Some of the high-level waste containment structures were exposed to very hot waste (e.g., 300° - 600° F) early in their lives. At these temperatures, concrete loses its strength and stiffness (Reference 12). Thermal creep also is a concern. Therefore, the concrete components of the high-level waste containment structures may need to be evaluated with lower allowable stress and stiffness values. All such potential degradation effects need to be considered in performing structural assessments of the high-level waste containments (Reference 13).