Work to fill the collapsed storage tunnel at the Hanford site in Washington state with a grout-like substance has been completed, the Department of Energy said.
A storage tunnel that holds eight railroad cars loaded with radioactive waste from the PUREX processing plant on site, which was shut down in the 1950s, was found partially collapsed in May. It was immediately filled with soil and sand after workers on the Hanford campus spent several hours indoors in buildings with ventilation systems sealed on the possibility that radioactive contamination had become airborne. It had not and the site was declared safe for workers, while a long-term solution was sought for the collapsed tunnel.
The concrete-like grout has been used before on the Hanford campus as a way to stabilize hazardous material. In the future, the substance and the entombed equipment and railroad cars can be sawed into manageable pieces. This is considered a more difficult cleanup than moving the radioactive equipment without the grout in place.
The tunnel was held up by beams made of wood treated with creosote. It is believed these beams were weakened by the radioactivity over time. A similar 1,700-feet long tunnel nearby constructed with steel beams holds 28 railroad cars loaded with radioactive materials, according to the Bellingham Herald. While considered sturdier than the tunnel that collapsed, a recent study prompted by the first tunnel collapse indicated that the second tunnel, as well, is at risk of collapsing.
Discussions are underway on how to handle that predicament. Options under consideration include filling that tunnel with grout, moving the waste from the tunnel, collapsing the tunnel intentionally or building a sarcophagus on top of the tunnel.
The tunnel that collapsed is 360-feet long. Grout pouring began on Oct. 3 and was soon halted after the initial back fill material began to give way. The grout mixture was then changed to include more soil, giving it more structure until it hardened.
To avoid having lighter material float to the top of the grout, the grout was poured in layers and allowed to harden in stages, one layer at a time. One end of the tunnel ended up with 12 layers of grout, while the other end was completed with 18 layers.
The work, which was completed several weeks ahead of schedule, was contracted to CH2M Hill Plateau Remediation Co., which, in turn, subcontracted the grout injection work to Richland, Wa., company Intermech.
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