Liquid decontamination using acidic electrolyzed water for various uranium-contaminated steel surfaces in dismantled centrifuge

Sakasegawa, Hideo; Nomura, Mitsuo; Sawayama, Kengo; Nakayama, Takuya; Yaita, Yumi*; Yonekawa, Hitoshi*; Kobayashi, Noboru*; Arima, Tatsumi*; Hiyama, Toshiaki*; Murata, Eiichi*

Progress in Nuclear Energy, 153, p.104396_1 - 104396_9, 2022/11

https://doi.org/10.1016/j.pnucene.2022.104396

When dismantling centrifuges in uranium-enrichment facilities, decontamination techniques must be developed to remove uranium-contaminated surfaces of dismantled parts selectively. Dismantled uranium-contaminated parts can be disposed of as nonradioactive wastes or recycled after decontamination appropriate for clearance. previously, we developed a liquid decontamination technique using acidic electrolyzed water to remove uranium-contaminated surfaces. However, further developments are still needed for its actual application. Dismantled parts have various uranium-contaminated surface features due to varied operational conditions, inhomogeneous decontamination using iodine heptafluoride gas, and changes in long-term storage conditions after dismantling. Here, we performed liquid decontamination on specimens with varying uranium-contaminated surfaces cut from a centrifuge made of low-carbon steel. From the results, the liquid decontamination can effectively remove the uranium-contaminated surfaces, and radioactive concentrations fell below the target value within twenty minutes. Although the required time should also depend on dismantled parts' sizes and shapes in their actual application, we demonstrated that it could be an effective decontamination technique for uranium-contaminated steels of dismantled centrifuges.

Current status of JAEA Ningyo-toge Decommissioning Project

Yagi, Naoto; Mita, Yutaka; Kanda, Nobuhiro

Dekomisshoningu Giho, (61), p.2 - 11, 2020/03

http://www.randec.or.jp/publish/documents/gihou/Decommissioning%20gihou_61.pdf

Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency has been conducting research and development on uranium exploration, uranium mining, uranium refining / conversion, and uranium enrichment. Currently, our Center has completed its initial mission and is conducting decommissioning of facilities used for R&D, and R&D for decommissioning. Of the three main facilities of our Center, the refining conversion facility and the enrichment engineering facility have already begun dismantling equipment in the facilities. The uranium enrichment demonstration plant is in the process of applying for a decommissioning plan. This report provides an overview of the current status of our Center's decommissioning.

Decontamination performance evaluation of IF treatment technology and proof of IF production method

Ema, Akira; Kado, Kazumi; Suzuki, Kazuhiko*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 10(3), p.194 - 204, 2011/09

https://doi.org/10.3327/taesj.J10.026

This paper shows the investigation result of the reasonable IF treatment condition and the full-scale examination result by using this IF treatment condition. As a result, it could confirm 99% of the intermediate uranium fluoride in the cascade was removed for 60 days. Further, this paper shows the investigation result of the reasonable IF production condition and the full-scale examination result. As a result, it could be proved 3,355 kg-IF gas was produced.

Study on efficiency of dry decontamination technique by numerical method, 2 (Joint research)

Hyakutake, Toru*; Muto, Akinori*; Sasakura, Mariko*; Minowa, Hirotsugu*; Suzuki, Kazuhiko*; Yokoyama, Kaoru; Takahashi, Nobuo; Hata, Haruhi; Sugitsue, Noritake

JAEA-Research 2010-032, 32 Pages, 2010/10

JAEA-Research-2010-032.pdf:1.72MB

System decontamination has been generally carried out with the aim of reducing the amount of radioactive waste generated and minimizing human exposure to radiation released from nuclear fuel facilities. At the Ningyo-Toge Environmental Engineering Center, metal surfaces that are contaminated by uranium are dry decontaminated by using iodine heptafluoride (IF) as a system decontaminator. In this dry decontamination technique, a chemical reaction occurs between the uranium compound attached to the metal surface and IF. Only a few studies have been carried out on the decontamination efficiency, mechanism, level, etc. of dry decontamination techniques that use a decontamination gas. Therefore, the generalization of dry decontamination technique was assessed by a numerical method using decontamination data obtained at the Ningyo-Toge Environmental Engineering Center. A concrete analytical content is a depositing of Uranium Hexafluoride.

