It is necessary to consider the effect of photoneutrons produced by photonuclear reactions in the shielding calculation of a medical linac room with incident electron energies greater than 10 MeV. For photonuclear reaction files, the validation of photoneutron energy distributions has not been reported. We compared the evaluated data of photoneutron energy distributions in LA150 and JENDL/PD-2016.1 with the experimental data for 11 nuclides taken from the EXFOR database. For dominant shielding materials of linac, we validated the tendency of energy distributions by comparing the experimental data of neighborhood nuclides. Consequently, we found problems in the evaluations of the photoneutron energy distributions of the photonuclear reaction files.
To determine the background radiation level in an area affected by the Fukushima Daiichi nuclear power plant accident in 2011, natural terrestrial gamma rays had been measured using portable germanium detectors repeatedly from 2013 through 2019, at 370 locations within an area of 80 km radius around the Fukushima Daiichi nuclear power plant. At these locations, radioactive 238U, 232Th, and 40K concentrations in soil and air kerma rates at a height of 1 m above the ground due to terrestrial gamma rays were obtained by the method indicated in ICRU report 53. The average 238U, 232Th, and 40K concentrations were 18.8 (standard deviation, SD: 6.37), 22.7 (SD: 11.7), and 428 (SD: 163) Bq/kg, respectively, and the average air kerma rate over the area was found to be 0.0402 (SD: 0.0146)μGy/h. The obtained air kerma rates were compared with those reported in the literature. It was confirmed that the measured data positively correlated with each other with a regression coefficient close to one and agreed within a factor of two. A trend similar to that in previous findings was observed, that is, the air kerma rates at locations geologically classified as granite and rhyolite zones were statistically significantly higher than those at other locations.
Some of the Cs inside the Fukushima Daiichi Nuclear Power Station would be deposited in chemical forms such as CsI and Cs2MoO4. Since Cs compounds are generally water-soluble, it is predicted that the migration of Cs through the aqueous phase occurs in the long term. Knowledge of the solubility in water is required as basic data for such migration behavior evaluation. Therefore, this study was conducted to investigate the dissolution properties of CsI and Cs2MoO4 in water at 20℃ and 25℃. The solubilities of CsI at 25℃ calculated using thermodynamic data and the Pitzer ion interaction model were in good agreement with the literature value. It was found that the literature value of CsI at around room temperature is highly reliable. The experimental value of CsI at 20℃ obtained by the OECD test guideline 105 flask method (test guideline) was also in good agreement with the literature value. The measured solubility of Cs2MoO4 was 256.8±12.7 (g/100 g H2O) at 20℃ using the test guideline. This measured solubility of Cs2MoO4 was found to be comparable to those of other alkaline molybdates and considered to be more reliable than the literature value.
The testimony of the Fukushima daiichi nuclear accident was used to analyze the factors that led to insufficient safety measures for nuclear power plants in Japan, focusing on the relationship between people in nuclear safety and local citizens. Analysis results revealed that not only were there issues concerning people in nuclear safety themselves, but the complex interaction between them and local citizens was also an important factor. Furthermore, the fact that safety measures for nuclear power plants had improved very little until after the accident is consistent with the Drift into Failure Model. In this model, when some elements of a system are modified to respond to problems, the entire system drifts into failure (such as accidents) because of the unexpected interactions among those modified elements. Although the legislation on Periodic Safety Review (PSR) in 2003 partially improved nuclear power plant safety, it interacted with other elements and led to inadequate safety measures in Japan.