Risk Dilution in a HLW Repository Risk Assessment

The geological deep disposal of Nuclear High Level Waste (HLW) is nowadays considered the most likely option to solve the problem of nuclear waste in the long term. In most of the countries that have developed nuclear civil programs, three options are considered as potential geological formations to host a repository: Granite, clay and salt, though other alternatives are not excluded. One of the requirements to get the approval from national authorities to operate such kind of facility is the demonstration of compliance with national regulations regarding post-closure safety. Post-closure safety criteria are based on the concept of risk in many countries, and the peak of the mean dose over time is the most widely used measure of risk. Uncertainty is a pervasive factor all over this process. We have to face model uncertainty, scenario uncertainty and parameter uncertainty. Not all our models are validated under all possible physical conditions and in some cases we could be omitting some relevant phenomena. Regarding scenarios, omitting some relevant scenario could be possible and estimating scenario probabilities is not an easy task. Finally, parameter uncertainty is a main issue, mostly when the origin of uncertainty is lack of knowledge instead of intrinsic variability. A trustworthy risk assessment should rely on an accurate assessment of all kinds of uncertainties. In this paper we address the issue of risk dilution in the risk assessment of a HLW repository. Risk dilution consists in getting a lower estimation of risk (peak of the mean dose over time), due to either wrong assessment of input parameter uncertain, or to inadequate treatment of events that could have a high impact on the dose but whose occurrence is stochastic and has a very limited action in time and/or space. The origin of this phenomenon is analysed in this work, its potential negative effects on a risk assessment and possible ways of dealing with it.

BOLADO LAVIN Ricardo; 

2006-11-03

European Commission - Joint Research Centre- Institute for Energy (JRC-IE)

JRC33359

https://publications.jrc.ec.europa.eu/repository/handle/JRC33359,