부산대학교 도서관

Engineered barriers including cementitious barriers are used at sites disposing or contaminated with low-level radioactive waste to enhance performance of the natural environment with respect to controlling the potential spread of contaminants. Drivers for using cementitious barriers include: high radionuclide inventory, radionuclide characteristics (e.g., long half-live, high mobility due to chemical form/speciation, waste matrix properties, shallow water table, and humid climate that provides water for leaching the waste). This document comprises the first in a series of reports being prepared for the Cementitious Barriers Partnership. The document is divided into two parts which provide a summary of: (1) existing experience in the assessment of performance of cementitious materials used for radioactive waste management and disposal and (2) sensitivity and uncertainty analysis approaches that have been applied for assessments. Each chapter is organized into five parts: Introduction, Regulatory Considerations, Specific Examples, Summary of Modeling Approaches and Conclusions and Needs. The objective of the report is to provide perspective on the state of the practice for conducting assessments for facilities involving cementitious barriers and to identify opportunities for improvements to the existing approaches. Examples are provided in two contexts: (1) performance assessments conducted for waste disposal facilities and (2) performance assessment-like analyses (e.g., risk assessments) conducted under other regulatory regimes. The introductory sections of each section provide a perspective on the purpose of performance assessments and different roles of cementitious materials for radioactive waste management. Significant experience with assessments of cementitious materials associated with radioactive waste disposal concepts exists in the US Department of Energy Complex and the commercial nuclear sector. Recently, the desire to close legacy facilities has created a need to assess the behavior of cementitious materials for applications in environmental remediation and decontamination and decommissioning (D&D) applications. The ability to assess the use and benefits of cementitious materials for these applications can significantly affect decisions related to cleanup activities. For example the need for costly remedial actions may not be necessary if existing or new cementitious barriers were adequately represented. The sections dealing with regulatory considerations include summaries of the different regulations that are relevant for various applications involving cementitious materials. A summary of regulatory guidance and/or policies pertaining to performance assessment of cementitious materials and sensitivity and uncertainty analyses is also provided in the following chapters. Numerous examples of specific applications are provided in each report. The examples are organized into traditional waste disposal applications (performance assessments), applications related to environmental remediation and D&D, and reactor and spent fuel related assessments. Sections that discuss specific facilities or sites contain: (1) descriptions of the role of the cementitious barriers or sensitivity/uncertainty analysis, (2) parameter assumptions and conceptual models, and (3) a relative discussion of the significance in the context of the assessment. Examples from both the U.S. Department of Energy Sites and the U.S. Nuclear Regulatory Commission are provided to illustrate the variety of applications and approaches that have been used. In many cases, minimal credit was taken for cementitious barriers. However, in some of those cases, benefits of being able to take credit for barriers were identified. The examples included: (1) disposal facilities (vaults, trenches, tank closures, cementitious waste forms and containers, etc.), (2) environmental remediation (old disposal facilities), (3) reactor and large structure decommissioning, and (4) spent fuel pools. These examples were selected to provide a perspective on the various needs, capabilities to model cementitious barriers, and use of sensitivity and uncertainty analysis and were not intended to include all cementitious barriers used in all low-level waste related PAs. The summary section in each report/chapter provides an overview of important considerations for the examples and compares and contrasts the different approaches that have been used. For example, specific time dependent physical processes (changes in hydraulic conductivity) and chemical processes (partitioning coefficients, and solubility coefficients) are identified and compared. The summary section also identifies key needs for future assessments. The Cementitious Barriers Partnership was established to address the key needs related to the use of cementitious barriers - waste forms, containment structures, physical stabilization fill materials.