What happens if key safety systems fail?
The reactor vessel sits inside a larger containment vessel, which itself resides in an underground stainless steel-lined concrete pool of water. Shield covers and the reactor building itself reside above the reactor components. The reactor building will be a Seismic Category 1 reinforced concrete structure designed to withstand the effects of aircraft impact, environmental conditions, natural phenomena, and postulated credible accidents and threats.
The reduced amount of fuel, inherent safety features and natural physics of the reactor’s design eliminate the possibility of fuel damage in all design-basis events (events that a nuclear facility must be designed and built to withstand). For “beyond design-basis” events (accident sequences that were not fully considered in the design process because they were judged to be too unlikely -- on the order of once in every 10 billion years), the radiation from fuel damage would not exceed U.S. EPA established limits at the plant site boundary.