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certainty, conducted in RTDC-1 as Work Package 1.2 (WP1.2). This initial review is summarised in
Section 2.
RTDC-2 is organised in three work packages:
WP2.1 is researching key drivers and methodologies for the treatment of uncertainty, addressing
regulatory compliance, the communication of uncertainty, approaches to system PA, and techniques
for sensitivity analysis.
WP2.2 is proceeding in parallel with WP2.1 and is testing and developing the framework outlined
in WP1.2 by undertaking a series of exercises to provide examples of uncertainty treatment
from different European programmes at different stages of development. The work is divided
into tasks that consider the main types of uncertainties (scenario, model, parameter), the
treatment of spatial variability, and the development of probabilistic safety assessment tools.
WP2.3 is a synthesis task pulling together the WP1.2 review, and research on the treatment of
uncertainty under WP2.1 and the testing and development work under WP2.2 to arrive at final
guidance on approaches for the treatment of uncertainty during PA and safety case development
that contains state-of-the-art examples from RTDC-2 for a range of key areas.
Most of this work is still underway, so we focus here on the outcome of the WP1.2 review, a brief
description of the work in progress, and, in Section 4, a longer summary of the one complete task in
RTDC-2 on the regulatory evaluation of uncertainty.
2. WP1.2 Initial Review of the Treatment of Uncertainty
The aim of WP1.2 was to develop a document that synthesises the state-of-the-art at the beginning
of the project, providing examples on approaches to the treatment of different types of uncertainty
at different stages of safety case development and highlighting areas where further development
would be most helpful. Information on the treatment of uncertainties was gathered from PAMINA
participants and several other organisations using a questionnaire, and via a limited wider review of
the literature. The questionnaire responses obtained represent 16 disposal programmes in 13 countries,
including all of the countries with advanced programmes to implement geological disposal,
allowing the review to give wide coverage of global activity. Selected results from the review are
given here. A more complete summary is provided in [1].
2.1 Types of Uncertainties Considered in PA
There is consensus on both how uncertainties considered in PAs should be classified and the nature
of uncertainties, although this is masked by variations in terminology and differences in the way
uncertainties are treated in programmes. Uncertainties in PAs are generally classified as:
1. Uncertainties arising from an incomplete knowledge or lack of understanding of the behaviour
of engineered systems, physical processes, site characteristics and their representation using
simplified models and computer codes. This type of uncertainty is often called “model” uncertainty.
It includes uncertainties that arise from the modelling process, including assumptions associated
with the reduction of complex “process” models to simplified or stylised conceptual
models for PA purposes, assumptions associated with the representation of conceptual models
in mathematical form, and the inexact implementation of mathematical models in numerical
form and in computer codes.
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