Salt Disposal of Heat-Generating Nuclear Waste

3 PERFORMANCE ANALYSIS FOR HLW
DISPOSAL IN SALT
The information presented in Section 2 summarizes an understanding of and
expectations for the thermal, hydrologic, mechanical, and chemical behavior of
salt as a disposal medium for HLW. This section discusses the development of a
performance-based, directed research program using the PA methodology shown
in Figure 9 as a tool.
The PA methodology shown in Figure 9 does not simply encompass
demonstrations of repository performance and regulatory compliance, which is a
more traditional definition of PA. In early stages of repository development, as
disposal in a particular geologic medium or with a particular design concept is
being considered, the methodology includes analyses that inform the decision
maker about what is important for repository performance and what, if any, “data
gaps” would need to be filled. Thus, this methodology is the basis for a directed
science program that may lead to the development of a repository for HLW.
These principles have been applied to several very different disposal concepts that
advanced to licensing: WIPP, Yucca Mountain Project, and Greater Confinement
Disposal (Cochran and Price 2006). Although these are dissimilar settings and
have different controlling regulations, the performance assessment methodology
integrates the same key elements.
The first step, Performance Goals, establishes overarching boundary conditions,
which govern the framework for subsequent strategic choices (Figure 9). The
boundary conditions include national and international law and regulatory
requirements. The second step, Characterize System, develops the strategic
choices that are intended to meet the performance goals. These include the
geologic formation, the waste inventory and the concept of disposal. At the time
of this report, regulatory performance goals specific to a salt repository for HLW
are not available, but one can envision goals similar to those that exist for other
repository programs, including the complete containment approach adopted by
Germany (Rothfuchs et al. 2010). The second step becomes increasingly
important as the repository project moves from concept to implementation and the
performance of a particular system must be established. The third step, Identify
Scenarios for Analysis, involves the systematic process of evaluating the FEPs
associated with the particular site, the concept of operation, and the HLW waste
inventory.
The next step, Performance Assessment, involves development and
implementation of conceptual and mathematical models, and numerical models
incorporated into simulation software. One can use the output from this step to
inform decisions about compliance with performance goals (upper right hand side
of Figure 9) or to inform decisions about a directed science program (lower left
hand side of Figure 9). The latter is the objective of this section. Based on
experience in the U.S. and collaborations with international peers (e.g., Belgium
and Germany), the content of this section follows the process shown in Figure 9 at
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