A fission process where the neutron production rate equals the neutron loss rate to absorption or leakage. A nuclear reactor is "critical" when it is operating
Centers for Disease Control and Prevention, Emergency Preparedness and Response, Radiation Emergencies, Radiation Dictionary, U.S. Department of Health and Human Services, Atlanta, GA, USA 2011. http://emergency.cdc.gov/radiation/glossary.asp, (Dzstr/ Rad Emr - Amer) {820}