Molten salt reactors will create electricity more safely and efficiently
By Leigh Thomas | August 31, 2020
He is helping lead a team producing a Molten Salt Thermodynamic Database that will be used by a number of companies and regulators around the world endeavoring to develop molten salt reactors that would be safer, smaller and more economical than the current fleet of water-cooled reactors.
“To do that, they need a database of thermodynamic values for the salts in order to accurately calculate factors such as melting point of the complex salt as its composition changes in the reactor, or whether the salt will significantly corrode the reactor vessel and piping,” Besmann said.
Today’s water-cooled reactors use nuclear fuel in the form of ceramic uranium pellets about one-half inch tall to create power. The pellets are stacked in tubes approximately 15 to 18 feet tall, with several thousand making up the core of the reactor. When the reactor is turned on, the uranium creates heat to boil water and make steam that runs a turbine to generate electricity.
In a different approach, molten salt reactors use a salt such as sodium chloride combined with uranium chloride, which is heated above its melting point, forming a liquid that can be pumped around a loop. As the salt flows through the loop, it enters a region where the configuration is such that uranium can undergo a nuclear fission chain reaction and heat is generated. Then, in another part of the loop, that heat is transferred to a second fluid which goes on to make electricity in the usual manner.
According to Besmann, molten salt reactors require less equipment to maintain safety and can be made smaller in size. Traditional, large reactors must be cooled even when turned off, otherwise the fuel overheats and can melt, damaging the reactor. In a molten salt reactor the fuel is already melted, and a smaller reactor allows excess heat to escape through natural processes – preventing dangerous overheating.
Molten salt reactors are attractive to utility companies, such as Dominion Energy, as they look to add or replace power sources. At one-third the size of traditional nuclear reactors, they are simpler and cheaper to build. As a region grows and the need for power increases, utilities can add power capability incrementally and risk less capital, ultimately benefiting the consumer.
As molten salt reactor technology develops, it is important to know factors such as the melting point of various salt compositions. This allows the operator to maintain temperatures in a useful range, yet avoids exceeding temperatures that the metal constructing the reactor can withstand. As the reactor operates, additional elements are created as a result of the nuclear fission reaction, with the uranium splitting apart into other atoms.
“The introduction of other elements in the reactor changes its chemistry. A question is, is it going to create solids? Corrode piping? We need to understand thermodynamics of these elements in the salts, and include those in the database so we can predict their behavior. That’s our job,” Besmann said.
The U.S. Department of Energy tasked Besmann and his team with developing a database of chemical thermodynamic values that can be used to calculate the behavior of the salt. The team has completed the first version of the database containing values for 60 different compounds and will continue expanding it to include additional elements and compounds that are important.
Besmann is a professor and Smart State Chair in the University of South Carolina College of Engineering and Computing. His research interests are related to thermochemical experiment and modeling for nuclear fuel development and in-reactor behavior, as well as development of advanced nuclear waste forms.