposures for public consumer were evaluated when four kinds of typical consumer's goods frequently used in daily life are utilized. The results computed by MCNP-4C code were below 250μSv/y.
In the fixed source problem such as a neutron deep penetration calculation with the Monte Carlo method, the application of the variance reduction method is most important for a high figure of merit (FOM) and the most reliable calculation. But, MCNP calculation inputs written in published literature are not to be best solution. The most concerned items are setting method for the lower weight bound on the weight window method and the exclusion radius for a point estimator. In those literatures, the lower weight bound is estimated by engineering judge or weight window generator in the MCNP. In the latter case, the lower weight bound is used with no turning process. Because of abnormal large lower weight bounds, many neutron are killed in no meaning by the Russian Roulette. The adjoint flux method for setting of lower weight bound should be adapted as a standard variance reduction method. The Monte Carlo calculation should be turned from the experience such as engineering judge to science such as adjoint method.