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 and reflect the potential radiation exposure for nearby workers and the public.
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.
During the Cold War, the Plutonium Uranium Extraction (PUREX) Plant recovered plutonium from irradiated fuel rods at Hanford as part of the site’s mission to provide the weapons material for the U.S. nuclear arsenal. The facility closed in 1998.
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.
“Structural failure has to be anticipated. It is going to happen,” according to Wood. “It’s a 60-year-old facility. It is corroded. Sooner or later it is going to go.”
Ecology allowed the first tunnel to be grouted without public comment under emergency conditions, with work starting last October and finishing in less than two months. The first tunnel, which was built by 1956 of timbers with a flat roof, is just 360 feet long and stores eight railcars loaded with obsolete or failed equipment that is highly contaminated with radioactive material. Grouting the tunnel required 521 truckloads of the material, or about 4,434 cubic yards.
The second tunnel, which was built about eight years later in 1964, is about 1,700 feet long and holds 28 railcars holding similar contaminated equipment from the PUREX plant and other Hanford projects. The Energy Department estimates it will take about 5,000 truckloads of grout, or about 43,000 cubic yards, to fill.
No airborne release of radioactive contamination was detected after 8 feet of soil in a berm over the first tunnel collapsed last year on top of the waste in storage. The second tunnel also is covered with 8 feet of soil, which could similarly mitigate the effects of a collapse, according to Hanford officials.
CH2M proposes to use an engineered grout mix designed to flow 300 feet before setting, to be added through six of the 17 risers that penetrate from the ground into the interior of the tunnel. Only a couple of inches would be added at a time, with the grout allowed to cure before a new layer is added. The contractor has awarded subcontracts totaling $13 million to North Carolina-based Intermech for grouting the second tunnel. Intermech, which has a location near Hanford in Richland, Wash., had a $2.8 million subcontract from CH2M for grouting the first tunnel.
In September 2017, a DOE-appointed expert panel recommended grouting the second tunnel. It determined grouting would be the best option to prevent a possible collapse and release of airborne radioactive particles until a final cleanup decision is made. The Energy Department announced in December 2017 that it had adopted the panel’s recommendation.
At the Monday hearing, Ecology heard public concerns that grouting the tunnel could easily become the permanent cleanup solution by default, with the covered waste left in place under an engineered cap to keep out precipitation. The Energy Department has said the grout could be sawed out in pieces and taken to an approved disposal site, if that is the eventual cleanup decision.
The Tri-City Development Council (TRIDEC) and Hanford Communities, a coalition of local governments, both called for grouting the tunnel as soon as possible. That is needed primarily to protect workers, the public, and the environment, TRIDEC said. But there are also concerns about protecting the reputation of local agriculture and business interests.
The partial collapse of the first tunnel in 2017 was the top-trending Twitter topic in the United States that day until President Donald Trump fired FBI Director James Comey, according to a DOE analysis.
“News of the tunnel breach quickly spread, with major U.S. and international news organizations posting inaccurate stories leading to rampant speculation and misinformation being distributed, which was detrimental to the community,” TRIDEC said in an Aug. 6 letter to Ecology. “Regional agricultural producers were getting questions about the safety of their products, and sports organizations were even reconsidering whether or not to hold tournaments in the Tri-Cities.”
That was the reaction when a breach of 20-feet-by-20-feet was discovered with no airborne radiation detected. “Imagine if a catastrophic collapse happens,” said Pam Larsen, executive director of Hanford Communities.
The Energy Department is not yet working on a plan for final disposition of the tunnels.
