Review of corrosion studies of metallic barrier in geological disposal conditions with respect to Belgian Supercontainer concept

Abstract

The Supercontainer design is the preferred option for the underground disposal of high level nuclear waste in Belgium. It consists of a carbon steel overpack surrounded by a thick concrete buffer. In this high alkaline environment and under normal conditions (without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is believed to result in very low uniform corrosion rates. The backbone of the RD&D strategy, which aims to provide confidence that the integrity of the overpack will be maintained at least during the thermal phase, is based on demonstrating that each localised corrosion mechanism (e.g. pitting corrosion, crevice corrosion and stress corrosion cracking), other than uniform corrosion, cannot take place under the high pH conditions prevailing within the Supercontainer (the 'exclusion principle'). This paper gives an overview of the status of the RD&D programme related to the anaerobic uniform corrosion of the carbon steel overpack. The outcome of the modelling efforts simulating the evolution of various parameters (temperature, pH, degree of saturation, corrosion potential and composition of aggressive species) that can potentially influence the corrosion processes, over geological timescales, is addressed.

Exploration of the effect of chloride ion concentration and temperature on pitting corrosion of carbon steel in saturated Ca(OH) 2 solution

“…The supercontainer (SC) is currently being studied as the reference design for the packaging of vitrified high-level radioactive waste (VHLW) and spent fuel (SF) in Belgium [2,3]. The SC design was developed based on the Contained Environment Concept (CEC), the basic idea of which is to encapsulate the carbon steel overpack in a tailor-made buffer that would establish and maintain a chemically benign environment around the overpack, with respect to corrosion, that is favorable in maintaining the overpack's integrity at least during the thermal phase of storage.…”

Review of corrosion interactions between different materials relevant to disposal of high-level nuclear waste

“…It is well established that the corrosion mechanism, rate, and product of CS strongly depend on the presence of oxygen in the environment 27,28 . For example, when aggressive species such as Cl − ions are below the threshold concentration, CS is likely to experience general corrosion under the anoxic condition dominant at the French and Belgian repository sites 20 . However, localized corrosion could still occur when CS is passivated by the increased pH during corrosion and the concentration of Cl − ions exceeds the threshold 29 .…”

“…As shown in Fig. 3, the SS canister 18 containing vitrified HLW will be surrounded by a CS overpack 19 with a wall thickness of 3 cm and then lined with ã 70 cm thick concrete buffer 20,21 . The alkaline environment conferred by the concrete can promote the formation of a stable passive film on the surface of the CS, leading to a low corrosion rate of the CS when aggressive species such as Cl − are absent.…”

Corrosion resistance of new powder metallurgy boron‐containing stainless steel in the nuclear repository environment

“…One of the options is its use for canisters for terrestrial burial of intermediate level radioactive waste (ILW), where the spent fuel is covered with concrete . Stainless steels may be applied as a top coating of a supercanister for the storage of high‐level radioactive waste (HLW) . Another option is burying the waste as a metal waste form (MWF) after melting the whole case incl.…”