The Department of Energy’s Office of Environmental Management this week announced that after seven years, mining of the Waste Isolation Pilot Plant’s Panel 8 is finished. Created from an ancient salt formation 2,150 feet below the surface, Panel 8’s seven emplacement rooms are the next destination for transuranic waste brought to WIPP from DOE sites throughout the country.
In excavating Panel 8, mining machines cut more than 157,000 tons of salt rock, equivalent in weight to 1.5 Nimitz-class aircraft carriers, according to the DOE.
TRU capacity: By law, WIPP is allowed to hold 6.2 million cubic feet of transuranic waste, and the current repository design consists of 10 panels. Panels 1—8 consist of seven disposal rooms, each with an intake and an exhaust drift. Each room is 300 feet long, 33 feet wide, and 15 to 16 feet tall.
Panel 9, which is no longer accessible, and Panel 10 are made up of a portion of the main access drifts in the underground and have not been authorized for waste emplacement. The drifts are passages used for moving people, machines, waste, and air through the mine.
The DOE is currently seeking a permit modification to excavate two additional panels, Panels 11 and 12, to make up for the capacity lost from the 2014 radiological release at WIPP. As a result of that accident, which shut down repository operations for three years, the DOE was forced to close off portions of the mine due to contamination and deteriorating ground conditions.
Just-in-time mining: WIPP’s salt formation naturally creeps, closing any opening within a relatively short period of time. It is this property that makes WIPP a desirable repository site, as the salt eventually will encapsulate the waste, isolating it from the environment.
Because of salt’s propensity to creep, WIPP employs a “just-in-time” philosophy to panel mining. Mining of a panel is planned to ensure that the panel will be ready and certified just before it is needed for waste emplacement. Waste is currently being emplaced in Panel 7, and when it is full, scheduled for April 2022, Panel 8 will be ready to accept waste.
According to the DOE, power, mine phones, protective chain link on the walls, and air monitors are yet to be installed in Panel 8. But the heavy lifting—the creation of its rooms—was completed recently when a continuous mining machine removed the last of the floor in Room 3, the DOE said.
The mining: To create the rooms in WIPP’s panels, continuous miner machines make one pass through, guided by laser measuring devices, then gain the room’s final height by digging out the floor. The miners can cut 8 to 10 tons per minute, dumping the salt into haul trucks that transport the salt to a large hopper known as a grizzly. From there, the salt hoist lifts 5 tons at a time to the surface, putting it into a 40-ton haul truck for placement on the north portion of the property.
Next up for the mining machines are drifts that will run westward from the existing mine, connecting with a utility shaft under construction. A side drift will connect the new drift to the current air intake shaft, which is being converted to exhaust salt-laden mining air through new ductwork, fans, and a 75-foot-tall exhaust stack.