Study explores radiation-driven chromium chemistry in molten salt reactors

Study explores radiation-driven chromium chemistry in molten salt reactors
by Clarence Oxford
Los Angeles CA (SPX) Apr 03, 2025

High heat and ionizing radiation inside nuclear reactors generate intense chemical environments that threaten the durability of structural materials. To ensure the longevity of advanced reactor systems, researchers from the U.S. Department of Energy's Brookhaven National Laboratory and Idaho National Laboratory have investigated how radiation alters the chemistry of molten salts used as reactor coolants. Their work, published in Physical Chemistry Chemical Physics, reveals that certain radiation-driven chemical reactions may actually reduce corrosion risks.

"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 senior chemist at Brookhaven Lab and the study's principal investigator.

Unlike conventional reactors that rely on liquid water, molten salt reactors use ionic fluids composed entirely of charged particles that remain liquid only at high temperatures. This molten state is achieved by heating solid salts until they flow, without adding any other liquid medium.

To better predict material performance, scientists must understand how radiation affects the chemical composition of these molten salts, especially their interactions with alloy constituents like chromium.

"Chromium tends to be the easiest element to corrode from most alloys and will ultimately accumulate in the coolant of molten salt reactors," Wishart said.

Once dissolved in the salt, chromium can adopt different chemical forms. Some of these forms promote corrosion, potentially undermining the integrity of reactor materials. A key factor is the oxidation state of chromium ions, which determines their reactivity.

"The presence of dissolved trivalent chromium [Cr3+, with three electron vacancies] can accelerate corrosion in some cases, whereas divalent chromium [Cr2+, with just two vacancies] does not," Wishart said.

Because both Cr3+ and Cr2+ are stable in molten salts, researchers aimed to determine how these ions behave under radiation and what reaction products form as a result.

Brookhaven's unique facilities made this investigation possible. Scientists used the Laser Electron Accelerator Facility and the two-million-electron-volt Van de Graaff accelerator to initiate radiation-induced reactions and monitor them on timescales ranging from trillionths of a second to minutes.

By measuring how Cr3+ and Cr2+ ions react with radiolytically generated species at various temperatures, the team discovered a surprising trend. "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.

These findings suggest that, under the right conditions, radiation may play a role in stabilizing reactor materials by modulating the chemical environment in ways that limit corrosion.

Research Report:Kinetics of radiation-induced Cr(ii) and Cr(iii) redox chemistry in molten LiCl-KCl eutectic