Abstract
Abstract. Regulatory review of the licence application for construction and operation of a spent fuel repository at the Forsmark site in Sweden involves detailed assessment of both expected and hypothetical failure modes of the copper canister. The copper canister, which is supported by the bentonite buffer and the surrounding crystalline rock in the KBS-3 concept, is expected to provide complete containment of radioactive elements for very long timescales. Detailed assessment shows that there is a small probability on such timescales of canister failure due to corrosion following loss of buffer as well as mechanical failure due to large earthquakes. During the regulatory review process, it was proposed that canisters might also fail due to: (i) corrosion in anoxic oxygen gas free water, (ii) pitting corrosion, (iii) stress corrosion cracking, (iv) creep brittle failure, (v) hydrogen embrittlement. We here provisionally accept a number of alternative assumptions related to these processes as a basis for what-if analysis of their implications. The focus is not to determine the merit or to estimate probability of these cases, but rather to explore their potential significance in the context of the available knowledge about the repository environment. Simplified estimates are made of the consequences in terms of number and timing of canister failures as well as radiological impact. It is judged that poor creep ductility of copper would have larger potential consequences compared to localised corrosion phenomena. Potential corrosion failures are expected to be associated with the small fraction of deposition holes that are most extensively exposed to corrodants.
Highlights
The purpose of geological disposal of spent nuclear fuel and other radioactive wastes is to ensure long-term protection of people and the environment from the hazards such wastes represent
Strömberg et al.: Exploratory what-if analysis of some debated canister failure modes paper, we address the failure modes of the copper canister, and in particular assessment of alternative failure modes that have been proposed as causes for “early” failures (e.g. Pettersson, 2012; Szakálos and Seetharaman, 2012)
We address the following postulated failure modes of the copper canister, by examining the potential implications of alternative assumptions: (i) corrosion caused by anoxic water, (ii) pitting corrosion, (iii) stress corrosion cracking, (iv) creep brittle failure, and (v) hydrogen embrittlement
Summary
The purpose of geological disposal of spent nuclear fuel and other radioactive wastes is to ensure long-term protection of people and the environment from the hazards such wastes represent. Risks for future generations living in close proximity to a sealed disposal facility should be very small. These objectives are achieved by selecting a site with favorable rock conditions, by using an effective engineered barrier system, and by constructing and operating the repository facility in ways that facilitate long-term safety. In 2011, the Swedish Nuclear Fuel and Waste Management Company (SKB) submitted a licence application for construction and operation of a spent fuel repository at the Forsmark site in Sweden. The application is based on the KBS-3 concept consisting of three primary barriers; the copper canister, the bentonite buffer and the crystalline bedrock at about 500 m depth
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