Work stopped Wednesday morning at parts of the Hanford vitrification plant after radioactive contamination was detected under a birds nest, according to Bechtel National.
The contamination is suspected of coming from mud used for the nest, which may have belonged to a swallow, said Bechtel spokesman Todd Nelson. Only a small amount of contaminated soil was found, and the contamination was at a low level.
About 130 workers were surveyed for contamination, but none was found, Nelson said. They had been working in two buildings, the High Level Waste and Pretreatment facilities, that are not yet enclosed.
Union construction workers at the two buildings were sent home early Wednesday. Radiological surveys of the plant were continuing Wednesday afternoon, and any affected areas were planned to be barricaded before workers return to the construction site todayThursday.
The vitrification plant is being built to treat up to 56 million gallons of radioactive waste. None of the waste has been pumped to the plants campus as construction continues.
Routine radiological surveys are conducted, however, to monitor for waste that might be spread from the rest of Hanford. The 586-square-mile nuclear reservation is contaminated from the past production of plutonium for the nations nuclear weapons program.
Contaminated animals are an occasional problem at Hanford, although information was not available Wednesday about whether contamination had ever been known to be spread to the vit plant before now.
In 2008, Bechtel called in pest control help after pigeons roosting at the plant caused a work hazard with slippery but nonradioactive droppings. About 130 pigeons were killed with air rifles early in the summer and more were killed in September of that year.
Bechtel tried unsuccessfully to scare the birds off with noise makers and plastic owl decoys before killing them.
In 2010, Hanford drew international media attention when radioactive rabbit droppings and then the radioactive rabbit leaving the droppings were found at Hanford just north of Richland. Although rabbits occasionally get into waste at Hanford, the incidents usually occur near the center of the nuclear reservation, which is closed to the public.