“We did a genetic analysis and found a diverse population of mostly bacteria,” said Christopher Berry, the senior technical adviser of the Savannah River National Labortory.
The “white, stringlike” substance was first observed in October among old fuel assemblies submerged in the site’s L Area basin, where nuclear materials from foreign and domestic research reactors are stored and guarded.
Although the growth was deemed harmless, its ability to thrive and spread in such an unusual environment prompted a more detailed analysis.
“We were able to identify a large portion of the bacteria making up the cobwebs, but there were certainly some where the DNA sequencing came back as unknown,” Berry said.
Although rare, bacterial colonies have been observed in a few nuclear environments, including a Canadian reactor and at Three Mile Island in Pennsylvania, where a growth developed in the site’s spent fuel basin after its 1979 accident.
Scientists at SRS still have one more local mystery to solve.
“Right now we are trying to figure out what these bacteria are using for food,” Berry said. “In other words, what is their carbon source?”
Water in which spent fuel is stored is carefully filtered, treated and deionized to prevent anything that might contribute to corrosion – a perennial concern in nuclear waste storage.
If its food source can be identified and eliminated, the bacteria – and the cobwebs – might be more easily controlled, Berry said.
“We found no evidence it contributes to corrosion,” he said. “But visually, they want to get rid of it.”