Citing safety concerns, the US Department of Energy has formally abandoned a technology it had once counted on to vastly reduce the amount of liquid HLW defence wastes requiring vitrification. DoE hopes to choose an alternative process by autumn.
The flawed process, known as “in-tank precipitation” (ITP), injected sodium tetraphenylborate into a 1.3 million gallon processing tank containing liquid HLW. This was supposed to convert caesium in the liquid HLW into a chemical that would fall to the bottom of the tank. The precipitate would then have been filtered out and sent to another facility where it would have been washed with monosodium titanate, to reduce nitrite concentrations, and finally sent to a vitrification plant at the Savannah River Site in South Carolina.
But tests showed the ITP separation process created potentially explosive benzene gas. Now, DoE hopes an alternative process can be developed to separate out ceasium from 35 million gallons of liquid HLW stored in 49 underground storage tanks at Savannah River. DoE plans call for converting the most radioactive material into about 6000 glass logs which would be placed in canisters for eventual burial. If all 35 million gallons of liquid HLW had to be vitrified, the costs would be exorbitant. That option, for example, would require an additional 118 000 canisters at an estimated cost of more than $75 billion.
Over the past year, DoE evaluated 142 alternative separation technologies, paring its options down to three. Among them is a scaled-back, small-tank version of the ITP process recommended by Westinghouse, in which a smaller processing plant would handle the waste in smaller batches, to reduce processing time and avoid the buildup of benzene emissions. Westinghouse estimates it would cost $1 billion and take seven years to develop.
Despite the problems, DoE said it has not altered its 2028 target date for removal of HLW now in storage tanks at Savannah River.