Nuclear criticality accidents have killed, but these accidents don’t happen often because when they do occur, the results have historically proven disastrous; regulations, training, and procedural safeguards have all intensified in the wake of high-profile, fatal events around the world. Accidental criticality is a hazard unique to facilities where fissionable materials are handled or stored, such as nuclear fuel manufacturing and processing facilities. The Nuclear Regulatory Commission characterizes these events as “uncontrolled nuclear fission chain reactions.” So, that’s what we’re talking about, and unexpected, unplanned nuclear episode that poses risk to human health and wellbeing proportionate to the size of event and proximity of those exposed.