The Department of Energy said this week it wants to bring in a “best and brightest” panel of experts to study the second tunnel used to store radioactive waste from the Hanford Site’s PUREX plant.
The federal agency told Washington state Tuesday that it would enhance surveillance and monitoring until it proposes a method for stabilizing Tunnel 2 with input from the panel and completes the operation. The state Department of Ecology, a Hanford regulator, had ordered DOE to propose a plan for stabilizing both tunnels by Aug. 1.
The DOE report submitted this week did not meet the state requirement, but remains under evaluation, the Department of Ecology said in a statement Tuesday.
Hanford’s PUREX plant Tunnel 1 was discovered partially collapsed on May 9, leading to three state enforcement orders for DOE to evaluate the structural integrity of both tunnels, propose a plan to stabilize both tunnels, and offer a plan to manage the radioactive waste in the tunnels.
Earlier, DOE and Ecology had agreed that filling Tunnel 1 with grout was an appropriate stabilization solution, meeting the requirements of the Aug. 1 deadline.
The Department of Ecology said that if DOE does not have a plan now to stabilize Tunnel 2, it “raises concerns that it may be difficult for Energy to comply with the third corrective action in our order, which requires Energy to submit a draft permit modification by Oct. 2 that details the plan for ensuring safe interim storage of the waste in both tunnels.”
The Plutonium Uranium Extraction Plant was used during the Cold War to chemically process irradiated fuel rods to collect plutonium for U.S. nuclear weapons. It closed permanently in 1988. Its first tunnel, built in 1956, holds eight railcars loaded with equipment highly contaminated with radioactive waste; the second tunnel, built in 1964, holds 28 railcars holding similar equipment.
The state did not dismiss outright the idea of an expert review. “Their proposal to convene a panel of experts to analyze options to stabilize Tunnel 2 and the waste in it has merit, especially if it results in a robust solution that all agree will be adequately protective,” the Department of Ecology said. However, it emphasized that it remains intent on having a draft permit modification in hand by Oct. 2, as its enforcement order dictates.
The expert panel would consider the tunnel design, operating history, and waste inventory to conduct an initial analysis of options, according to DOE’s report to the state. “The output of the panel will feed a detailed alternative analysis for Tunnel 2,” it said. “A response action for Tunnel 2 will be selected in consultation with the panel following the completion of the detailed alternative analysis.” No timeline was given.
The Energy Department told the state it would ramp up surveillance and maintenance of Tunnel 2 until the stabilization operation is completed. It is already conducting daily walk downs of the area and a video camera provides real-time observation of the exterior of the tunnel. DOE also plans to deploy more advanced remote imaging and sensing techniques. They could include a digital imaging system — possibly high-definition surveying laser technology — to detect minor changes in the surface of the tunnel over time. Ground motion or sound detection technology might be used to identify changes in the tunnel stability. A robotic or other unmanned system also is being considered to enter the tunnel to provide information about its structural condition, radiological conditions, and the location and condition of stored waste.
Options being considered for stabilizing Tunnel 2 were outlined at a public meeting in July. They include covering it with a layer of plastic, a tent, or a pre-engineered metal building. It could be filled with grout or expanding foam. DOE also is investigating filling the tunnel with sand or bentonite clay after the option was suggested at the meeting. Other options include a controlled collapse or proceeding with waste demolition.
The Energy Department is evaluating options on cost, the level of protection offered, and whether the proposed fix would interfere with eventual permanent cleanup of the tunnel. The Department of Energy also is considering how long the method would take to complete, leaving the tunnel at risk of collapse in the meantime. DOE completed a structural integrity evaluation of the tunnels in June, as required by the state order. Like Tunnel 1, Tunnel 2 was found at serious risk of collapse, it said.
