heightened sensitivity to the committee’s statements concerning the Yucca Mountain Project. The committee is not charged to participate in this decision and has not considered the merits of the choice at hand. However, the statement of task does require the committee to examine the concept of staging in principle and then in application to the Yucca Mountain Project. The committee has endeavored to ensure that the results of its deliberations will be valuable and applicable no matter what decision is made on the Yucca Mountain site.

The main points of this progress report are summarized as follows.

  • Adaptive staging is defined as a process where the development of a geologic repository for high-level waste is divided into stages that are separated by explicit decision points. Decision points provide the opportunity to evaluate obtained results and to decide how to proceed to the next stage. In fact, any subsequent stage is predicated upon the outcome of previous ones. Decision points also allow for program improvement with respect to, for instance, safety, costs, and schedule. Under adaptive staging, the repository implementer, at each decision point between stages, would:

  1. analyze knowledge gathered from previous stages;

  2. take into account all relevant options for the next stage, including explicit consideration of reversibility;5,6

  3. evaluate and update the safety case;7

  4. decide on the next stage based on the above set of actions.

All of the above actions would incorporate input from stakeholders8 who would also receive feedback on the decisions taken. The committee is still in the process of discussing the role of stakeholders at decision points. In other words, adaptive staging is a cautious, deliberate, decision and management process that involves continuous learning and is also transparent and reversible.

  • The overarching attribute of adaptive staging is that it aims to increase repository safety and to reduce uncertainties through systematic incremental learning. The safety case is at the heart of adaptive staging and drives the identification and choice of options at each stage. Commitment to systematic learning, flexibility, auditability, transparency, integrity, and responsiveness underlie the overarching safety attribute.


Reversibility denotes the possibility of reversing one or a series of steps in repository development at any stage of the program. However, if no evidence questioning safety emerges as the program proceeds, decisions become firmer and reversal on technical ground becomes less likely. See section 1 in Attachment A for details.


Reversibility is discussed in this report as part of the adaptive staging general concept. This discussion should not be interpreted as a recommendation about the Yucca Mountain Project.


A safety case is a collection of arguments, at a given stage of repository development, in support of the long-term safety of the repository. A safety case comprises the findings of a safety assessment and a statement of confidence in these findings. It acknowledges the existence of any unresolved issues and provides guidance for work to resolve these issues in future development stages (NEA, 1999c). DOE adopted a very similar definition of safety case in the framework of the Yucca Mountain Project (DOE, 2000).


As defined by DOE, a stakeholder is a person or organization with an interest in or affected by DOE actions. This includes representatives from Federal, state, tribal, or local agencies; members of Congress or state legislatures; unions, educational groups, environmental groups, industrial groups; and members of the general public (DOE, 2002a).

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