Confirmation of the sustainability of decontamination effects in public facilities and prediction of future air dose rates

Kusakabe, Kazuaki*; Watanabe, Masanori; Nishiuchi, Masashi*; Yamasaki, Takuhei*; Inoue, Hiromi*

Kankyo Hoshano Josen Gakkai-Shi, 11(1), p.15 - 23, 2023/03

The spread of radioactive materials caused by the Fukushima Daiichi Nuclear Power Plant accident that occurred in March 2011 contaminated a wide area that includes Fukushima Prefecture. Although air dose rates in Fukushima Prefecture have been steadily decreasing because of decontamination and the physical decay of radioactive materials, it is important to confirm the sustainability of decontamination effects in living areas and to predict future trends in air dose rates to reassure residents who are concerned regarding radiation exposure. This report aims to confirm the sustainability of the decontamination effects in public facilities after decontamination on a continuous and detailed basis, and to verify whether the future transition in air dose rates can be predicted using existing model. The air dose rates in public facilities after decontamination were measured via fixed-point and walking surveys, and the changes in air dose rates were clarified quantitatively for each facility. The measured values were compared with values obtained using existing model, and prediction accuracy was considered. The results showed that there was no evident recontamination after decontamination at any of the surveyed facilities, indicating that the decontamination effects were sustained. It was also confirmed that future trends in air dose rates at the facilities after decontamination could be accurately predicted by existing model. Key words: air dose rate, decontamination, future prediction, public facilities.

Survey results for the transition of the air dose rate after the Cabinet Office decontamination model demonstration project; 1st-11th survey results summary (Contract research)

Kawase, Keiichi; Kitano, Mitsuaki; Watanabe, Masanori; Yoshimura, Shuichi; Kikuchi, Shiro; Nishino, Katsumi*

JAEA-Review 2017-006, 173 Pages, 2017/03

JAEA-Review-2017-006.pdf:35.6MB
JAEA-Review-2017-006-appendix(CD-ROM).zip:0.52MB

Survey of a transition of the air and surface dose rate was conducted for the area where the Cabinet Office decontamination model demonstration project was implemented. The area includes 15 districts in 9 municipalities identified by the Ministry of the Environment. We investigated 11 times from October, 2012 to October, 2015. Measurement of the air dose rate in this study was carried out in two methods using the fixed-point measurement and gamma plotter H using a NaI scintillation survey meter etc. As fixed-point measurement, set measurement point in the first survey for (fixed point), it was subjected to measurement of the surface dose rate to continue (1cm height) and space dose rate (1m height). In addition surface specific dose rate distribution measurement using a gamma plotter H (5cm and 1m height) was also performed together. As a result of the fixed-point measurement and gamma plotter H surface measurements, space dose rate from the first survey to the 11th survey shows the downward trend. We consider that there is no movement of radioactive pollutants from outside decontamination model project area into decontamination model project area.

Report for "FY 2012 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant Accident" (Contract research)

Watanabe, Masahisa; Umemiya, Noriko; Tagawa, Akihiro; Kawase, Keiichi; Noguchi, Shinichi; Sakazume, Yoshinori; Watanabe, Masanori; Tokizawa, Takayuki

JAEA-Review 2013-052, 232 Pages, 2014/03

JAEA-Review-2013-052.pdf:26.42MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2012 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 15 candidates. JAEA was commissioned by the Ministry of the Environment, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out technical advice of demonstration test and evaluation of 15 technologies (e.g., decontamination technology of Burned ash washing and Pond Dredging) to perform decontamination of the environment.

Conceptual design of irradiation experimental device for 12 inch NTD-Si ingot in JRR-4 (Contract research)

Yagi, Masahiro; Watanabe, Masanori; Oyama, Koji; Komeda, Masao; Yamamoto, Kazuyoshi; Kashima, Yoichi

JAEA-Technology 2008-015, 91 Pages, 2008/03

JAEA-Technology-2008-015.pdf:22.92MB

The irradiation experimental device is designed by surveying analytically an irradiation condition to improve the neutron flux distribution of the radial direction on NTD-Si by using neutron transportation calculation Monte Carlo calculation code MCNP5 in order to develop neutron irradiation technology for the large-diameter silicon to 12 inches diameter at the maximum and an irradiation experiment will be performed in JRR-4. Thus the validity of the design technique of the irradiation device will be confirmed by this experiment. The irradiation experimental device is installed in the side of the core tank outer wall. A 12 inches silicon ingot of 60cm in height is irradiated in a reflector cover which surrounds the silicon ingot for increasing the flux. The silicon ingot is rotated during irradiation in order to require the condition of uniformly distributed thermal neutron flux over whole circumferences. A uniform irradiation condition was achieved by the pass-through core method, in which silicon ingot moved up and down with rotating. The condition was satisfied when silicon was covered with the thermal neutron filter, which is made from aluminum alloy of thickness of 2mm with natural boron element ratio of 1.5%, and was moved in the range from -42mm to 22mm for the center of the reactor core. The deviation of the Si-30 neutron absorption reaction rate was range from -3.2% to +5.3% in the intermediate volume of 40cm height and the neutron absorption reaction ratio of the circumference to the center was within 1.09 in the volume.

Conceptual design about the 12-inch NTD-Si irradiation experimental device, 1; Study of uniform irradiation condition in NTD-Si ingot with large-diameter by nuclear analyses

Yagi, Masahiro; Kashima, Yoichi; Watanabe, Masanori; Yamamoto, Kazuyoshi

no journal, , 

The irradiation experimental device is designed by surveying analytically an irradiation condition to improve the neutron flux distribution of the diameter direction on NTD-Si by using Monte Carlo calculation code MCNP5 in order to develop neutron irradiation technology for the large-diameter silicon to 12 inches diameter at the maximum. Some irradiation experiment will be performed to confirm validity of the design technique in JRR-4 by using the experimental device for the 12 inches NTD-Si ingot. The experimental device is installed in the No.1 reactor pool side of the core tank outer wall. The 12 inches silicon of 60 cm in height is irradiated in a reflector cover which surrounds the silicon for increasing the flux. The silicon also is irradiated with rotating in order to require the condition of uniformly distributed thermal neutron flux over whole circumferences. A uniform irradiation condition was achieved by the pass-through core method with adding the thermal neutron filter which covers the silicon surface and is able to move up and down with rotating. The condition was satisfied when silicon was covered with the thermal neutron filter, which is made from aluminum alloy of 2 mm thickness with natural boron element ratio of 1.5%, and was run in the range from -42 mm to 22 mm for the center of the reactor core. The deviation of the Si-30 neutron absorption reaction rate was range from -3.22% to +5.27% in the intermediate volume of 40 cm height and the neutron absorption reaction ratio of the circumference to the center was within 1.09 in the volume.

Design of an uniform-irradiation test facility for large-diameter silicon

Yamamoto, Kazuyoshi; Komeda, Masao; Yagi, Masahiro; Watanabe, Masanori; Sagawa, Hisashi

no journal, , 

no abstracts in English

Result of demonstration tests on decontamination technology, 10; The Knowledge from the demonstration of the process of insolubilization and solidification of incineration ash from demonstration tests results

Sakazume, Yoshinori; Tokizawa, Takayuki; Noguchi, Shinichi; Kawase, Keiichi; Motohashi, Jun; Watanabe, Masanori

no journal, , 

no abstracts in English

Estimation of dose reduction factor before and after decontamination

Ishizaki, Azusa; Mori, Airi; Kawase, Keiichi; Kato, Mitsugu; Watanabe, Masanori; Aoki, Isao; Munakata, Masahiro

no journal, ,