On March 30, 2007, Japan's electric utilities reported the results of a complete review of their power-generating units to the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade, and Industry (METI). The Ethics Committee of the Atomic Energy Society of Japan (AESJ) then recommended an assessment method to analyze the seriousness of the problems from multiple perspectives in order to support the public's understanding of the reported problems. Accordingly, the Ethics Committee conducted the assessment. The assessment considered each reported problem associated with nuclear power-generating units and the preventive measures completed between June 2007 and September 2008 (corrective measures continued beyond that period). The results were presented at the autumn conferences of AESJ in 2007 and 2008, and are discussed in this report.
Hydrogen is regarded as a clean fuel since it does not pollute when burned with air. The issue is how to produce substantial and inexpensive hydrogen for commercial use. The utilization of nuclear power to produce hydrogen from water has many merits. Firstly, nuclear power emits no carbon dioxide. Secondly, water contains hydrogen and exists everywhere. The HTTR-IS system is one of the plants producing hydrogen with nuclear power. Such a system has high safety requirements. One of the safety studies to be conducted is the probabilistic safety assessment (PSA) study for concerned hydrogen explosion, which was not studied previously. Therefore, this study is conducted for the preliminary PSA of flammable gas leakage in the HTTR-IS system. First, a master logic diagram (MLD) was developed to identify initiating events. After identifying initiating events, event tree analysis (ETA) and fault tree analysis (FTA) were performed to quantify the average frequency of an accident. The initial result of the PSA shows that the nominal frequency of explosion is 2.5×10−4 1/y. This frequency is higher than the criterion defined in this paper and unacceptable. Installments of additional components are investigated in order to reduce frequency. As a result, the average frequency of explosion is decreased to 7.9×10−7 1/y.
In France, there exist organizations called “Commission Locale d'Information” (CLI) in all the siting areas where nuclear facilities located. Previously, the CLI organizations were established voluntarily by some local governments or nuclear utilities. Since 2006, however, the Nuclear Transparency and Safety Act has obliged the establishment of CLI in all the siting areas in conjunction with reforming the nuclear regulatory agencies. This means that the concerned local governments are officially part of nuclear safety regulation. In this study, we investigated present conditions of the CLI organizations through some interviews in France and consider their roles from the standpoint of nuclear regulatory governance. As a result, we found that the CLI plays the following roles: (1) medium of communication among concerned parties (not only between nuclear utilities and local habitants but also between the national nuclear regulatory agency and various local governments) and (2) implementing various activities in accordance with each local condition through the participation of local assembly members. In addition, we clarified that CLI's activities are supported by related institutional infrastructures, such as cost burden between central and local governments, and some other systems of citizen participation in building or expanding nuclear facilities.
A conventional training program for nuclear power plant operators has been developed with emphasis on improvement of knowledge and skills of individual operators. Although it has certainly contributed to safety operation of nuclear power plants, some recent incidents have indicated the necessity of an improved training program aiming at improvement of the performance of operators working as a team. In the aviation area, crew resource management (CRM) training has shown the effect of resolving team management issues of flight crews, aircraft maintenance crews, and so on. In the present research, we attempted to introduce the CRM concept into operator training in nuclear power plants as training for conceptual skill enhancement. In this paper, a training method specially customized for nuclear power plant operators based on CRM is proposed. The proposed method has been practically utilized in the management training course of Japan Nuclear Technology Institute. The validity of the proposed method has been evaluated by means of a questionnaire survey.
Caesium (Cs) is one of the known fission products (FPs) in spent fuel arising from nuclear electric power generation, which remains in the medium of pyroreprocessing after prolonged operation. We greatly hope to develop a new functional material that would make it possible to remove FPs, such as Cs, for regeneration of the medium. Iron phosphate glass could be used to immobilize high-level radioactive waste (HLW) and could function as a Cs sorpant. However, it must endure high temperatures from about 350°C, the melting point of LiCl-KCl electrolyte, to 600°C, the operational maximum temperature. In this study, we have successfully developed the iron phosphate glasses functioning as Cs sorpants and exhibiting heat resistance. To prevent glass softening at temperatures around 600°C, alkali metal oxides, alkaline-earth metal oxides, alumina, and titania were added into the Fe2O3-P2O5 glass. Through soak experiments of the glasses in molten salt (3LiCl-2KCl) containing CsCl, it was found that the glasses immobilized Cs by reacting with CsCl and formed the crystal phase of CsFeCl3 and/or Cs3FeCl6. This Cs sorption function is peculiar to the developed iron phosphate glasses.
Elemental data for construction materials used in nuclear power plants are necessary for the prediction of radioactivity induced by neutron irradiation. To evaluate radioactivity in retired Japanese nuclear power plants, it is preferable to use elemental data of the structural materials actually used in each plant. However, since there is no such domestic database, NUREG elemental data are commonly used for this type of evaluation. It is, therefore, required to establish a domestic elemental database of the structural materials actually used in power plants. In order to obtain elemental data, more than 130 specimens were collected from the structural materials of the Fugen Nuclear Power Plant, which was constructed in the 1970s and whose operation was stopped in 2003. Seventy-six compositional elements in the specimens were analyzed using appropriate chemical analyses and measurement techniques, such as glow discharge mass spectroscopy and inductively coupled plasma mass spectroscopy. These obtained data were compared with NUREG elemental data and other standard or reference data. As a result, it was determined that the concentrations of major elements were not so different from NUREG elemental data and other standard or reference data. On the other hand, a slight difference was seen among the concentrations and their standard deviation in the analytical data of impurities, such as cobalt. These data are expected to become a reference in the establishment of domestic standard data, and they are also expected to be applied to the evaluation of irradiation-induced radioactivity in the structural materials of reactors that are subject to decommissioning in the future.