More than 500 workers in the center of the Hanford nuclear reservation were ordered to take cover indoors Friday morning after steam was spotted rising from a radioactive waste storage tunnel.
The order was issued at 6:03 a.m. and lifted more than four hours later after Hanford officials confirmed that there was no release of radioactive material into the air.
On a typical work day about 3,300 workers would have been in the 300 East Area. But Friday was a day off for many employees who work 10-hour days from Monday through Thursday.
Some workers scheduled to work Friday had not arrived on site yet when the take cover order was declared.
Shortly before 6 a.m. a worker saw steam coming from a building at the end of the second PUREX processing plant storage tunnel.
The tunnel is being filled with thin layers of concrete-like grout after the 1,700-foot-long tunnel was declared at risk of a collapse.
It holds 28 rail cars loaded with obsolete and failed equipment that is heavily contaminated with radioactive waste.
The last layer of concrete added was curing early Friday morning and work had yet to begin to pump the next layer of grout into the tunnel when the steam was noticed.
The take cover order was issued as a precaution for workers in the 200 East Area in the center of the site, said Mark Heeter, Department of Energy spokesman.
An emergency was not declared and the Emergency Operations Center in the Richland Federal Building was not activated.
A crew, wearing protective gear and outfitted with filtered-air respirators was sent into the work area around the tunnel later in the morning to investigate and check for radioactive contamination.
No evidence of any radioactive release was found, said officials.
They also started generators to power lights and cameras inside the tunnel and air sampling equipment.
The cameras showed steam inside the tunnel as grout cured. The curing process generates heat and moisture, and steam inside the tunnel was expected.
But it was not expected to escape into the atmosphere through an undetected opening in the building at the end of the tunnel. It was visible as the warm air from the tunnel hit the cool outdoor morning air.
The building, which had been sealed, houses the equipment for the steel door at the end of the tunnel nearest the PUREX plant, where rail cars loaded with waste were pushed into the tunnel. The 7-foot-thick steel door is 24 feet high and 22 feet wide.
Rail cars were pushed into the tunnel for storage from about 1964 to 1996.
During the take cover alert workers stayed indoors with windows and doors closed and ventilation systems shut off. They were barred from eating or drinking for much of the four hours.
An estimated 530 to 580 workers took cover in the Friday incident.
About 350 to 400 workers were at the $17 billion vitrification plant construction site in the 200 East Area.
Another 180 workers for cleanup contractors — Washington River Protection Solutions, CH2M Hill Plateau Remediation Co. and Mission Support Alliance — were in the 200 East Area.
In May 2017, the first and shorter of the two PUREX plant’s waste storage tunnels partially collapsed. It holds eight rail cars loaded with waste.
An emergency was declared and thousands of workers were ordered to take cover indoors for several hours. Residents of nearby communities had several anxious hours before Hanford officials confirmed that no radioactive particles had been released from the tunnel.
By the end of June 2017 a structural analysis had concluded the second tunnel did not meet modern structural standards.
Concerns increased in spring 2018 when video cameras lowered into the tunnel showed showed corrosion in the bolts used to anchor steel beams to the concrete arches of the tunnel and corrosion in the beams at one end of the tunnel.
Corrosion increases the risk the tunnel could fail.
Grouting of the tunnel began as soon as the Washington state Department of Ecology, a regulator on the project, completed a public comment period and approved the work.
Since the first of the month when grouting began, workers have placed about 9,000 cubic yards of grout in the tunnel in thin layers. It is estimated to be almost 25 percent of the grout that will be needed to fill the tunnel to prevent a possible collapse.
Grouting work is expected to pause for a couple days while workers evaluate the opening in the building where steam escaped. The building was original to the tunnel, with construction of the tunnel completed in 1964.
The first tunnel was filled with grout under emergency conditions, with no delay for public comment.
It was built in 1956 using timbers and had a flat roof covered with about eight-feet of soil.
An unusually wet and snowy winter before spring 2017 may have added to the weight of the soil on top of the tunnel, contributing to the collapse of a section of the roof about 20 feet by 20 feet.
The soil on top of the tunnel fell in on the waste in the tunnel, helping prevent a release of airborne contamination.
Hanford officials are concerned that if one steel beam in the second tunnel collapses, it could put stress on the next beam, creating a domino failure effect.
The second tunnel also is covered with about eight feet of soil.
The grouting is considered a temporary measure to stabilize the tunnels and contain their waste, with a final cleanup decision not yet made for the tunnels.
Much of the waste stored in the two tunnels came from the PUREX plant.
The PUREX plant was used from 1956 until 1972 and again from 1983 to 1988 to chemically separate plutonium from uranium fuel irradiated at Hanford reactors.
The plant processed about 75 percent of the plutonium produced at Hanford for the nation’s nuclear weapons program.