Grizzly models the degradation due to normal operating conditions of nuclear power plant systems, structures, and components. The code also simulates the ability of degraded components to safely perform under a variety of conditions. Grizzly can be applied to a variety of components. However, its development focused initially on the embrittlement of reactor pressure vessels and concrete structures. Vessels can degrade and fracture due to irradiation and high temperatures, while concrete can degrade due to expansive alkali-silica reactions. Grizzly has capability to model the performance effect of these and other mechanisms.