The failure of the second tunnel storing radioactive waste from the Hanford Site’s PUREX processing plant could be more severe than estimated a year ago, according to Department of Energy cleanup contractor CH2M Hill Plateau Remediation Co.
Dan Wood, chief operating officer for the contractor, said new findings of corrosion in the second tunnel raise the possibility of its collapse from “unlikely” to “anticipated” and the potential severity from “low” to “moderate.” The ratings were based on DOE guidance for nonreactor nuclear facility documented safety analyses.
Wood gave a presentation Monday at a Washington state Department of Ecology public hearing near Hanford to consider whether the state should allow DOE to fill the second tunnel with cement-like grout. The Energy Department has asked Ecology to allow it to start grouting the tunnel in the next few weeks so the project can wrap up before the worst of the winter weather.
The state agency has declined to make a decision on allowing grouting until the end of a 45-day public comment period on Sept. 27. However, it continues to receive and consider additional information from CH2M on the condition of the second tunnel, with some data submitted as recently as last week.
After the May 9, 2017, partial collapse of the older of the two PUREX Plant waste storage tunnels, the state ordered a structural analysis of the second tunnel. The analysis found the second tunnel also was at risk of collapse, but concerns increased with a video inspection of its interior this spring.
The inspection found corrosion on bolts that attach steel beams that run the length of the interior of the tunnel to concrete support ribs on the exterior. Initially, the tunnel was built of steel ribs supporting corrugated steel plate roof panels. But after two collapses during construction, it was re-engineered to add steel I-beams and reinforced, arched concrete girders over the top. Most of the corrosion was found at the far end of the tunnel where a filtered exhaust system was once used.
The corrosion increases the likelihood of a collapse, Wood said at Monday’s meeting. If one steel beam fails, others could also fail in a “zipper effect,” which increases the potential severity of the collapse, he said. The steel beams could puncture the contaminated equipment and waste packages within the tunnel, heightening the risk of an airborne release of radioactive material, he said.