UPDATE 12:45 p.m.
A take cover order that lasted about four hours has been lifted for workers at the 200 East Area in central Hanford.
A team surveyed the area where steam had unexpectedly been spotted coming from a building at one end of a tunnel storing radioactive waste.
No evidence was found that any radioactive particles had escaped the tunnel.
Workers were ordered, as a precaution, to take cover indoors with windows and doors closed and ventilation systems shut down.
They will be returning to their planned work tasks this afternoon, according to the Department of Energy.
UPDATE 10:00 a.m.
A crew has entered the work area where unexpected steam was spotted coming from a small building at one end of the PUREX radioactive waste storage tunnel.
The crews has begun radiological surveys. No airborne release of radiological material has been reported at this time.
UPDATE 9:30 a.m.
A team was being assembled to go into the work area of the PUREX storage tunnel to investigate after steam was noticed coming from the tunnel.
The steam was spotted coming from a small building at the end of the 1,700-foot-long tunnel closest to the PUREX plant.
The building houses equipment to move a large door that was opened to allow railcars loaded with radioactive waste to be pushed into the tunnel from the mid 60s until 1996. The tunnel holds 28 railcars.
The door is 24 feet high, 22 feet wide and 7 feet thick.
About 3,300 workers are in the 300 East Area where the take cover order is issued on a typical Hanford work day. However, many workers work 10-hour shifts Monday through Thursday, so the number of workers in the area Friday was not immediately known.
Some employees scheduled to work in central Hanford may not have arrived at work before the take cover order was issued.
The take cover order remains in place as a precaution.
----------------
Hanford nuclear reservation workers were ordered to take cover indoors Friday morning in an area near the center of the 580-square-mile site.
An alert was issued at 7:12 a.m. and had not been lifted an hour later for workers in the 200 East Area.
Steam had been seen coming from the PUREX plant tunnel storing obsolete or unusable equipment that is highly contaminated with radioactive waste.
Work was underway to fill the tunnel with concrete-like grout to stabilize it after it was found to be at risk of collapse. The work began at the start of the month.
The Department of Energy said the tunnel needed to be filled because there was a risk of particles of radioactive material becoming airborne if the tunnel failed and exposed the waste it held to the atmosphere.
Another PUREX plant tunnel partially collapsed in May 2017. No airborne release of radioactive material was reported then.