System chemical decontamination technology by the IF gas

Ema, Akira; Sugitsue, Noritake; Zaitsu, Tomohisa

Proceedings of 2007 ANS Topical Meeting on Decommissioning, Decontamination and Reutilization & Technology Expo (DD&R 2007) (CD-ROM), 3 Pages, 2007/09

When we decommission the equipments contaminated by the uranium, the dismantling process of the equipments and the disposal process of the radioactive waste will be carried out. However, costs of these processes will be very expensive. In order to minimize these costs, we have developed new decontamination technology to decontaminate below the clearance level without dismantling.

Recent status of decommissioning on uranium facilities and application of clearance

Daiten, Masaki

no journal, , 

Main equipment of the uranium refining and conversion facility had been dismantled from 2008 to 2013. The uranium enrichment pilot plant has been dismantled since 2014. Removal treatment of uranium residue in equipment of the uranium enrichment demonstration plant commenced from 2001. Based on the technological result of uranium removal treatment, removal treatment of uranium from the first operation unit commenced, and it will be completed in FY 2016. Measurement and evaluation of radioactivity concentrations of equipment for clearance level commenced in May 2013. After the radioactivity concentrations were confirmed, and the certificates were issued by Nuclear Regulation Authority, clearance objects were carried out from the uranium facility and aluminum materials were reused for the first time in Japan.

A Decontamination characteristic of the metal surface with uranium hexafluoride, 3; Evaluation of rational for decontamination technique

Nakayama, Takuya; Nomura, Mitsuo; Mita, Yutaka; Sugitsue, Noritake; Yonekawa, Hitoshi*; Bunbai, Misako*; Yaita, Yumi*; Murata, Eiichi*; Hosaka, Katsumi*

no journal, , 

For metal exposed to uranium hexafluoride, as a study of a method of reasonably decontaminating radioactive substances attached to a corrosion layer and a base material generated after opening to the atmosphere, removal using a simulated sample and an actual sample Based on the dyeing test results, evaluation of decontamination efficiency, secondary waste generation amount, etc. was carried out. As a result, it was confirmed that acidic functional water decontamination is totally superior to other dilution decontamination.

Discussion for the decommissioning DIQ in the main nuclear fuel cycle facilities such as reprocessing

Nakamura, Hironobu

no journal, , 

In accordance with the Japan-IAEA safeguards agreement, domestic operator has to declare the Design Information Questionnaire (DIQ) when the operator change the design information for the facilities of themself. In the IAEA, though they already released the procedure to make the DIQ from the construction to operation, unfortunately, they did not release the procedure from shutdown to decommission. So, the operator of all over the world is asking IAEA to release the common DIQ making guidelines as soon as possible. Therefore, IAEA hold the specialist meeting to make the DIQ guideline under decommissioning, and JAEA also attend to discuss the meeting because JAEA has several types of facilities and proposes subjects to be solve in order to revise the DIQ smoothly. In this paper, regarding the discussion for the decommissioning DIQ in the main nuclear fuel cycle facilities such as reprocessing, we present and propose about simple revise, clarification between stage of decommissioning and DIQ procedure, revision of nuclear material accountancy procedure and the termination of safeguards.

Decontamination method using acidic electrolyzed water for metals contaminated with radioactive materials

Nakayama, Takuya

no journal, , 

Facilities that have completed their missions of research activities or have become obsolete will be systematically decommissioned. The dismantling of these facilities is expected to generate a large amount of metal waste with contaminated surfaces. In particular, a large amount of ferrous metal wastes, such as carbon steel, are generated. In order to reduce the disposal cost of radioactive wastes, it is required to reduce the volume of radioactive wastes by efficient decontamination. Therefore, as a rational decontamination method, we evaluated decontamination characteristics using acidic electrolyzed water containing hypochlorous acid, diluted hydrochloric acid, and diluted sulfuric acid on a sample simulating a corrosion layer. As a result, it was found that acidic electrolyzed water is a decontamination solution with an appropriate balance between the effects of dissolving the base metal and dissolving and removing the corrosion layer.

Safeguards correspondence in post-operation phase at Uranium Enrichment Plant

Ishida, Tsuyoshi; Yamada, Shigeki*; Nakashima, Shinichi; Nakamura, Hironobu

no journal, ,