Crews at the Hanford Site in Washington state on Tuesday night started injecting grout to stabilize the Hanford PUREX Plant waste storage tunnel discovered last spring to be partially collapsed, but halted work as some dirt began to subside into the tunnel, the Department of Energy said Wednesday.
After the breach in the top of the underground tunnel was discovered on May 9, workers the next day began filling the hole with a mix of sand and soil. Some of the mix was later removed to allow placement of a trench box with pipelines tipped with lances that were pushed into void areas of the tunnel for the injection of grout intended to stabilize the tunnel.
Workers had injected 15 truckloads of grout when they noticed dirt starting to subside along the 4-by-5-foot trench box as the grout injection caused vibrations, according to Hanford officials. No radiological readings above those anticipated were detected and none of the workers were at risk, DOE said. More fill material was added Wednesday morning around the trench box.
“The workers are highly skilled and prepared for situations like the subsidence encountered with injecting grout to stabilize the tunnel,” said Doug Shoop, manager of DOE’s Richland Operations Office at Hanford.
The Energy Department anticipates restarting grouting soon and filling the tunnel by the end of the year, as previously planned. About 650 truckloads of grout are expected to be needed to fill the 360-foot-long tunnel holding eight railcars of equipment that are highly contaminated with radioactive waste from former plutonium recovery operations at PUREX.
Filling the PUREX Tunnel 1 with engineered grout is intended to not only stabilize the tunnel, but to provide additional radiological protection.
A second tunnel with PUREX waste also is at risk of collapse, according to a DOE structural analysis, but a plan for its stabilization has yet to be selected.