Two Hanford workers are being checked for radioactive cesium 137 in their bodies after a seal on a pipe from a waste storage tank failed.
If they did have an internal uptake of cesium 137, it was at a very, very low level, said John Britton, spokesman for Washington River Protection Solutions, the Hanford tank farm contractor.
Workers were doing maintenance in the 242-A Evaporator facility when the problem was discovered, Britton said.
The evaporator is periodically used to reduce water in Hanford's double shell tanks to make more space for radioactive waste being emptied into them from Hanford's leak-prone single-shell tanks.
Hanford has 56 million gallons of radioactive and hazardous chemical waste stored in underground tanks awaiting treatment for disposal. The waste is left from the past production of plutonium for the nation's weapons program.
Last week, workers were in the condenser room, where radioactive waste is processed when the evaporator is operating, when one worker felt air coming through a pipe and told the shift manager, Britton said.
The cause was determined to be a failed seal on a pipe from a double-shell tank of radioactive waste, which provided a pathway for vapors from the head space in the tank into the room where maintenance was being done.
Work was stopped and industrial hygienists were brought in to check for chemical vapors and radiological control workers were brought in to check for radioactive contamination. Both found nothing, Britton said.
The room was being monitored for radioactive contamination and no alarms had sounded. Workers also had not reported smelling any chemical vapors.
However, Washington River Protection Solutions tracked down 29 workers who had been in the room over about two weeks and sent them to Pacific Northwest National Laboratory for a whole body count, a check for internal contamination.
Twenty-seven of the tests came up negative, but the test detected cesium 137 in two workers slightly above the minimum detection level. However, the whole body counts have about a 5 percent rate of false positives.
The two workers are undergoing urine analyses to provide a definitive answer to whether they inhaled or ingested cesium 137. Results will be ready in about two weeks.
The checks are a conservative approach to discount the presence of radioactivity, according to Washington River Protection Solutions.