Kenneth Fletcher
WC Monitor
11/7/2014
With storage space running out for vitrified high-level waste canisters at the Savannah River Site, “double stacking” the canisters in the current storage building could be an interim solution, according to a proposal by the site’s liquid waste contractor, Savannah River Remediation. Currently the canisters are housed in a storage building under the floor in individual vaults. But with some minor modifications each vault could fit two canisters, one stacked on top of the other. Currently production of the canisters will exceed storage capacity in Fiscal Year 2019 at planned rates, but double stacking could provide adequate storage through FY’26, according to an SRR presentation. “At this point we are very interested in it, but we’ve asked for some additional information before we make a determination on whether we are going to proceed with it or not,” Jim Giusti, a spokesman for the Department of Energy’s Savannah River Operations Office said this week.
Liquid high-level waste at the site’s tank farms is vitrified at the Defense Waste Processing Facility, with the resulting canisters stored in the glass waste storage building pending eventual transfer to a repository. Funding limitations at Savannah River have delayed the design and construction of another waste storage building, though, and to avoid filling up the available space early, the site’s latest liquid waste system plan limits DWPF annual production to between 120 to 160 canisters in the coming years, down from previous rates nearly 300 per year. At the same time, SRR is also examining the possibility of aboveground storage of the canisters in shielded containers as a lower-cost alternative. This comes as DOE is in dispute resolution with South Carolina after the site has pushed back schedules for closure of tanks beyond regulatory milestones.
Double Stacking Would Take Two Years to Implement
Dependent on funding, it would take about two years before double stacking could be implemented, Brenda Green, SRR Project Manager for Interim Canister Storage Double Stack, told WC Monitor this week. The existing vaults cannot accommodate the length of two canisters as is because the canisters are elevated three feet off the ground by a support crossbar and topped off with a four-foot concrete shield plug. The necessary modification involves removing the cross bar, putting in a support plate on the floor and then installing a shorter two-foot shield plug made instead out of metal to provide radiological protection, Green said. SRR’s planning scenario is to complete about 300 modifications of individual vaults per year, though they could eventually complete the entire building if needed.
Move Possible Because of Cooler Canisters
Originally the glass waste storage building was planned to include only one canister in each vault in order to meet the design basis at the time. However, the characteristics of the canisters have changed over time. “Over the years the predicted radionuclide content of the canisters has actually lowered because we are no longer having fuel that has just been produced. There is aged material coming into the DWPF facility,” Green said.
SRR’s feasibility study studied that issue in detail. “We made sure that we looked at models of the thermal to make sure there were no concerns with challenging any of the concrete temperatures and the glass temperatures, and there is not,” Green said. “We also looked at the radiological modeling to make sure that with two canisters there would be no concerns with the dose to the employees.”
Expected to Cost ‘Significantly Less’ Than New Building
SRR did not examine the cost of the modifications in its feasibility study, but it is expected to be “significantly less than a new building,” Giusti said. “If everything they tell us is accurate, it allows us to push the project out for the next building or pad, whichever we choose to go with,” he said, adding. “It would give us a window of opportunity with our tight budgets to really focus our resources on the highest risk items, tank closure, while we look at how we would fund the replacement facility.”
But canister storage is just one of the factors limiting high-level waste processing rates, and increasing storage capacity does not mean that tank closure delays will be mitigated, Giusti said. “We still have a funding issue. If our budget doesn’t change, then we are set at 125 canisters whether we have room for 300 or 400,” he said. “There are multiple things that are driving our canister production. While we may increase the canister storage capacity it doesn’t mean that we will be able to produce more canisters. It gives us the opportunity to increase it if all the other issues are addressed.”
