Soil dust and bioaerosols as potential sources for resuspended Cs occurring near the Fukushima Dai-ichi Nuclear Power Plant

Ota, Masakazu; Takahara, Shogo; Yoshimura, Kazuya; Nagakubo, Azusa; Hirouchi, Jun; Hayashi, Naho; Abe, Tomohisa; Funaki, Hironori; Nagai, Haruyasu

Journal of Environmental Radioactivity, 264, p.107198_1 - 107198_15, 2023/08

https://doi.org/10.1016/j.jenvrad.2023.107198

One of the current major radiation exposure pathways from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident-fallout is inhalation of the re-suspended Cs occurring in air. While wind-induced soil particle resuspension has been recognized as a primary mechanism of Cs resuspension, studies following the FDNPP accident suggested that fungal spores can be a significant source of the atmospheric Cs particularly in the rural areas such as difficult-to-return zone (DRZ). To elucidate the relative importance of the two resuspension phenomena, we propose a model simulating resuspension of Cs as soil particles and fungal spores, and applied it to DRZ. Our model's calculation showed that soil particle resuspension was responsible for the surface-air Cs observed during winter-spring, but could not account for the higher Cs concentrations observed in summer-autumn. The higher concentrations in the summer-autumn were in general reproduced by implementing fungal spore Cs emission, that replenished low soil particle Cs resuspension in that period. According to our model's concept, Cs accumulation in fungal spores and high spore emission rate characterized by the rural environment were likely responsible for the abundance of spore Cs in the air. It was inferred that the influence of the fungal spores on the atmospheric Cs would last longer since un-decontaminated forests still exist in DRZ.

Establishing an evaluation method for the aging phenomenon by physical force in fuel debris

Suzuki, Seiya; Arai, Yoichi; Okamura, Nobuo; Watanabe, Masayuki

Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07

https://doi.org/10.1080/00223131.2022.2159559

The fuel debris, consisting of nuclear fuel materials and reactor structural materials, generated in the accident of Fukushima Daiichi Nuclear Power Plant can become deteriorated like rocks under the changes of environmental temperature. Although the fuel debris have been cooled by water for 10 years, they are affected by seasonal and/or day-and-night temperature changes. Therefore, in evaluating the aging behavior of the fuel debris, it is essential to consider the changes in environmental temperature. Assuming that the fuel debris are deteriorated, radioactive substances that have recently undergone micronization could be eluted into the cooling water, and such condition may affect defueling methods. We focused on the effect of repeated changes in environmental temperature on the occurrence of cracks, and an accelerated test using simulated fuel debris was carried out. The length of the crack increases with increasing number of heat cycle; therefore, the fuel debris become brittle by stress caused by thermal expansion and contraction. In conclusion, it was confirmed that the mechanical deterioration of the fuel debris is similar to that of rocks or minerals, and it became possible to predict changes in the length of the crack in the simulated fuel debris and environmental model.

Applicability of differential die-away self-interrogation technique for quantification of spontaneous fission nuclides for fuel debris at Fukushima Daiichi Nuclear Power Plants

Nagatani, Taketeru; Sagara, Hiroshi*; Kosuge, Yoshihiro*; Nomi, Takayoshi; Okumura, Keisuke

Journal of Nuclear Science and Technology, 60(4), p.460 - 472, 2023/04

https://doi.org/10.1080/00223131.2022.2114958

Mental health measures for the staff of nuclear research and development institution mobilized in dealing with residents during the nuclear disaster caused by the Great East Japan Earthquake

Tomotsune, Yusuke; Yajima, Mayumi; Okuno, Hiroshi; Yamamoto, Kazuya

Rodo Anzen Eisei Kenkyu, 16(1), p.29 - 43, 2023/02

https://doi.org/10.2486/josh.JOSH-2021-0017-JI

During the first year of the accident at the Fukushima Daiichi Nuclear Power Station caused by the Great East Japan Earthquake in March 2011, a total of about 45,000 employees of Japan Atomic Energy Agency (JAEA) left their original workplaces to engage in telephone counseling, assistance of temporary return, and environmental monitoring. In particular, the staff who worked on the telephone counseling service, which directly contacted the residents, suffered from the stress associated with emotional labor. Systematic mental health care to the staff who engaged in these tasks was provided them in the Nuclear Fuel Cycle Engineering Laboratories of the JAEA. This paper considers this activity as a concrete example of "support for supporters" and discusses the mental health of the staff who provide support to the residents in a nuclear disaster.

Reactivity estimation based on the linear equation of characteristic time profile of power in subcritical quasi-steady state

Yamane, Yuichi

Journal of Nuclear Science and Technology, 59(11), p.1331 - 1344, 2022/11

https://doi.org/10.1080/00223131.2022.2053221

The reactivity was estimated from a time profile of neutron count rate or a simulated data in a quasi-steady state after sudden change of reactivity or external neutron source strength. The estimation was based on the equation of power in subcritical quasi-steady state. The purpose of the study is to develop the method of timely reactivity estimation from complicated time profile of neutron count rate. The developed method was applied to the data simulating neutron count rate created by using one-point kinetics code, AGNES, and Poisson-distributed random noise and to the transient subcritical experiment data measured by using TRACY. The result shows that the difference of the estimated and reference value was within about 5% or less for ( -1) for simulated data and within about 7% or less for -1.4 and -3.1 for the experimental data. It was also shown that the possibility of the reactivity estimation several ten seconds after the status change.

