dateOfFirstCriticality

Given a predicate that represents a relationship or action between entities, generate a one-sentence description explaining its meaning.  
# Instructions
Focus on describing the relationship, not the entities themselves. 
# Response Format
Begin the description with \' Indicates...\'

Predicate: dateOfFirstCriticality

Indicates the date on which a nuclear reactor or system first achieved a self-sustaining nuclear chain reaction (first became critical).