In response to the recent structural imbalance of oil supply and demand, Japan has placed energy security at the top agenda of its energy policies. A review of the energy security level has importance in formulating and steering energy policies. Although energy security meant national energy security that puts the main priority on a stable energy supply, we are now required to consider energy security from wider viewpoints of global energy security, which includes environment, nuclear concerns, international relations and others as its priority aspects. This report is prepared to suggest a method of estimating energy security level in a quantitative manner. In this method, Japan's energy supply and demand structure is evaluated on the selected aspects and indexes as standard deviation among eight advanced nations and one area. The aspects and indexes include energy consumption, environment and economics as well as energy supply. The outcomes prepared by this method show that Japan is now placed at a lower position than most advanced nations and area, although its energy security level has been improved mainly with the contribution of the diversification of energy supply sources. The estimation also shows that Japan's energy security could improve until the portion of nuclear energy in the power supply reaches around 60% on the assumption of its present energy supply and demand structure. The future task is to determine the aspects and indexes to be picked up or the possible weight to be distributed among the aspects and indexes in response to the situations surrounding energy.
Clearance is one of the useful concepts to manage large amounts of slightly contaminated solid radioactive materials generated from the decommissioning of nuclear facilities. Cleared materials are expected to be disposed of as conventional wastes or recycled to produce consumer goods. In Japan, the legal framework for clearance was established in 2005 by amending the Law to regulate nuclear materials, reactors and so on. However, it is not so clear whether the general public understands clearance well. In this paper, major concerns about clearance from the general public are analyzed based on the public comments for reports on clearance prepared by the Nuclear Safety Commission and the Nuclear Institute Safety Agency. The major anxieties for clearance expressed by the general public are the safety of clearance, unknown factors of radiation effects, possibilities of excess radiation exposure due to inadequate measurements of radioactivities and fairness in decision making. In order to deal with those anxieties, some countermeasures including the confidence in nuclear operators and regulatory authorities and controllability of clearance by the general public are discussed to promote the social acceptance of clearance by the general public.
Although dwellers living near a nuclear power station are entitled to economic/financial benefits such as increased job opportunities and local tax revenues pertaining to the power station, it is not clear whether such benefits are appreciated by the dwellers. Two findings of this study based upon a social survey of local dwellers living near the Kashiwazaki-Kariwa Nuclear Power Station are summarized as follows. First, an increase in the per capita sizes of the local tax revenue and national subsidies resulted in a larger share of respondents who thought that those revenues are beneficial. Therefore, local dwellers are aware of the sizes of economic/financial benefits. Second, given the same risk level of nuclear disaster, a larger per capita financial benefit resulted in a larger share of respondents who felt compensated for the nuclear risk. However, this increase in the number of compensated respondents is low relative to the increase in the amount of financial benefits.
Siting of radioactive waste management facilities frequently raise arguments among stakeholders such as a municipal government and the residents. Risk communication is one of the useful methods of promoting mutual understanding on related risks among stakeholders. In Finland and Sweden, siting selection procedures of repositories for spent nuclear fuels have been carried out successfully with risk communication. The success reasons are analyzed based on the interviews with those who belong to the regulatory authorities and nuclear industries in both countries. Also, in this paper, risk communication among the Japan Radioisotope Association (JRIA), a local government and the general public, which was carried out during the establishment process of additional radioactive waste treatment facilities in Takizawa Village, Iwate Prefecture, is analyzed based on articles in newspapers and interviews with persons concerned. The analysis results showed that good risk communication was not carried out because of the lack of confidence on the JRIA, decision making rules, enough communication chances and econmic benefits. In order to make good use of these experiences for the future establishment of radioactive waste management facilities, the lessons learned from these cases are summarized and proposals for good risk communication (establishment of exploratory committee and technical support system for decision making, and measurements to increase familiarity of radioactive waste) are discussed.
The adverse events which occurred in nuclear power plants are analyzed to prevent similar events, and in the analysis of each event, the cause of the event is classified by a cause classification method. This paper shows a new cause classification method which is improved in several points as follows: (1) the whole causes are systematically classified into three major categories such as machine system, operation system and plant outside causes, (2) the causes of the operation system are classified into several management errors normally performed in a nuclear power plant, (3) the content of ageing is defined in detail for their further analysis, (4) human errors are divided and defined by the error stage, (5) human errors can be related to background factors, and so on. This new method is applied to the adverse events which occurred in domestic and overseas nuclear power plants in 2005. From these results, it is clarified that operation system errors account for about 60% of the whole causes, of which approximately 60% are maintenance errors, about 40% are worker's human errors, and that the prevention of maintenance errors, especially worker's human errors is crucial.
An action research project called dialogue forum has been conducted in this study. The essential constituent of the project is a series of repetitive dialogue sessions carried out by lay citizens, nuclear experts, and a facilitator. One important feature of the project is that the study has been conducted based on the qualitative research methodology. The changes in opinions and attitude of the dialogue participants have been analyzed by an ethno-methodological approach. The observations are summarized as follows. The opinions of the citizen participants showed a significant shift from emotional to practical representations along with the progression of the dialogue sessions. Meanwhile, their attitude showed a marked tendency from problem-statement-oriented to problem-solving-oriented representation. On the other hand, the statements of the expert participants showed a significant shift from expert-based to citizen-based risk recognition and description, and their attitude showed a clear tendency from teaching-oriented to colearning-oriented thinking. These changes of opinions and attitude have been interpreted as a coevolving rather than a single process. It can be stressed that this type of change is most important for the reestablishment of mutual trust between the citizens and the nuclear experts. In this regard “The Process Model of Coevolution of Risk Recognition” has been proposed as a guideline for developing a new scheme of public communication concerning nuclear technology. The proposed process model of coevolution of risk recognition is regarded to be essential for appropriate relationship management between nuclear technology and society in the near future.
