Criticality accident

A criticality accident, or simply a criticality, is an accidental  nuclear fission chain reaction that goes out of control. These accidents are sometimes called critical excursions, critical power excursions, or divergent chain reactions. These reactions are the result of accidents involving fissile material (material that can undergo nuclear fission), and they can have very harmful results on the environment, as they let off large amounts of radiation.
During normal conditions, a critical reaction (a reaction that can keep itself going) only happens in safely guarded location. During a criticality, these reactions happen outside of these environments, or in a way that isn't safe. Criticality can be reached by solid materials (for example, metallic uranium), liquid materials, or by powder slurries. 

 Accident Types 
There are two primary types of criticality accident: 
 Process accidents, where controls in place to prevent an accident are breached.
 Reactor accidents, in which someone controlling the criticality in a normally safe environment makes a mistake, resulting in an accident. 

 Effects 
During a criticality, there are a handful of effects that have been commonly noticed. 

 Blue Glow 
During criticality events, there is often a blue glow. This is because the molecules during the reaction are very energetic, and release this energy by glowing.

 Heat Effects 
Some people say they have felt a 'heat wave' during a criticality accident. It is unknown if this is caused by their psychological reaction to the event, or if this is a physical result. It is frequently seen alongside the blue glow.

Category:Nuclear accidents