In-service inspection programs have the primary goal of ensuring that the NPP structures have sufficient structural margins to continue to perform in a reli­able and safe manner.86,87 A secondary goal is to identify environmental stressors or aging factor effects before they reach sufficient intensity to poten­tially degrade structural components. Routine obser­vation, general visual inspections, leakage-rate tests, and destructive and nondestructive examinations are techniques available to identify areas of NPPs that have experienced degradation.

Determination of the existing performance char­acteristics and extent and causes of any observed distress is accomplished through a structural condi­tion assessment that routinely initiates with a general visual inspection to identify suspect areas followed by application of destructive or nondestructive exami­nations to quantify the extent and significance of any observed degradation. Basic components of a condi­tion assessment include (1) a review of ‘as-built’ drawings and other information pertaining to the original design and construction so that information, such as accessibility and position and orientation of embedded steel reinforcing and plates in concrete, is known prior to the site visit; (2) detailed visual exam­ination of structure to document easily obtained information on instances that can result from or lead to structural distress (e. g., crack mapping); (3) determination of the need for additional surveys or application of destructive or nondestructive test­ing methods; (4) analysis of results; and (5) prepara­tion of a report presenting conclusions and recommendations. More detailed information on guidelines on conduct of surveys of existing civil engineering buildings is available.88-91

Some general guidance on assessment of NPP deg­radation is also available.92-95 However, NPP rein­forced concrete structures present special challenges for development ofacceptance criteria because oftheir massive size, limited accessibility in certain areas, sto­chastic nature of past and future loads, randomness in strength, uncertainty in material changes due to aging and possibly degradation, and somewhat qualitative nature of some nondestructive evaluation techniques. Improved guidelines and criteria to aid in the inter­pretation of condition assessment results, including development of probability-based degradation accep­tance limits, are required. (Some information on probability-based crack acceptance limits for beams and shear walls considering loss of steel area and concrete spalling is available.96)