Unusual radiation readings that caused an emergency to be declared last month at Hanford came from old contamination, according to Hanford officials.
No evidence of a new leak from the system being used to retrieve waste from a Hanford tank or from the system's transfer hoses was found, Hanford workers were told Tuesday.
An investigation concluded that insulating blankets that had shielded radiation on an area about 4 square inches shifted, causing the elevated beta radiation readings during routine monitoring, Kevin Smith, manager of the Department of Energy Hanford Office of River Protection, said in a message to employees Tuesday.
Washington River Protection Solutions, the DOE contractor for the tanks farms, has completed an assessment of the Tank C-101 sluicer, where the elevated reading was recorded and the surrounding area and found no additional contamination or exposure to the environment, according to Smith. Employees of URS Corp. also helped with the investigation.
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The contamination was on the concrete cover block near the base of the C-101 sluicer transfer hose cover assembly, according to a memo from Dave Olson, president of Washington River Protection Solutions.
The sluicer is part of the system being used to empty radioactive and hazardous chemical waste from the single-shell tank and transfer it to a newer double-shell tank for storage until it can be treated for disposal. Underground tanks at Hanford hold 56 million gallons of waste left from the past production of plutonium for the nation's nuclear weapons program.
Because the abnormal reading could have been caused by a leak, workers at the C Tank Farm evacuated and workers in central Hanford and near the K Reactors were ordered to take cover indoors.
Work is expected to resume this week to pump waste from Tank C-101 and a second C Farm tank, C-110, where waste was being removed before the abnormal radiation readings were detected the night of Aug. 21.
Before work restarts, the hot spot will be covered.
The Washington State Department of Ecology is encouraged that the delay in retrieving waste should be fairly brief, said spokesman Dieter Bohrmann.
DOE faces a court-enforced consent decree to have all 16 tanks in the grouping called C Tank Farm emptied to regulatory standards before October 2014. Seven of the tanks still hold waste.
Washington River Protection Solutions will review actions from the incident to look for possible improvements.
However, Smith has said that employees for the contractor and DOE handled the incident well. Olson praised what he called a "professional response."
w Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews