Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc. (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*

JAEA-Review 2025-008, 134 Pages, 2025/09

JAEA-Review-2025-008.pdf:10.0MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc." conducted from FY2021 to FY2023. Since the final year of this proposal was FY2023, the results for 3 fiscal years were summarized. In order to retrieve fuel debris, it is necessary to shut off the water at the bottom of the dry well and repair it in order to control the PCV water level. Therefore, in this study, we evaluated a construction method of stopping the water of the jet deflector with an improved geopolymer and repairing the lower part of the dry well by experiments and simulations. In addition, after understanding the properties of the fuel debris coated with the geopolymer, the long-term life of the waste body was evaluated. As a result, it was predicted that by utilizing geopolymers, it is possible to stop water and repair the lower part of the PCV in consideration of steps from construction to waste management.

Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc. (Contract research); FY2021 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*

JAEA-Review 2022-062, 121 Pages, 2023/03

JAEA-Review-2022-062.pdf:4.78MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc." conducted in FY2021. The present study aims to propose a construction method to stop jet deflectors by improved geopolymer and ultra-heavy muddy water, and to repair the lower part of the dry well. In addition, in order to increase the options for on-site construction in unknown situations such as deposition conditions, we will examine a wide range of construction outside the pedestal, and evaluate the feasibility of the construction method by the latest thermal flow simulation method. When widely constructed, fuel debris and deposits discharged out of the pedestal are coated with water stop and repair materials and become waste ...

The Accelerated corrosion of carbon steel in air-solution alternating condition

Otani, Kyohei; Tsukada, Takashi; Terakado, Hiroshi*; Ebata, Koei*; Ueno, Fumiyoshi

no journal, , 

Inner components of the primary containment vessels (PCVs) in Fukushima Daiichi Nuclear Power Station was observed by remote-controlled robots and the observation showed that carbon steels of the PCVs wall above the contaminated water level was exposed to an air-solution alternating condition. Previous studies have reported that the corrosion rate of carbon steel is accelerated in case of the steel with thin water film exposed in air under the dry/wet condition. This suggests that the corrosion rate of carbon steel will be accelerated in the air-solution alternating condition. However, the corrosion rate of the steel on the corrosion tests which simulated the air-solution alternating condition has not been clarified. In the present study, a novel corrosion test of carbon steel which simulated the air-solution alternating condition was carried out. In order to simulate the alternating condition in the novel corrosion test, the carbon steel was alternately exposed to air and solution by rotating in a water tank which was not completely filled with solution. The surface observations showed that the rust layer formed on the steel after the tests in the alternating condition was thicker than that of the steel rotated always in solution. The mass loss measurements showed that the corrosion rate of carbon steel in the alternating condition was more than three times larger than that of the steel rotated always in solution. A thin water film was confirmed on the steel when the specimen exposed to the air during the tests. It has been reported that the mass transfer of dissolved oxygen to the carbon steel surface is accelerated in case of the carbon steel covered by a thin water film and corrosion of carbon steel is accelerated by the acceleration of oxygen reduction reaction (cathodic reaction). This suggests that the accelerated corrosion of the steel in the alternating condition would be caused by the thin water film on the steel during the tests.

Corrosion mechanisms of carbon steel in the simulated air/solution interface

Otani, Kyohei; Kato, Chiaki

no journal, , 

Cooling water is circulated and injected into the containment vessel (PCV) of Fukushima Daiichi Nuclear Power Station (1F) Units 1-3, and nitrogen gas is injected and filled to prevent hydrogen explosion and to control corrosion of steel materials. In order to maintain the integrity of the PCV facilities over a long period of time until the decommissioning of the reactors, it is necessary to predict the corrosion behavior of carbon steel, which is the main structural material, and in particular to study the factors that may accelerate corrosion. From the internal investigation of the PCV, it was confirmed that carbon steel, which is the material inside the PCV, is exposed to an environment in which the gas and liquid environments alternate near the air/solution interface (Air/solution alternating environment). It has been reported that metallic materials are covered with a thin liquid film near the air/solution interface, and that the corrosion rate of steel is accelerated when there is a thin water film on the steel surface compared to that in solutions. In this presentation, the corrosion test of carbon steel was conducted using a rotating corrosion test apparatus to simulate the air/solution alternating environment inside the 1F PCV, and the corrosion rate and corrosion mechanism of carbon steel obtained from the results of mass measurement, observation and analysis will be presented.