WORK UNDERWAY TO REMOVE MASSIVE VAULT
WC Monitor
2/14/2014
The Hanford 340 Vault, weighing about 1,100 tons, is expected to be rolled out of the ground in the 300 Area at the end of this week, weather permitting. It’s one of just two complex radioactive facilities that still need to be demolished or removed at the Hanford 300 Area by Washington Closure Hanford. The list of complex facilities there dropped from three to two in January when the Plutonium Recycle Test Reactor, weighing 1,082 tons with its shielding, was lifted out of the ground. Like the test reactor, the 340 Vault will be loaded onto a heavy-haul trailer and slowly driven to the Environmental Restoration Disposal Facility in central Hanford. The work had been planned for last weekend, but postponed because of the snow. “This will be another big piece of work accomplished on the river corridor and it has been done successfully so far,” said Larry Gadbois, an Environmental Protection Agency scientist. Getting the test reactor and the 340 Vault removed will clear the way to advance work on other contaminated infrastructure below ground, including a piping system that is expected to have some high radioactivity, he said.
The underground vault, just north of Richland, was once used to hold two 15,000-gallon stainless steel tanks that collected highly radioactive liquids through a system of underground piping from laboratories, fuel fabrication facilities and test reactors in the 300 Area. The tanks have been filled with grout. The 340 Building, also called the Waste Neutralization Facility, next to the vault was torn down in 2011, and in 2012 about 54,000 tons of soil were dug up, leaving the underground vault in a hole on a pedestal of soil.
Weight, Soil Pose Complications
Preparing to lift the vault has been complicated not only because of its weight and radioactive contamination, but because it sits on soil. Workers prepared for the lift by driving four steel pipes horizontally through the soil platform underneath it. As the 3-foot diameter pipes were pushed through, an auger mined the soil out of the pipe. The pipes were then filled with concrete to help sustain the weight of the vault. The vault, which is made of steel-reinforced, high-density concrete is about 40 feet long, 29 feet wide and 25 feet high. As the fourth pipe, or casing, was driven into the soil, radioactive contamination was found beneath the vault in the area of the vault’s sump. Sampling with probes showed cesium, strontium and americium contaminated soil in a four- to six-foot diameter area. That slowed work, but much of the contaminated soil was augered out by the installation of the fourth casing and then taken ERDF. A low-profile, mini-excava-tor typically used for mining was deployed to remove additional soil. Because it was under the vault, it was operated remotely.
With soil removed, steel beams were inserted underneath the reactor to attach to a lift frame and allow it to be lifted up 11 feet so the concrete pipes could be pulled out. Workers then were able to slide a huge steel pan under the reactor. It was jacked up and then grouted in place to prepare it for shipment to the ERDF, Gadbois said. As the soil was excavated to reveal the underground vault, a dirt road was built sloping into the hole to drive the transport trailer down to the vault and then under it. A concrete pad was poured under the vault to prevent the trailer from sinking into the soil once the vault was loaded onto it. The transport weight of the trailer is expected to be about 1,500 tons.
Most Work in 300 Area to be Completed in 2015
Once the vault is removed, the only complex facility left to be removed by Washington Closure in the 300 Area is the 324 Building, which sits over a spill of highly radioactive material. Initial radiation readings in the contaminated soil beneath the vault found radiation exposure rates up to 17 rad per hour. But radiation exposure rates for cesium and strontium under the 324 Building are as high as 8,900 rad per hour. Some engineering work on a system to remove that soil with the building standing is expected to be done this year. The 300 Area is expected to continue to be an active environmental cleanup site for more than a year. Among remaining work is removing the underground concrete structure where the Plutonium Recycle Test Reactor was housed until a few weeks ago, plus piping and waste sites associated with it. The former badge house, which is not a contaminated or complex facility, also must come down and conventional demolition techniques will be used. DOE plans to complete most environmental cleanup in the 300 Area by fall 2015, with the exception of the 324 Building.
