​ Grizzly is a code for modeling degradation of nuclear power plant systems, structures, and components due to exposure to normal operating conditions.  Grizzly models both the degradation process, as well as the ability of degraded components to safely perform their intended functions under a variety of conditions. Grizzly is intended to be applied to a variety of components, but development has focused initially on two main areas: embrittlement of reactor pressure vessels, and degradation of concrete structures.​

Reactor pressure vessels (RPVs) contain populations of flaws introduced during the manufacturing process that could potentially serve as fracture nucleation sites during normal or abnormal operating conditions. Embrittlement caused by exposure to irradiation and elevated temperatures makes RPVs more susceptible to fracture over time. Grizzly has capabilities for performing engineering fracture assessments of RPVs. Work is underway to develop models of the evolution of the microstructure and engineering properties of RPV for improved prediction of material embrittlement.

Nuclear concrete structures can experience degradation due to a variety of mechanisms. One of particular concern is expansive alkali-silica reactions (ASR). Grizzly has coupled physics models to predict the evolution of ASR and its effects on the mechanical response of concrete structures.

Grizzly prediction of stress and temperature in a reactor pressure vessel subjected to a pressurized thermal shock scenario:


Representative Grizzly prediction of the ductile-brittle transition temperature shift (in degrees F), a measure of the extent of embrittlement in RPV steel using the EONY model.