Explain the practical implication of the departure from nucleate boiling ratio (DNBR) in reactor core thermal-hydraulics.

The Departure from Nucleate Boiling Ratio (DNBR) is a critical parameter in reactor core thermal-hydraulics, indicating how close the heat flux on the surface of a fuel rod is to the point where nucleate boiling transitions to film boiling. Nucleate boiling is a highly efficient heat transfer regime where bubbles form and detach from the fuel rod surface, effectively removing heat. Film boiling, on the other hand, is a much less efficient regime where a layer of vapor insulates the fuel rod surface from the coolant, drastically reducing heat transfer. The D....