This report summarizes work to date on a project for the U.S. Nuclear Regulatory Commission to develop guidelines for the chemical and material assessment of an existing structure considered for entombment. In addition, a rational means for performing a probabilistic calculation are addressed. This report does not include a summary of nondestructive evaluation (NDE) techniques applicable to existing cracks. That report will be written separately by Dr. N.J. Carino.The assessment is composed of a preliminary material assessment, followed by a probabilistic calculation of the service life. The material assessment will rely heavily on both the permeability of the intact concrete and the characterization of any existing cracks. The contribution of cracks to transport is considered independently from the intact concrete, and the bulk properties (intact concrete plus cracks) are estimtated by combining the two effects using a composite model. Another aspect of the condition assessment of the concrete barrier is the evaluation of nondestructive techniques (NDT) as candidates for characterizing existing cracks, and other transport pathways, in the entombment structure. This aspect will be addressed in a companion report.An important component of the effort to estimate the concrete material properties is the probability density function used to characterize the distribution in their expected values. The tail of the distribution has the greatest influence on the overall performance, and, therefore, it should receive attention in the analysis. A number of suitable distributions are considered for their use in characterizing various concrete material properties.
Citation: NIST Interagency/Internal Report (NISTIR) - 7026Report Number:
NIST Pub Series: NIST Interagency/Internal Report (NISTIR)
Pub Type: NIST Pubs
concrete, condition assessment, degradation, service life, transport