No abstract

Japan's nuclear disaster prevention system entered review regarding the 2011 Fukushima Daiichi Nuclear Power Plant accident and the Nuclear Emergency Response Guideline was revised in 2015. One important task for enhancing the nuclear disaster prevention system is to improve residential evacuations. Evacuating residents during nuclear disasters has unique problems, such as radiation contamination by substances released into the atmosphere, in addition to the problems of natural disasters, such as transportation disruptions. The Nuclear Emergency Response Guideline released by the Nuclear Regulatory implemented for evacuees in case of nuclear disaster (Evacuation Exit Inspection: EEI)." The EEI was proposed after the reports point out the problems faced by local governments concerning evacuations. This report explains the criteria used to implement protections during nuclear facility emergencies and the content of the EEI. It also describes the Aomori Prefecture

To obtain a better understanding of recent tritium concentration and its seasonal cycle in Japan, monthly precipitation samples were collected in Hokkaido, Gifu and Okinawa prefectures from June 2014 to December 2017. The arithmetic mean ( ± standard deviation) of tritium concentrations in precipitation samples from Hokkaido, Gifu and Okinawa were estimated to be 0.62 ± 0.27 Bq L−1, 0.32 ± 0.12 Bq L−1 and 0.13 ± 0.05 Bq L−1, respectively. These results indicate that the concentrations increase with latitude. In addition, the highest and the lowest concentrations appeared in spring and summer, respectively. To clarify the origins and sources of these cycles, further analyses of chemical compositions of precipitation and meteorological conditions are needed.

Soil samples from the surface to a 5 cm depth were collected at a residential house in Koriyama City, Fukushima Prefecture using a scraper plate every three months from March 2014 to September 2014 to evaluate the vertical distribution profiles and inventories of 134Cs and 137Cs in soil. The vertical distribution profiles of radiocesium (134Cs and 137Cs) in soil showed that greater than 86% of the total radiocesium was absorbed in the upper 2 cm 3 years after the accident. Radiocesium in the surface layer seems to move to the lower layer over time. The migration of radiocesium in surface layer might be influenced by the ground surface runoff by rainfall. Radiocesium inventories in June increased significantly over the short period between March and June. In contrast, the radiocesium inventories in September did not increase significantly compared to the values in June. Radiocesium resuspension and deposition caused by decontamination work and meteorological events might be one possible reason for the increased radiocesium inventories observed in June.

The absorbed dose rate in air was measured at the National Institute for Fusion Science (NIFS) site before the deuterium plasma experiment in the Large Helical Device (LHD). A pocket survey meter was used for the measurement of 1 cm dose equivalent rates in units of µSv h −1 and these results were converted to absorbed dose rates in air (units: nGy h −1 ) using a conversion factor. The arithmetic mean of the absorbed dose rates in air based on 257 measurement points at NIFS site was 45 nGy h −1 . The result of this study suggests that the building material and/or paving stone enhance the dose rates in air at the NIFS site. The Large Helical Device (LHD), which was constructed in 1998 at the National Institute for Fusion Science (NIFS) [1], is one of the largest heliotron-type plasma experiment device with superconducting coils. A new project-The deuterium plasma experiment (DD experiment) to obtain higher performance plasma-is scheduled to begin in 2017 and last for nine years. In the DD experiments, tritium and neutron are generated as a result of a nuclear fusion reaction in the deuterium plasma.where, D is deuterium, T is tritium, p is photon, 3 He is helium-3, and n is neutron. The maximum annual amount of tritium production is estimated to be approximately 37 GBq in the first 6 years, and 55.5 GBq in the remaining 3 years. More than 95% of the produced tritium is planned to be removed using a tritium recovery system [2,3]. The DD experiments on the LHD will be conducted in consideration of the DD neutron yield [4,5]. To evaluate the experiment's impact on the environment precisely, it is important to understand the background radiation levels in the environment surrounding the NIFS site. We have monitored about tritium concentration in the natural water collected at Toki, Tajimi, and Mizunami cities since 1982 before the construction of the NIFS facilities. We have also monitored tritium concentration in tap water at the Institute of Plasma Physics, Nagoya University, located approximately 30 km southwest of the NIFS site. Part of the data on natural water has already been reported [6]. In addition, recent tritium concentrations in air and plant samples have been reported [7,8]. However, there are no detailed reports