Tritium removal of heavy water system and helium system in FUGEN

Takiya, Hiroaki; Kadowaki, Haruhiko; Matsushima, Akira; Matsuo, Hidehiko; Ishiyama, Masahiro; Aratani, Kenta; Tezuka, Masashi

JAEA-Technology 2020-001, 76 Pages, 2020/05

JAEA-Technology-2020-001.pdf:6.06MB

Advanced Thermal Reactor (ATR) FUGEN was operated for about 25 years, and now has been proceeding decommissioning after the approval of the decommissioning plan in Feb. 2008. The reactor, heavy water system and helium system are contaminated by tritium because of neutron absorption of heavy water, which is a moderator. Before dismantling these facilities, it is necessary to remove tritium from them for not only reducing the amount of tritium released to surrounding environment and the risk of internal exposure by tritium but also ensuring the workability. In first phase of decommissioning (Heavy Water and Other system Decontamination Period), tritium decontamination of the reactor, heavy water system and helium system started in 2008 and completed in 2018. This report shows the results of tritium decontamination of the reactor, heavy water system and helium system.

Result of dismantlement on the turbine systems in FUGEN

Aratani, Kenta; Takiya, Hiroaki; Koda, Yuya; Ishiyama, Masahiro; Tezuka, Masashi; Mizui, Hiroyuki

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 5 Pages, 2019/05

https://doi.org/10.1299/jsmeicone.2019.27.1548

The prototype advanced thermal reactor FUGEN is the heavy water-moderated, boiling light water-cooled, pressure tube-type reactor, and has progressing the decommissioning since 2008. The most of facilities such as turbine system have the system structure and the operating conditions similar to those of BWR, although FUGEN has the characteristic structure of reactor core and the heavy water treatment facilities. In Japan, the knowledge and findings from FUGEN decommissioning activities are very important and valuable to perform BWR decommissioning in future, because the decommissioning of FUGEN is research and development as the first decommissioning of real-scale reactor. In the first phase of FUGEN decommissioning activities, the dismantlement project of reactor core cooling system started. By 2017, the low-level contaminated equipment such as the condensers of turbine system and the main-steam pipes of main-steam system was dismantled, and the management data was accumulated. The knowledge and findings from the 10 years of dismantlement experience will be reflected to the future dismantlement of higher contaminated facilities.

Pipe cutting method at high radiation area in FUGEN

Takiya, Hiroaki; Ishiyama, Masahiro; Tezuka, Masashi; Kitayama, Naoki

Proceedings of International Conference on Dismantling Challenges; Industrial Reality, Prospects and Feedback Experience (DEM 2018) (Internet), 8 Pages, 2018/10

In FUGEN, we had isolated the reactor core by cutting pipes of the periphery systems (e.g. reactor cooling system, heavy water system, and helium system) between 2015 and 2017, as preparation for dismantling the reactor core and taking some samples from the reactor core structures. There are three issues to be solved at this isolation work; (1) to shorten the working time at high radiation area which is 1-5mSv/h at air and 10mSv/h at contact, (2) to prevent tritium spreading to working area at cutting work because tritium air is existing with 20-30Bq/cm inside of the heavy water system and helium system, and (3) to minimize the influence of contaminated fume for the accurate radioactivity evaluation of reactor core structure. In this study, considering these problems, we discussed the method for cutting the pipes of heavy water system and helium system at the high radiation area and carried out the pipe cutting in the way.