Chris Schneidmiller
WC Monitor
8/28/2015
The Savannah River Site (SRS) this month ended an extended “safety pause” in operations of a chemical processing system that produces feedstock for the planned Mixed Oxide Fuel Fabrication Facility.
The suspension of operations began early this year following a Jan. 7 power outage at the facility. While that incident only halted work for one day, personnel at the Department of Energy site on Feb. 3 determined that agitators in one nuclear waste holding tank had not been functioning since the electrical interruption. The HB Line hold tank agitators were required only for short periods of time for sampling and transfers.
The situation with the agitators, the Aiken Standard reported earlier this year, could lead to erroneous plutonium-concentration results.
“On 2/3/15, a sample was taken from a HB Line hold tank that was within specifications but different from the expected value,” Barbara Smoak, spokeswoman for SRS managing contractor Savannah River Nuclear Solutions, stated by email. “It was determined that the cause of the unexpected sample value was that the agitators in the tank were not operating and had not been operating since the loss of power in January. SRNS identified the issue and the cause of loss of agitation.”
HB Line work was halted while Savannah River Nuclear Solutions developed a recovery plan and submitted it to the Energy Department for approval. Details of the plan were not immediately available, but the safety pause was ended and the HB Line “back to full operations” as of Aug. 6, Smoak stated.
The Defense Nuclear Facilities Safety Board in February cited the event as a failure of the site’s nuclear criticality controls. “The HB-Line Nuclear Criticality Safety Evaluation (NCSE) requires 1) agitation to assure that the tank sample is a representative sample and 2) that the NT-51 plutonium (Pu) concentration be less than 6 g/l. Thus the lack of agitation meant that all the defenses were violated and no other documented controls remained to protect the criticality safety limit,” according to a Feb. 20 DNFSB site representative report. “While the NCSE included a common mode failure (CMF) evaluation for this control set, it did not identify lack of agitation as a CMF. In addition, SRNS did not implement the H-Canyon criticality safety control that requires the NT-51 agitators to be running during transfers from HB-Line into the H-Canyon receipt tank to ensure solids remain suspended and the fissile material location is accurately tracked.”
The DNFSB site representatives also noted that HB Line personnel at the time had no direct capacity to determine that the agitators were functioning, but instead had to watch “for minor fluctuations in the tank liquid level using the charts displayed on the Distributive Control System (DCS).” Smoak said, though, that Savannah River Nuclear Solutions has since taken steps “to enable operators to positively verify tank agitation.”
HB Line has three processing lines, and is the sole chemical processing site of its kind operated by DOE. Phase II of the plant produces plutonium oxide, which is feed material for the mixed oxide plant still being built at Savannah River. The plant is intended as a means of disposing of 34 metric tons of surplus U.S. weapon-usable plutonium, but is behind schedule and over budget. A recent report from a Red Team of nuclear experts suggested downblending might be a preferable option based on cost for disposing of the plutonium.
