Hanford workers have been unable to find the source of an unusual radiation reading that caused an emergency alert to be declared last week at the nuclear reservation.
“We’re not ready to close the book on this. We’re still doing work,” said John Britton, spokesman for contractor Washington River Protection Solutions.
The night of Aug. 21 a higher than expected beta radiation reading was detected at a sluicer shield box, causing workers to suspect a leak.
Work was underway with the sluicing system to empty radioactive waste from single-shell Tank C-101 and transfer it to a double-shell tank until it can be treated for disposal.
Workers at Tank C-101 evacuated and other workers across a wide area were told to take cover until more was known early the next morning.
This week workers removed the insulation from the sluicer shield box and surveyed first the upper part of the box and then the lower part of the box, Britton said. The box holds a pump and the transfer head, where the line comes out of the tank.
Readings of 180,000 disintegrations per minute were reported when the emergency was declared.
But workers have found more typical readings of 10,000 to 20,000 disintegrations per minute after opening the box, which was expected because of past contamination.
Next workers will do a grid survey of the area around the sluicer shield box, methodically checking each square inch, Britton said.
That work will continue Friday, the start of a four-day holiday weekend for most Hanford workers.
No work to empty tanks in the C Tank Farm, a group of 16 underground tanks, has been done since last week.
Before work will resume, senior management at Washington River Protection Solutions will consider findings by workers. Then those findings will be forwarded to the Department of Energy.
Work had been going well to empty Tank C-101 of radioactive waste. Since December, 87 percent of the estimated 88,000 gallons of solid waste in the tank had been removed.
A sluicing system that sprays liquid radioactive waste on the solid waste in the tank has been used, along with a higher pressure water spray. Waste is moved toward a pump in the center of the tank and removed.
Work also has been stopped on Tank C-110, a second tank with waste being retrieved.
The two tanks are among seven that still hold waste in the C Tank Farm. They are required to be emptied by the end of September 2014 to meet a court-enforced consent decree.