DNBR

Departure from Nucleate Boiling Ratio

A safety parameter used in nuclear reactor thermal-hydraulic analysis to ensure adequate cooling of fuel rods during normal operation and anticipated transients. DNBR quantifies the margin between actual heat flux and the critical heat flux that would cause transition from efficient nucleate boiling to less effective film boiling preventing fuel damage by ensuring sufficient cooling under various operating conditions and maintaining thermal safety margins in nuclear power plants.