Aging of fuel-containing materials (fuel debris) in the Chornobyl (Chernobyl) Nuclear Power Plant and its implication for the decommissioning of the Fukushima Daiichi Nuclear Power Station

Nuclear fuel debris, the debris formed after the severe accidents of nuclear power plants, is a complex material containing a wide range of elements, compounds, and radiation. This complexity renders all the stages of the treatment of nuclear fuel debris (including removal, storage, and (interim- and final) disposal) extremely difficult and troublesome in the technical context. The whole treatment of nuclear fuel debris is also an extremely long-term process for tens of thousands of years. During this extremely long period of time, the aging of nuclear fuel debris is an unavoidable but critical issue, as the aging could change the physical/chemical properties of the fuel debris and, consequently, could potentially affect the strategy and planning of the treatment of the fuel debris. This, needless to say, applies to the decommissioning of the damaged reactors of the Fukushima Daiichi Nuclear Power Station (1F). In order to estimate the potential effects of aging on the nuclear fuel debris remaining in the damaged 1F reactors, the severe accident at the Chornobyl (Chernobyl) Nuclear Power Plant Unit 4 (ChNPP-4) is a unique and valuable source of information on the aging of materials containing nuclear fuels. Given this background, this review aims at collecting and summarizing the knowledge and information about the aging of materials containing nuclear fuels (fuel-containing materials, FCM) formed as a result of the accident at ChNPP-4 in the light of the decommissioning of 1F. The aging on FCM at ChNPP-4 is classified according to its origin (physical, chemical, or biological) and surrounding conditions (temperature, humidity, and radiation). Based on this classification and the knowledge/information collected from ChNPP-4, the potential effects of aging on the nuclear fuel debris at 1F are discussed.