Thermal Hydraulics: Heat, Water, Nuclear Power and Safety

Scott Krepel
Reactor System Engineer

One of the most important safety questions in a nuclear power plant is: Can you cool the very hot nuclear fuel in an accident when normal cooling is disrupted? The scientific field best equipped to answer this question is called “thermal hydraulics.”

bwrThe first part of the term, “thermal,” relates to heat transfer, such as the movement of heat from the burner on a stove to the water in a pot via the metal of the pot. The second part, “hydraulic,” relates to the flow of a fluid such as water. The combination, “thermal hydraulics,” can be applied to systems where both the flow of fluid and the transfer of heat are important – such as a nuclear power plant.

I work in the NRC’s Office of Nuclear Regulatory Research as part of a team dedicated to expanding our understanding of thermal hydraulics and applying that understanding in nuclear power plant safety. Over time, we’ve put much effort into incorporating existing knowledge into the NRC’s thermal hydraulics computer simulation program, TRACE. This program allows NRC staff to construct computer models of the cooling systems of a nuclear power plant and then simulate accidents such as pipe breaks (but not wildly improbable events such as the considerable destruction caused near the end of a typical superhero action movie).

TRACE is constantly being pushed to become more accurate, reliable and versatile. Universities and test facilities around the world are conducting experiments and accident simulations to collect real-world data that can be used to determine TRACE’s ability to accurately predict specific phenomena. We use the outcomes to update the program as needed to make it more accurate and to better capture certain phenomena.

Sometimes, new safety issues may result in further investigation of certain scenarios and further evolution of TRACE. Ultimately, the goal of this work within the research arm of the NRC is to continuously expand our understanding of situations which may impact the cooling of the nuclear fuel. This knowledge can then be used to ensure that the public and the environment are protected in the unlikely event of an accident at an U.S. nuclear power plant.