On March 11, 2011, the Tohoku District-off the Pacific Ocean Earthquake and the subsequent tsunami resulted in the severe core damage at TEPCO's Fukushima Dai-ichi Nuclear Power Station Units 1-3, involving hydrogen explosions at Units 1, 3, and 4 and the large release of radioactive materials to the environment. Four independent committees were established by the Japanese government, the Diet of Japan, the Rebuild Japan Initiative Foundation, and TEPCO to investigate the accident and published their respective reports. Also, the Nuclear and Industrial Safety Agency carried out an analysis of accident causes to obtain the lessons learned from the accident and made its report public. This article reviews the reports and clarifies the differences in their positions, from the technological point of view, focusing on the accident progression and causes. Moreover, the undiscussed issues are identified to provide insights useful for the near-term regulatory activities including accident investigation by the Nuclear Regulation Authority.
In the light of the Fukushima Daiichi nuclear power plant accident, we need to consider a symbiosis method based on the diminution of the nuclear power industry. To find a region that does not excessively depend on the nuclear power industry, it is necessary to examine and discuss the social impact of nuclear-related industries. In this study, we compared people's changing information needs of social impact before and after the Fukushima Daiichi nuclear power plant accident. It was found that the need for information increased after the accident. In particular, there were three research areas where the need for information increased: the consideration of building nuclear power plants, the influence of harmful rumors on the region, and influence on the nuclear power industry. Next, attempts were made to understand whether there is a difference between information needs of social impact by attributes, such as age, sex and knowledge of nuclear power. The information needs of the following categories of people increased after the accident: people aged between 10 and 50 years, women, people who do not have a clear opinion about the use of a nuclear power plant, and people who do not have any knowledge of nuclear power.
The French history of nuclear development clearly shows the inseparability of its civilian use from military use. In France, Commissariat à l'Énergie Atomique (CEA) and Électricité de France (EDF) have played an important role in research and development of nuclear technology since the postwar period. At first, the two organizations had kept great autonomy, but the government reinforced its control on them because France needed nuclear deterrence against the Soviet Union. France began using plutonium in 1952, and the Suez crisis in 1956 showed the need for nuclear force to ensure its independence. After this event, France managed the first nuclear test using plutonium in 1960. As for enriched uranium, they have long had great difficulty in securing it. The uranium enrichment technology became crucial also in civilian use in this period. EDF proposed the pressurized water reactor (PWR), which requires enriched uranium, as the future reactor type because of its economic advantage, but CEA wanted to continue developing the gas-cooled reactor (GCR) because of its independence in nuclear fuel supply. Finally, they chose PWR because a French enrichment facility was built in 1967. From such French history, we can say that the civilian and military use of nuclear technology are inseparable.
During steady-state irradiation of metallic fuel in fast reactors, rare-earth fission products can react with stainless steel cladding at the fuel-cladding interface. The authors conducted isothermal annealing tests with some diffusion couples to investigate the structure of the wastage layer formed at the interface. Candidate cladding alloys, ferritic-martensitic steel (PNC-FMS) and oxide-dispersion-strengthened (ODS) steel were assembled with rare-earth alloys, RE5 : La-Ce-Pr-Nd-Sm, which simulate the fission yield of rare-earth fission products. The diffusion couples were isothermally annealed in the temperature range of 500-650°C for up to 170 h. In both RE5/ODS-steel and RE5/PNC-FMS couples, the wastage layer of the two-phase region of the (Fe, Cr)17RE2 matrix phase with the precipitation of the (Fe, RE, Cr) phase was formed. The structure was similar to that formed in RE5/Fe-12Cr and RE5/HT9 couples, which implies that the reaction between REs and steel is not significantly influenced by the minor alloying elements within the candidate cladding materials. It was also clarified that the increase in the wastage layer thickness was diffusion-controlled. The temperature dependence of the reaction rate constants were formulated, which can be the basis for the quantification of the wastage layer growth.
To evaluate the dissolution rate of radionuclides from hull waste under geological disposal conditions, corrosion tests using a coupon type of Zircaloy-4 specimen were conducted in deoxidized deionized water at 80, 100 and 120°C by a hydrogen gas generation rate method. The corroded depth of Zircaloy was proportional to the cubic root of corrosion time at each temperature. The corrosion rate constants obtained in the present study fell on the same line on the Arrhenius plot as those at a higher temperature of around 300°C that had been obtained in material research for light water reactors. These results indicate that the corrosion mechanism of Zircaloy at 80-120°C is the same as that at the higher temperature and that an empirical corrosion rate model at the higher temperature may be applicable to a temperature below 100°C that is likely under geological disposal conditions.
The development of an accident consequence analysis method has been carried out at Japan Atomic Energy Agency for the development of a probabilistic safety assessment method for nuclear fuel facilities. A computer tool has been developed to simulate the boiling event of reprocessed liquid waste, which is postulated to occur due to the loss of the cooling function at a fuel reprocessing plant. The thermodynamic properties of a nitric acid solution containing radioactive waste in boiling and condensing states are necessary to quantitatively assess the amount of radioactive materials transferring to the gas phase. The developed tool simulates the boiling and condensation processes of liquid waste based on ebullioscopy. A simulation study demonstrated that the behaviors of liquid waste temperature and nitric acid concentration were in good agreement with the experimental results.