• Observations of natural systems play an important role in the qualitative evaluation and enhancement of confidence, because such systems have evolved over extremely long time-scales.

A statement of confidence in the overall safety indicated by the performance-assessment results is part of the safety case and should include an evaluation of the arguments that were developed, in relation to the decision to be taken” (NEA, 1999a, pp. 9– 10).

Sidebar 5.1 discusses the safety case in the U.S. regulatory context.

2.3 Attributes of Adaptive Staging

A successful geologic repository program requires commitment to systematic learning, flexibility, reversibility, transparency, auditability, integrity, and responsiveness. These are the attributes that the committee uses to define Adaptive Staging. Although these attributes may exist separately in any staged project, successful application of Adaptive Staging requires that they be simultaneously satisfied both throughout each stage and in the decision-making process between stages.

  • Commitment to systematic learning. Commitment to systematic learning requires a structured program aimed at the acquisition and incorporation of new knowledge during the development of geologic repositories. Stages are designed specifically to increase the body of available knowledge, including scientific, technical, societal, institutional, and operational knowledge. Needs and questions are made as explicit as feasible at the outset of each stage. A central feature of Adaptive Staging is that it intentionally seeks, is open to, and learns from stakeholder input in all knowledge areas. The commitment to systematic learning is explicit in both the Adaptive Staging perspective and during program design. To realize the opportunities presented by a commitment to learning, it is also essential that appropriate institutional arrangements and attitudes be in place. Unless the scientific and management systems seek out and welcome alternative viewpoints, openly acknowledge errors and uncertainties, and implement negotiating strategies with local hosts and critics, learning will be minimal.

  • Flexibility. Flexibility is the capability and the willingness to reevaluate earlier decisions and redesign or change course if warranted by new information. Adaptive Staging is an iterative process that involves periodic reevaluation. Earlier decisions are questioned, or program changes are proposed, only if information gathered suggests the need for amending the next stage and thus altering the reference framework. Flexibility includes consideration of available technical and non-technical knowledge to determine the program direction while keeping options open.

  • Reversibility. Reversibility is the distinct option to abandon an earlier path and reverse the course of action to a previous stage if new information warrant. Because knowledge will accumulate as the project moves through stages, and project choices are made, the likelihood of reversal is expected to decrease as the project develops. Nevertheless, reversal must remain an option until the pro-



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