High temperatures and ionizing radiation create extremely corrosive environments inside nuclear reactors. To design long-lasting reactors, scientists must understand how radiation-induced chemical reactions impact structural materials. Chemists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Idaho National Laboratory recently performed experiments showing that radiation-induced reactions may help mitigate the corrosion of reactor metals in a new type of reactor cooled by molten salts. Their findings are published in the journal Physical Chemistry Chemical Physics.
"Molten salt reactors are an emerging technology for safer, scalable nuclear energy production. These advanced reactors can operate at higher, more efficient temperatures than traditional water-cooled reactor technologies while maintaining relatively ambient pressure," explained James Wishart, a distinguished chemist at Brookhaven Lab and leader of the research.
Unlike water-cooled reactors, molten salt reactors use a coolant made entirely of positively and negatively charged ions, which remain in a liquid state only at high temperatures. It's similar to melting table salt crystals until they flow without adding any other liquid.
The scientists were particularly concerned with tracking chromium, a frequent constituent of the metal alloys proposed for molten salt nuclear reactors. As chromium dissolves into the molten salt, some of its chemical forms can accelerate corrosion processes, compromising the structural integrity and performance of the reactor. The distribution of chromium ion oxidation states - how many electron vacancies these ions have available for chemical reactions - may be the factor that determines whether corrosion occurs.
Wishart and his collaborators used facilities to measure the rates and temperature dependencies of reactions of the two types of chromium ions with reactive species generated by radiation in molten salt. "Our analysis indicated that the net effect of radiation in the molten salt environment is to favor the conversion of corrosive Cr3+ to less-corrosive Cr2+," Wishart said.
This research was a product of the Molten Salts in Extreme Environments Energy Frontier Research Center established at Brookhaven National Laboratory by the DOE Office of Science in 2018 to explore the fundamental properties and potential applications of molten salts in nuclear environments.