Validation of a model for estimating individual external dose based on ambient dose equivalent and life patterns

Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Sato, Tetsuro*

Journal of Radiation Protection and Research, 47(2), p.77 - 85, 2022/06

https://doi.org/10.14407/jrpr.2021.00290

After the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, a model was developed to estimate the external exposure doses for residents who were expected to return to their homes after evacuation orders were lifted. However, the model's accuracy and uncertainties in parameters used to estimate external doses have not been evaluated. This study validates the model's accuracy by comparing the estimated effective doses with the measured personal dose equivalents. The personal dose equivalents and life pattern data were collected for 36 adult participants who lived or worked near the FDNPS in 2019. The estimated effective doses correlated significantly with the personal dose equivalents, demonstrating the model's applicability for effective dose estimation. However, the lower value of the effective dose relative to personal dose equivalent indoors could be because the conversion factor from ambient dose equivalent to effective dose did not reflect the actual environment.

Result of measurement of the ambient dose equivalent rates by car-borne surveys using KURAMA-II from 2012 until 2019

Ando, Masaki; Saito, Kimiaki

JAEA-Technology 2021-032, 66 Pages, 2022/03

JAEA-Technology-2021-032.pdf:3.84MB

Since the occurrence of the accident at the TEPCO Fukushima Daiichi Nuclear Power Station, the Japan Atomic Energy Agency (JAEA) has been conducting a series of car-borne survey over a wide area in the eastern part of Japan using the monitoring system KURAMAII. In this report, outline of the car-borne surveys are summarized and the following characteristics of the temporal changes in each prefecture and region were investigated using the measured data obtained from 2012 to 2019; 1) Average and maximum values for each prefecture for the six years from 2014 to 2019, 2) Average values for each prefecture from 2012 to 2019, 3) Average values for each evacuation order area category, regional category, and northern Soso-area municipality in Fukushima Prefecture from 2012 to 2019, and 4) Average and maximum values for each municipality in each prefecture for four times (at almost two-year intervals) of the measurement results from 2012 to 2018.

Comparison of dose rates from four surveys around the Fukushima Daiichi Nuclear Power Plant for location factor evaluation

Sanada, Yukihisa; Ishida, Mutsushi*; Yoshimura, Kazuya; Mikami, Satoshi

Journal of Radiation Protection and Research, 46(4), p.184 - 193, 2021/12

https://doi.org/10.14407/jrpr.2021.00171

no abstracts in English

Preparation of carbonate slurry simulating chemical composition of slurry in overflowed high integrity container and evaluation of its characteristics

Horita, Takuma; Yamagishi, Isao; Nagaishi, Ryuji; Kashiwaya, Ryunosuke*

JAEA-Technology 2021-012, 34 Pages, 2021/07

JAEA-Technology-2021-012.pdf:2.1MB
JAEA-Technology-2021-012(errata).pdf:0.18MB

Waste mainly consisting of carbonate precipitates (carbonate slurry) from the Advanced Liquid Processing System (ALPS) and the improved ALPS at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Holdings, Inc. have been storing in the High Integrity Container (HIC). The supernatant solution of carbonate slurry contained in some of HICs were overflowed in April of 2015. The all of level of liquid in the HICs were investigated; however, almost of the HICs were under the level of overflow. The mechanism of overflow suggested to be depending on the difference of the properties of the carbonate slurry such as the retention/release characteristics of the bubbles. Therefore, in order to clarify the mechanism of leakage, the repeatability experiment was carried out by using simulated carbonate slurry. The simulated carbonate slurry was perpetrated by using the same cross-flow filter system of the actual ALPS. Moreover, the preparative conditions for the simulated carbonate slurry were the same as Mg/Ca concentration ratio in inlet water of the ALPS (raw water) and the ALPS operating conditions. The chemical characteristics of simulated carbonate slurries were revealed by ICP-AES, pH meter, etc. The density of the settled slurry layer tended to increase depending on the calcium concentration in the raw water. The bubble injection test was conducted in order to investigate the bubble retention/release behavior in the simulated carbonate slurry layer. The simulated carbonate slurry with high settling density, which was generated by high calcium concentration solution was revealed to retain the injected bubbles. Since the ratio of concentration calcium and magnesium during the carbonate slurry generation is assumed to affect the retention of bubbles in the slurry layer, the information on the composition of raw water is one of important factor for overflow of HICs.

Microparticles with diverse sizes and morphologies from mechanical and laser cutting of fuel debris simulants and geopolymer as a covering material

Zhou, Q.*; Saito, Takumi*; Suzuki, Seiya; Yano, Kimihiko; Suzuki, Shunichi*

Journal of Nuclear Science and Technology, 58(4), p.461 - 472, 2021/04

https://doi.org/10.1080/00223131.2020.1869623