Current status and issues for clearance, 5; Concept of restricted use of contaminated rubbles in the Fukushima Daiichi NPS

Shimada, Taro; Miwa, Kazuji; Takeda, Seiji

Nihon Genshiryoku Gakkai-Shi ATOMO, 61(7), p.531 - 534, 2019/07

Rubbles less than 5 Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. However, there is no precedent for establishing the reference values such as dose and/or concentration for reuse or recycling under the existing exposure situation. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. In addition, based on the concept, we calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.

Disposal and recycling; Safer disposal and reassuring recycling

Nishihara, Kenji

ImPACT Fujita Puroguramu Kokai Seika Hokokukai "Kaku Henkan Niyoru Koreberu Hoshasei Haikibutsu No Ohaba Na Teigen, Shigenka" Seika Hokokusho, Shiryoshu, p.28 - 31, 2019/03

In this project, long-lived fission products (LLFP) contained in conventional high-level radioactive wastes are separated and their life is reduced, and elements that can be used as resources are separated. By shortening the life of LLFP, it has been shown that it may be possible to dispose in intermediate depth of several tens of meters, meeting safety requirements, instead of geological disposal. In addition, for reassuring recycling of usable elements, possible exposure pathways were evaluated to estimate the safe concentration level of radioactivity.

Dose estimation in recycling of decontamination soil resulting from the Fukushima NPS accident for road embankments

Takai, Shizuka; Sawaguchi, Takuma; Takeda, Seiji

Health Physics, 115(4), p.439 - 447, 2018/10

https://doi.org/10.1097/HP.0000000000000904

After the Fukushima Nuclear Power Station accident, large quantities of radiocesium-contaminated soil generated from decontamination activities have been stored in the Fukushima Prefecture. To reduce the disposal volume, the Ministry of the Environment of Japan has presented a policy to recycle low-radioactive decontamination soil limited to civil engineering structures. However, there has been no practical instance or safety assessment of decontamination soil recycling. In this study, the way of ensuring the safety for decontamination soil recycling for road embankments was discussed. First, based on Japanese construction standards, additional doses to workers and the public in construction and service scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials, where all additional doses meet the radiation criterion of 1 mSv y, was derived to be 6,000 Bq kg. To confine additional doses to the public in a service scenario below 0.01 mSv y, soil slope protection of 40 cm or more was needed. Finally, additional doses in a disaster scenario were confirmed to be below 1 mSv y.

Estimation of doses from radioactively contaminated disaster wastes reused for pavements

Sawaguchi, Takuma; Takeda, Seiji; Kimura, Hideo; Tanaka, Tadao

Hoken Butsuri, 50(1), p.36 - 49, 2015/03

It is desirable that the disaster wastes contaminated by radioactive cesium after the severe accident at the Fukushima Nuclear Plant are reused as much as possible in order to minimize the quantity to be disposed of. Ministry of the Environment showed the policy that the wastes containing cesium of higher concentration than the clearance level (100 Bq/kg) were reusable as materials of construction such as subbase course materials of pavements under controlled condition with measures to lower exposure doses. In this study, in order to provide technical information for making a guideline on the use of contaminated concrete materials recycled from disaster wastes as pavement, doses for workers and the public were estimated, and the reusable concentration of radioactive cesium in the wastes was evaluated. It was shown that the external exposure of the public (children) residing near the completed pavement gave the minimum radiocesium concentration in order to comply with the dose criteria. The recycled concrete materials whose average concentration of cesium lower than 2,700 Bq/kg can be used as the subbase course materials of pavements.

Environment purification technology using ionizing radiation

Kojima, Takuji

Hoshasen, 29(2), p.77 - 85, 2003/04

http://ci.nii.ac.jp/naid/10011475414

The radiation technologies for environment conservation are useful for purification of pollutants contained in flue gas or wastewater at very low concentration which is difficult to perform by conventional methods: removal using fine filter or charcoals and decomposition using catalysis at high temperature, etc. This paper reviews some examples of radiation application to removal of SO and NO from coal-combustion flue gases, decomposition of dioxin in gas emitted through the incinerator, decomposition of gaseous toxic volatile organic compounds in off gas, reuse of agricultural wastes.

