The Nuclear Regulator Commission is questioning whether one of the leaky liquid high-level waste tanks the Energy Department has taken out of service at the Savannah River Site (SRS) near Aiken, S.C., is sealed tightly enough to meet the agency’s strict radiation leak limits for the next several millennia.
The concern — highlighted in a summary of a May teleconference between the commission and DOE that NRC posted online July 18 — centers around Tank 16H. One of the oldest and leakiest tanks at SRS, 16H was closed in September 2015 after being filled with grout to stabilize what waste remained inside it after being largely emptied during years of intensified cleanup operations by DOE liquid waste contractor Savannah River Remediation, which came on the job at SRS in 2009.
Spokespersons for both DOE and NRC said Wednesday the grouting essentially worked as planned, and that the tank is no longer in danger of leaking as it once did.
However, according to the teleconference summary, NRC in 2015 began questioning whether the annulus duct between the tank’s inner and outer hull would stay plugged up enough to limit radiation release over the next several thousand years to the levels projected in the millennia-long risk window DOE modeled when it finalized its SRS tank farm cleanup plans.
There could be “risk-significant void space remaining in Tank 16H following tank grouting,” NRC spokeswoman Maureen Conley said by email Wednesday. In addition, Conley stated, the commission is concerned the cement-like grout inside the tank could dry up, shrink back from the tank’s interior wall, and provide a pathway for “for infiltrating water to move through the system,” thus leading “to higher release rates than predicted in DOE’s long-term performance assessment.”
Tank 16H sits in a mostly-unlined concrete-filled hole in the ground. The annulus is the space between the tank’s inner hull and the concrete, which in places is lined with protective, impermeable material.
DOE captured the grouting of Tank 16H on video, but the footage did not prove to NRC the annulus was completely sealed, in part because the annulus itself “is not visible in its entirety,” even on video, Conley said.
Conley said the NRC has similar concerns about the other tanks DOE has grouted, but the commission for now appears largely satisfied with the agency’s explanation regarding the long-term suitability of grouting. The NRC’s final technical review report about the now-closed tank will be out “later this summer,” the NRC official wrote Thursday, and the commission expects no further communication from DOE about Tank 16H, in the meantime.
A DOE spokesman said in no uncertain terms that Tank 16H has been sealed up tight.
“DOE confirmed the successful grouting of the annulus, including the annular ventilation duct, through continuous video monitoring of all grouting operations, with a focused attention to the grout entering and filling the duct,” DOE-SRS spokesman Jim Giusti wrote in a Wednesday email. “This video monitoring along with DOE’s knowledge of the duct configuration and conditions supported these conclusions.”
Two underground SRS tank farms store some 36 million gallons of liquid waste left over from Cold War plutonium production for the Pentagon’s nuclear arsenal. DOE has so far closed eight of these tanks by filling them with grout and capping them off. Eight more tanks remain.
Tank 16H is notable, and merited special attention in DOE’s long-term analyses, because it actually leaked liquid waste into the surrounding environment at the H-Area Tank Farm. The leaks began in 1959, with new leaks discovered in the 1970s.
