Work could resume to empty radioactive waste from Hanford Tank C-101 in as little as a couple of weeks, said Kevin Smith, Department of Energy manager of the Hanford Office of River Protection, on Friday.
Wednesday night an emergency was declared when workers discovered indications that equipment being used to empty waste from the tank was leaking radioactive waste.
Workers went back Friday into the C Tank Farm, an area with Tank C-101 and 15 other single-shell tanks, to take another radiation reading at a sluicer shield box where the suspected leak was detected.
The radiation reading was slightly lower than a reading taken during an entry into the tank farm Thursday, but still above expected levels.
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Workers also wiped areas nearby to check for contamination, but found nothing unexpected, said John Britton, spokesman for contractor Washington River Protection Solutions.
Air samples picked up no chemical vapors from the mix of radioactive and hazardous chemical waste held in Hanford tanks, he said.
As a result, the barricade around the C Tank Farm was moved to the fenced-in area within the farm where workers routinely are required to wear protective clothing to enter. That allowed access to the control room trailer being used for Tank C-101, and a check found that no leak alarms had sounded, either before or after the area was evacuated Wednesday night.
Work will continue through the weekend to prepare for removing the insulation from the sluicer pump to look for any signs of contamination that would indicate a leak. The equipment is expected to be checked Tuesday and Wednesday, including shooting video footage and taking a sample of any contamination, Britton said.
The tank is equipped with a sluicing system that can use liquid waste to spray on solid waste in the tank to help retrieve it. The suspected leak may be from the sluicing equipment or a hose-within-a-hose transfer line, DOE said Wednesday.
The problem could be fixed fairly quickly. But if the pump needs to be replaced, resuming work to empty Tank C-101 could take longer than a couple of weeks, Smith said.
Tank C-110 in the C Tank Farm also was being emptied this week before the problem at Tank C-101.
Work did not resume to remove waste from C-110 on Friday.
DOE is required to finish emptying the 16 single-shell tanks in the C Tank Farm into newer double-shell tanks before October 2014 under a court-enforced consent decree.
Seven of the tanks still contain waste and DOE already has advised Washington state that two of the tanks are at risk of not being emptied by the deadline.
Smith said he was pleased with the response to the emergency Wednesday night, including efforts to ensure all workers were kept safe. DOE declared an "alert," the lowest level of emergency in the DOE protocol.
Lessons have been learned since the a spill of waste at Tank S-102 in July 2007, Britton said.
"Overall the response was much improved," he said.
A DOE investigation found that the 2007 spill could have been discovered more quickly if radiation monitors had been used to detect beta radiation in addition to gamma radiation.
That spill occurred in the early morning hours but workers initially thought an abnormal radiation reading was caused by a clog in the transfer line and the contaminated ground was not discovered until about 10 a.m. when workers saw wet soil. Workers in the area were not ordered to take cover until about eight hours after the spill, which spread to cover a diameter of about 15 to 18 feet.
Thirteen workers in 2007 reported symptoms they believed might have been connected to the spill, primarily due to breathing chemical fumes.
Wednesday night workers were taking beta readings and were alerted to the possibility of a leak because of an abnormally high beta radiation reading.
Workers immediately stopped using the Tank C-101 retrieval equipment and evacuated, according to DOE.
An alert was declared, with workers in central Hanford and near the K Reactors by the Columbia River ordered to take cover.
The current suspected leak appears to be much smaller than the 2007 spill, with fixative applied Thursday to about three square feet to avoid the spread of any potential contamination.
Four workers were taken to the Richland hospital as a precaution, but they have been cleared to return to work, while lab tests are pending.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews