The purpose of this study is to clarify whether reports of nuclear accidents, particularly the damage done by the 2007 Niigata-ken Chuetsu-Oki earthquake to the Kashiwazaki-Kariwa nuclear power plant in Niigata, Japan, tend to be exaggerated by national media. News related to the Kashiwazaki incident was compared with that for nine other high-profile accidents in Japan, including the 1999 JCO critical accident and the 2005 JR-West Fukuchiyama Line derailment. Articles were extracted from four national newspapers in Japan, focusing on the 30 issues immediately following each accident. The numbers of articles and top stories related to the relevant accidents appearing on the front pages of the newspapers were counted. Based on these numbers, the Kashiwazaki incident was reported at a level similar to the JCO accident and Fukuchiyama line derailment in some newspapers, although these two accidents were more serious than the Kashiwazaki incident. This suggests that at least some newspapers in Japan sensationalized reports of the Kashiwazaki incident.
Since quality control issues for vitrified waste are defined mainly with the focus on the transport and interim storage of the waste rather than the long-term safety of geological disposal, they do not cover inventories of long-lived nuclides that are of most interest in the safety assessment of geological disposal. Therefore, we suggest a flow chart for the assessment of inventories of long-lived nuclides in the vitrified waste focusing on the measured values. This includes an indirect assessment with indicative nuclides that have been already measured in the returned vitrified wastes from abroad. In order to apply this flow chart for commercial operation, its applicability should be examined for cases with a variation in burn-up history and with an uncertainty associated with carry-over fraction at reprocessing. We started an R & D program to examine the applicability as well as to improve the reliability of the nuclide generation/decay code and the nuclear data library using liquid waste from spent fuel with a clear irradiation history. To solve the issue of quality control for vitrified waste, a comprehensive study is needed in aspects not only of geological disposal field but also of operation of a nuclear power plant, reprocessing of spent fuel and vitrification of liquid waste. This study is a pioneering study conducted to integrate them.
Soil-to-plant transfer factor (TF) is one of the important parameters in radiation dose assessment models for the environmental transfer of radionuclides. Since TFs are affected by several factors, including radionuclides, plant species and soil properties, development of a method for estimation of TF using some soil and plant properties would be useful. In this study, we took a statistical approach to estimating the TF of stable strontium (TFSr) from selected soil properties and element concentrations in plants, which was used as an analogue of 90Sr. We collected the plant and soil samples used for the study from 142 agricultural fields throughout Japan. We applied a multiple linear regression analysis in order to get an empirical equation to estimate TFSr. TFSr could be estimated from the Sr concentration in soil (CSrsoil) and Ca concentration in crop (CCacrop) using the following equation: log TFSr=−0.88·log CSrsoil+0.93·log CCacrop −2.53. Then, we replaced our data with Ca concentrations in crops from a food composition database compiled by the Japanese government. Finally, we predicted TFSr using Sr concentration in soil from our data and Ca concentration in crops from the database of food composition.
The confidentiality system concerning the physical protection of nuclear materials and nuclear facilities was enacted by revision of the Nuclear Reactor Regulation Law in 2005. We made a comparative analysis with the information security in governmental agencies or financial sectors, in order to consider the way the sensitive information management concerning the physical protection of nuclear materials and nuclear facilities should be. The considerations in this paper are as follows. (1) In order to secure a suitable level of security, close cooperation should be achieved among related governmental agencies. (2) A cycle that continuously evaluates whether suitable management is performed should be established. (3) Excessive secretiveness should be eliminated. (4) An information-sharing system among the related persons beyond the frame of governmental agencies and electricity companies should be established. (5) Improvement in the social acceptability of the sensitive information management is important. (6) Although it is important to perform evaluation by the consideration of suitable balance with information disclosure, it is also important that it is positively shown to society.
Fission product (FP) aerosol trapping along the leakage paths of degraded containment penetrations during a severe accident was investigated. Prior to this aerosol trapping test, several actual electrical penetration assemblies (EPAs) and hatch flange gaskets were degraded under prototypical severe accident conditions in a reactor containment. Then, the aerosol trapping test at the leakage path was conducted. Cesium iodide (CsI) was used as a FP aerosol in the test. The aerosol trapping effect along the leakage paths was expressed as a decontamination factor (DF) and the average values were about 740 for the low-voltage module and about 14 for the flange gaskets. The overall DF value of a typical BWR was estimated at about 450, using the average DF value and a number of containment penetrations of each type. These results were reflected in the severe accident analysis by the MELCOR code. The total amount of FP leaked from containment was reduced to around 50 to 70% compared with that determined by the original MELCOR analysis 1 day after a typical BWR severe accident.