Technical knowledge and information on the geological disposal of radioactive waste should be readily understandable for stakeholders who make decisions on implementation of the disposal so that those would be effectively contributory to the decision-making process. To realise reasonable understanding and decisions on the radioactive waste disposal project, it is suggested to be effective and necessary that producing knowledge and information is carried out interactively with crystallizing variable requirements and concerns from stakeholders, rather than by giving technical information in only one direction even if it can be provided in detail. In this study, a communication methodology of knowledge management on radioactive waste disposal based on analysis of a series of dialogue experiments with citizens and a case study of discussion by political experts on the geological disposal project of high-level radioactive waste and TRU waste in Japan is discussed. It seems reasonable to conclude that there is a common process of stepwise understanding, in which stakeholders need general knowledge and information on the concerned issue in the first step and then obtain more specific knowledge to make decision in the later steps. In the knowledge management concept, it is suggested that the key issues are how to correct and arrange knowledge and information, not only technical ones but also political, economical and so on, by applying the methodology of interactive accumulation of them between stakeholders.
We developed a long-term continuous measurement method for in-situ gamma-ray measurement using a Ge semiconductor detector (in-situ Ge measurement), and performed continuous measurement for 36 months by the method. A measurement system was successfully stably operated for a long period, and it was confirmed that artificial radioactive nuclides were able to be detected at high sensitivity. A counting rate of each of 214Pb and 214Bi was increased about twice in correspondence to slight increase in environmental radiation dose rate of about 10% as a measurement value of a monitoring post using a NaI (Tl) detector. The problem of discriminating between natural radiation and radiation from man-made source was solved by this system.
Global 222Rn flux density distributions with a spatial resolution of 1° in latitude and longitude were estimated for each month in the period of 1979-2007 using an 222Rn exhalation model based on a porous media diffusion theory. This exhalation model calculated the 222Rn flux density as a function of the 226Ra content, soil water saturation, and soil temperature. The influence of the topographical ruggedness of the ground surface on the flux density was also considered in the model. The global average of the flux density during the 29-year period was estimated to be 21.3 mBq m-2 s-1. The annual variation in the globally averaged flux density showed a slight but steady increase since 1999. The seasonal variation in the globally averaged flux density was estimated to range from a minimum of 18.8 mBq m-2 s-1 in March to a maximum of 23.6 mBq m-2 s-1 in September. The regional averages for the annual flux density varied from 8.3 mBq m-2 s-1 for the northern part of North America to 33.5 mBq m-2 s-1 for Australia. The latitudinal distribution of zonally averaged flux density was found to be in good agreement with the latitudinal decline at high latitudes in the Northern Hemisphere. The spatial and temporal variations were caused mainly by variations in the soil water content and soil 226Ra content, but to a lesser extent by the soil temperature. The topographical ruggedness was found to increase the flux density by only 2% globally but by more than 10% in mountainous regions. Atmospheric transport simulations using the estimated flux density as input data showed that the simulated atmospheric 222Rn concentration was substantially lower than that measured at Hachijo Island, implying that the flux density of the present study with topographical ruggedness is still underestimated in the East Asian region.
The probability distribution of background cancer risk was examined using the detriment-adjusted risk defined by the International Commission on Radiological Protection (ICRP) on the basis of data on background cancer mortality in Japan. The purpose of this study is to gain information that is important in discussing the acceptability of radiation exposure in the low-dose region of 1 mSv/y or lower. The probability distribution was compared with the distribution of maximum assumed risk due to radiation from man-made radioactive nuclides calculated using the representative person concept defined by ICRP. The results revealed that the risk for members of the public is sufficiently small and lower than the risk that is within the deviation of the background cancer risk, if there is appropriate radiation protection compliance with the dose limit of 1 mSv/y.