This paper discusses a rational methodology to evaluate dose rate at the boundary of the interim storage facility using two methods; 1) a method taking into account “shade effect” which represents the self-shielding effect of interim storage containers, 2) utilization of a newly developed simplified code. It was proved that the method of the shade effect is applicable to the secondary gamma-ray, which dominates approximately 50% of the total effective dose rate. Thus, the effective dose rate attributed to the secondary gamma-ray depends on both the number of containers in the facility and the shade coefficient which represents the factor of the shade effect. Using this shade coefficient, the dose rate was estimated for the facility that stored 8 or 16 containers around the boundary of the facility and the results were consistent with that of the Monte Carlo calculation. In the present study, a simple neutron transport code, MCNP-ANISN_W, was newly developed aiming at the simplification of large-scale calculation. The results of the dose rate agreed well with that of the Monte Carlo calculation. The results of the present study show that the simple evaluation technique and the code developed in this study would be useful for the evaluation of dose rate around the boundary of the interim storage facility.
A one-step simple extraction chromatography method using a TODGA (N,N,N′,N′-tetraoctyl-diglycolamide) adsorbent column has been developed to separate the americium from plutonium-solvent extraction raffinate. The raffinate contained Am (~620 mg/l), Np (~107 mg/l), Ag (~2000 mg/l), Fe (~290 mg/l), Cr (~38 mg/l), Ni (~52 mg/l) and a trace amount of TBP. Small- scale and scale-up tests for the separation of americium and conversion to americium oxide were carried out in NUCEF. Efforts were made to increase the yield and purity of americium. The americium was separated with 83-92% yields and 97-98% purities by small-scale tests and 85-95% yields and 98-99% purities by scale-up tests. The yields for the conversion of americium nitrate solution to americium oxide were 89-100% by small-scale tests and 85-96 % by scale-up tests. Approximately 1.8 grams of americium oxide was recovered from 6 litres of the raffinate and supplied for the research on the high-temperature chemistry of TRU.
For the realization of dry reprocessing, an effective method for the decladding of spent oxide is necessary. We aim to develop a decladding process that integrates with dissolution using molybdate melt as the solvent. This melt possesses characteristics such as it can make actinide oxide such as uranium dioxide dissolve in a very short time without reacting with metal such as the cladding tube. It is necessary to clarify the chemical and electrochemical behaviors of uranium corresponding to the proposed process in this melt. In this study, gram-scale uranium experiments were carried out, and the reaction of the uranium in the melt was investigated. In Na2MoO4-Na2Mo2O7 melts under an inert gas atmosphere, uranium dioxide dissolves as Na4U(MoO4)4 without changing its oxidation valence. It was confirmed by XPS that the tetravalent uranium cation was oxidized by oxygen gas to hexavalent uranium cation in the melt. In the electrolysis process, it was clarified that no deposit was observed on a cathode at 750 degrees centigrade caused by the redissolution of the deposit. When the temperature of the melt was 700 degrees centigrade, the redissolution of the deposit was reduced. The granulated powder of UO2 was successsfully recovered on a cathode at 700 degrees centigrade.
The Tokai reprocessing plant (TRP) has thus far processed over 1,123 t of spent fuels from the beginning of its active operation in Sept. 1977. For the 30 years of operation of TRP, many technological problems have been overcome to obtain its stable and reliable operation. The process for the establishment of maintenance technology in TRP was evaluated through the analysis of significant plant equipment failures reported to the authorities concerned. Through these troubles and their solution, the following knowledge could be obtained. (1) Dimensional tolerance data were indispensable for the remote maintenance of mechanical parts. (2) Ensuring remote maintenance technology was necessary for the early restoration of stable operation from equipment failure. (3) Direct maintenance for equipment in the cell should be performed following preventive work planning under a strict safety organization and its rule. (4) Preparation of spare parts or spare cells was an effective approach for reducing difficulty in maintenance work caused by technical problems or cost. (5) To perform the checking of operability and maintainability, premeditated stopping of plant operation was effective for establishing stable operation. This knowledge of maintenance technology could contribute to the safe and stable operation of the Rokkasho reprocessing plant (RRP) and the design and construction of the next reprocessing plant.
There are no data available with regard to radon emanation coefficients for uranium-bearing wastes; such data are needed for the assessment of radiation exposure from radon that will be generated in the distant future as one uranium progeny at shallow land disposal sites for uranium-bearing wastes. There are many kinds of uranium-bearing wastes. However, it is not necessary to measure the radon emanation coefficients for all of them for two reasons. First, the radon emanation coefficients for uranium-bearing wastes contaminated by dissolved uranium are determined by the uranium chemical form, the manner of uranium deposition on the waste matrix, and the size of the particles which constitute the waste matrix. Therefore, only a few representative measurements are sufficient for such uranium-bearing wastes. Second, it is possible to make theoretical calculations of radon emanation coefficients for uranium-bearing wastes contaminated by UO2 particles before sintering. In the present study, simulated uranium-bearing wastes contaminated by dissolved uranium were prepared, their radon emanation coefficients were measured and radon emanation coefficients were calculated theoretically for uranium-bearing wastes contaminated by UO2 particles before sintering. The obtained radon emanation coefficients are distributed at higher values than those for ubiquitous soils and rocks in the natural environment. Therefore, it is not correct to just compare uranium concentrations among uranium-bearing wastes, ubiquitous soils and rocks in terms of radiation exposure. The radon emanation coefficients obtained in the present study have to be employed together with the uranium concentration in uranium-bearing wastes in order to achieve proper assessment of radiation exposure.