A trend analysis of human error events is important for preventing the recurrence of human error events. We propose a new method for identifying the common characteristics from results of trend analysis, such as the latent weakness of organization, and a management process for strategic error prevention. In this paper, we describe a trend analysis method for human error events that have been accumulated in the organization and the utilization of the results of trend analysis to prevent accidents proactively. Although the systematic analysis of human error events, the monitoring of their overall trend, and the utilization of the analyzed results have been examined for the plant operation, such information has never been utilized completely. Sharing information on human error events and analyzing their causes lead to the clarification of problems in the management and human factors. This new method was applied to the human error events that occurred in the Rokkasho reprocessing plant from 2010 October. Results revealed that the output of this method is effective in judging the error prevention plan and that the number of human error events is reduced to about 50% those observed in 2009 and 2010.
We made a descriptive inference about the role of the U.S. National Academies in the U.S. radioactive waste disposal projects on the basis of literature-based information and compared the U.S. National Academies with the Science Council of Japan to determine their implications on the progress of social acceptability of radioactive waste disposal projects in Japan. The descriptive inference was made as follows. We described the organizational characteristics of the U.S. National Academies and the U.S. federal governments related to the projects. We outlined the related bills and demonstrated chronologically the activities related to the projects by the U.S. National Academies and the U.S. Government. As a consequence, we identified some specific roles that the U.S. National Academies played in the U.S. radioactive waste disposal projects. The U.S. National Academies have acted not only as a scientific and engineering adviser for the governments but also as an anchor for some political decision making or judicial actions. Furthermore, we analyzed the credibility of the Science Council of Japan and the U.S. National Academies from the viewpoint that a reliable third party must exhibit fairness, expertise and continuity. From the results of the comparison, it was found that the Science Council of Japan has the possibility to become a reliable third party that can help the radioactive waste disposal projects in Japan.
A prediction method for water temperature in a spent fuel pit of a PWR has been developed to calculate the increase in water temperature during the shutdown of cooling systems. In this study, the prediction method was extended to calculate the water level in a spent fuel pit during loss of all AC powers, and predicted results were compared with data of spent fuel pools in the Fukushima Daiichi Nuclear Power Station. The calculations gave reasonable results, but overestimated the decreasing rate of the water level and water temperature. This result indicated that decay heat was overestimated and evaporation heat transfer from the water surface was underestimated. Results of calculations with 80% decay heat and 155% (No. 4 pool) or 230% (No. 2 pool) evaporation heat flux were in good agreement with data. The data-fitted evaporation heat fluxes agreed rather well with the evaporation heat transfer correlation proposed by Fujii et al.
In this paper, we present the three-dimensional finite element seismic response analysis of the full-scale boiling water reactor BWR5 at the Kashiwazaki-Kariwa Nuclear Power Plant subjected to the Niigata-ken Chuetsu-Oki (NCO) earthquake that occurred on 16th July 2007. During the earthquake, the automatic shutdown of the reactors was performed successfully. Although the monitored seismic acceleration significantly exceeded the design level, it was found through in-depth investigation that there was no significant damage of the reactor cores or other important systems, structures and components (SSCs). In the seismic design commonly used in Japan, a lumped mass model is employed to evaluate the seismic response of SSCs. Although the lumped mass model has worked well so far for a seismic proof design, more precise methods should be developed to understand response behaviors visually. In the present study, we propose the three-dimensional finite element seismic response analysis of the full-scale and precise BWR model in order to directly visualize the dynamic behaviors of this model. Through the comparison of the analysis results, we discuss the characteristics of both models. The stress values were also found to be generally under the design value.
Clearance levels for uranium isotopes have been recently authorized in Japan. The measurement of those elements can be disregarded when the nominal of the element (D/C), expressed as (D/C)*, is less than 10−3, where D is the specific radioactivity concentration of nuclides, C is the clearance level of nuclides, and (D/C)* is defined as (D/C) divided by the highest value of (D/C)'s in the element constitutions of uranium waste. In this study, the concentration of nuclides in reprocessed uranium was evaluated using ORIGEN2 burnup analyses and the most appropriate decontamination factors for determining the (D/C)* values and their influence on clearance application in the uranium fuel fabrication plant. It was concluded that nuclides other than five isotopes, 232U, 234U, 235U, 236U, and 238U, can be disregarded with regards to clearance application in the uranium fabrication plant, regardless of operation conditions, whether the fuel is fabricated by receiving reprocessed uranium or not.
Leachates from cementitious grouting materials used for reducing water inflow are hyperalkaline and chemically reactive with the engineered barriers and host rock for geological disposal of high-level radioactive waste. Evaluation methods for long-term alteration of the fractured rock have been developed since the extent of chemical modification may influence the transport and retardation properties of radionuclides in the far field. The present study shows the current status of the development of the methodology (i.e., procedure, models, and simulation codes) for evaluating the effects of cementitious grouting materials on groundwater and rock.