Ka-boom — Saturday explosion to topple Hanford vent stack

The 200-foot-tall ventilation stack at Hanford’s Plutonium Finishing Plant is scheduled to crash to the ground Saturday after explosives are detonated.

It’s the next step toward getting the high-risk plant at the nuclear reservation torn down to the ground by the end of September.

The plant was used during the Cold War to convert plutonium that came into the plant in a liquid solution to metal buttons the size of hockey pucks or a powder, to be shipped to the nation’s nuclear weapons production facilities.

DOE officials have called it the most hazardous demolition project at the nuclear reservation.

Workers have spent several weeks preparing for the stack to come down.

Most recently, part of the base of the plant’s ventilation stack has been cut out, much like a logger would cut a wedge in a tree trunk, to control where it will fall onto a gravel pad laid for the demolition.

“This will allow it to be a fairly cushioned landing for it and allow it to break evenly when it comes down,” said Kelly Wooley, Plutonium Finishing Plant deputy project manager for CH2M Hill Plateau Remediation Co.

The concrete stack should pancake when it hits the ground, said Tom Teynor, DOE project manager for the plant.

The crumbled pieces can then be loaded into containers to be hauled to a lined landfill for low-level radioactive waste in central Hanford. The stack is about 18 feet in diameter at the bottom and about 14.5 feet at the top.

Air went through a series of filters before it was sent up the stack, but it still has low-level radioactive contamination.

Before the ventilation system fans were disconnected, they were used to blow fixative up the stack to glue any low-level radioactive contamination in place, until the blue fixative could be seen coming out the top of the stack.

The mostly underground ventilation building, housing powerful exhaust fans to serve all of the Plutonium Finishing Plant and its laboratories, has been demolished to make way for the explosive demolition of the stack.

The building, also called the fan house, was roughly 100 feet long, 40 feet wide and 20 feet deep. A radioactively contaminated vacuum line and hazardous materials such as asbestos were removed before the upper portion was demolished and the building was backfilled with clean soil.

Demolition work shifted this summer from the plant’s highly contaminated Plutonium Reclamation Facility to the fan house to be ready for subcontractor Controlled Demolition Inc. to take down the stack.

Demolition has not resumed at the facility on one end of the Plutonium Finishing Plant since an air monitor alarmed in early June, indicating a spread of low levels of radioactive contamination that has since been contained and cleaned up.

The partially demolished facility has been put into a safe and stable condition while work has temporarily shifted to the fan house, Wooley said.

Getting the nearby ventilation building and stack down will allow better access for demolition of the Plutonium Reclamation Facility and the main area of the Plutonium Finishing Plant, Wooley said.

Demolition should begin in late July on the main portion of the plant, starting with a one-story area used for locker rooms and preparations to enter the production areas of the plant.

Work also will be done to demolish the main plant at the end closest to the Plutonium Reclamation Facility. It will allow more demolition area for the facility, which is the most heavily contaminated portion of the Plutonium Finishing Plant. Because of the potential airborne contamination, just a 2-foot-wide slice of the building, top to bottom, will be taken down each day.

“Even though we have resequenced the facility demolition order, we are still working to meet the TPA (Tri-Party Agreement) milestone basically by the end of September,” Teynor said. “That has not changed.”

With no more ventilation in the plant, workers have switched to a daily shift that starts at 4 a.m. to allow them to finish work before the heat of mid-afternoon each day.

“They have done a very good job of working safely and methodically,” Teynor said.

This story was originally published July 14, 2017 at 6:50 PM with the headline "Ka-boom — Saturday explosion to topple Hanford vent stack."