Derivation of clearance levels for solid materials in Japan

Sakai, Akihiro; Okoshi, Minoru

Radiation Risk Assessment Workshop Proceedings, p.175 - 186, 2003/00

To establish the clearance levels, the Nuclear Safety Commission (NSC) has been discussing the clearance levels since May 1997. The NSC derived the unconditional clearance levels for the solid materials, namely concrete and metal, arising from the operation and dismantling of nuclear reactors and post irradiation examination (PIE) facilities. Two destinations of the cleared materials, namely disposal and recycle/reuse, were considered. Deterministic calculation models were established to assess individual doses resulting from 73 exposure pathways, and realistic parameter values were selected considering the Japanese natural and social conditions. The clearance levels for 21 radionuclides of nuclear reactors and for 49 of PIE facilities were derived as radioactivity concentration equivalent to the individual doses of 10 Sv/y. Most of calculated clearance levels were nearly the same as those shown in IAEA-TECDOC-855. Some, however, were different. It is considered that the major reasons depend on differences of fixed scenarios and of selected values of parameters.

Study on measurement of spatial dose rates from simulated products made from recycled metal below clearance levels arising from dismantling of nuclear facilities (Contract research)

Okamoto, Akiko; Kitami, Yasuo*; Ando, Yoshiaki*; Nakamura, Hisashi; Saito, Kimiaki; Nakashima, Mikio

JAERI-Tech 2002-051, 40 Pages, 2002/06

JAERI-Tech-2002-051.pdf:3.63MB

In order to contribute to safety assessment of recycling products made from dismantling metal wastes, metal ingots containing Co were produced and spatial dose rates from the ingots were evaluated by gamma-ray measurement and calculation. Stripping operations were made using detector response functions calculated by Monte Carlo program to derive spatial dose rates from measured gamma-ray spectra. In the computer simulation, Monte Carlo and point kernel calculation codes were used. Agreement between measured and calculated values was satisfactory in spite of an extremely low concentration of Co in the ingots and a complicated geometric condition between detector and samples.

Derivation methods for clearance levels and safety assessments for very low-level radioactive waste disposal

Okoshi, Minoru

KURRI-KR-56, p.39 - 57, 2001/03

no abstracts in English

Study on reducing the generation of general waste

Aoki, Isao; ; Haga, Tetsuya; ; Sudo, Katsuo; Tsunashima, Yasumichi;

JNC TN8420 2000-005, 42 Pages, 2000/04

JNC-TN8420-2000-005.pdf:2.09MB

On August 1999, the Director of Tokai Work proposed an activity regarding recycling and reuse of general waste generated from Tokai Works. The activity was initiated by the Waste Management and Fuel Cycle Research Center, and is now being in progress through out the Tokai Works. In the course of this activity, Plutonium Fuel Center had settled the Working Group and the issues related to the waste reduction have been examined. This report collects the problems that became obvious through the survey of existing segregation method, treatment process, and the amount of the waste generation, and accounts for the concrete methodology for the recycling and reuse of general waste. In order to reduce waste, it is necessary to aware of the facing issues and adopt the countermeasures proposed in this report whenever possible. The activity will then leads us to reduce waste generation, which in turn will enable us to make 100 % waste recycling possible.

Deterministic approach towards establishing of clearance levels in Japan

Okoshi, Minoru; Sakai, Akihiro; Yoshimori, Michiro; Yamamoto, Hideaki; Takahashi, Tomoyuki; Kimura, Hideo

Proc. of 7th Int. Conf. on Radioactive Waste Management and Environmental Remediation (ICEM'99)(CD-ROM), 8 Pages, 1999/09

no abstracts in English