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Chvala’s “Sourdough” Refueling Method Envisions Reusing Spent Nuclear Fuel

Ondrej Chvala and Alex Wheeler.

Ondrej Chvala, left, and Alex Wheeler

Similar to how a baker can add ingredients to keep a sourdough starter active indefinitely, so too can spent nuclear fuel (SNF) be added to fuel salt in a molten salt reactor (MSR) by adding more fresh fuel salt. This in turn grows the in-core fuel salt volume and will eventually double the size of the original fuel salt, allowing to start another core with the excess fuel.

This “sourdough” method highlights how MSRs can effectively solve two problems at once: provide a source of clean, renewable energy while mitigating the need for disposing of high-level nuclear waste.

NE Research Assistant Professor Ondrej Chvala and doctoral student Alex Wheeler recently published a study in the Journal of Nuclear Engineering that set out to present an alternative to SNF storage, which is critical for public acceptance of nuclear power as a climate change solution. Using computer modeling, Chvala and Wheeler present a calculation methodology to show what the initial implementation of a “sourdough” style refueling in MSRs might look like.

“The ‘sourdough’ method has the potential to solve several problems at once,” said Chvala. “Reactor analysis codes need to be updated to include volume evolution when materials are fed to or removed from the reactor, but this initial calculation is a good indication that we can close the loop on spent nuclear fuel while making nuclear energy a bigger part of the climate solution.”

“The ‘sourdough’ strategy represents a fundamental rethinking of the nuclear fuel cycle, and we are at the forefront of it,” said Wheeler. “‘Sourdough’ refueling highlights unique features of molten salt reactors and uses them to their advantage. There is plenty more work ongoing to understand this method’s full potential.”

To be successful, the “sourdough” method depends on expanding the fleet of MSRs to accept each new batch of fuel. The growth rate can be adjusted by changing refuel enrichment. An additional economic advantage is that a new unit’s upfront cost is reduced since the sourdough doubling provides the first fuel load.