Development of a new corrosion mitigation technology using nanobubbles toward corrosion mitigation in PCV system under the influence of α/β/γ-rays radiolysis (Contract research). FY2022 Nuclear Energy Science & Technology and Human Resource Development Project

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 FY2022. Among the adopted proposals in FY2020, this report summarizes the research results of the 'Development of a new corrosion mitigation technology using nanobubbles toward corrosion mitigation in PCV system under the influence of α/β/γ-rays radiolysis' conducted from FY2020 to FY2022. The present study aims to corrosion, which is considered to be an important factor in the aging degradation of confinement functions (PCV, negative pressure maintenance system, etc.) during the fuel debris removal process. If the chemical species (especially H₂O₂) generated by radiolysis become locally concentrated in the areas where short-range α- and β-radiation emitting nuclides come into contact, the corrosion of steels may be greatly accelerated in those areas. In contrast, there was a lack of knowledge on corrosion evaluation considering α/β radiolysis. In view of this background, the following research results were obtained in this study. (1) A radiolysis analysis model covering the effects of α-, β-, and γ-rays was developed, (2) Systematic corrosion rate data were obtained from electrochemical tests (hot tests) using α- and β-ray emitting nuclides and simulated environmental corrosion tests under cold conditions, (3) Based on the above results, recommendations were made from the viewpoint of corrosion resistance for the selection of materials for new facilities to be attached to or inserted into the PCV system. The knowledge obtained in this study that contributes to the evaluation of corrosion rates under the influence of α- and β-rays has expanded the existing database on corrosion under radiation, which dealt only with γ-rays, (4) The introduction of inert gas nanobubbles was proposed as a corrosion inhibition technique in PCV systems, and basic knowledge was obtained regarding its effectiveness and limitations. (J.P.N.)