Sting planned on radioactive wasp nests at Hanford

By Annette Cary, Herald staff writerJune 11, 2009 

Hanford workers are going after some of the nuclear reservation's most bizarre waste this month -- radioactive wasp nests.

There are so many radioactive nests spread over six acres by H Reactor in northern Hanford that six to 12 inches of top soil are being dug up to remove the nests.

And another 50 to 60 nests built by mud dauber wasps are spread over about 75 acres.

"We can hand dig those with a shovel and buckets," said Dave Martin, radiological engineer for Washington Closure Hanford.

The nests all were built in 2003, when a one-time series of conditions aligned. A circle about a mile wide surrounding H Reactor is the only place at Hanford believed to have the problem with radioactive mud dauber nests.

"Fortunately, they don't fly far," said Todd Nelson, spokesman for Washington Closure.

In 2003 work was under way on the basin attached to H Reactor which once held fuel irradiated at the reactor until it was processed to produce plutonium for the nation's nuclear weapons program.

To make sure no fine particles were blown from the basin during demolition, water was used to keep it damp. That created mud that was attractive to the mud daubers.

The black wasps, which are up to three-fourths-inch long, collect small pieces of mud to build tube-shaped nests for their eggs. The nests are sometimes seen under eaves in Tri-City buildings, either alone or with several finger-sized nests grouped together.

The wasps use their stingers to paralyze spiders, which are left in the nests as food for the larvae that hatch from their eggs.

At Hanford in 2003 straw had been spread over the ground when sage seedlings were planted to revegetate land.

The wasps nested underneath the straw in addition to building nests on H Reactor buildings.

Although most of the complex has been torn down, some of the nests remain in the crawl spaces of portable office trailers, in the cracks of old telephone poles and on the flashing and roofing of a clearwell, a mostly underground structure used to hold Columbia River water before it was needed at the reactor.

Because the radioactive contamination in the mud came from a basin that held irradiated fuel, the nests "are fairly highly contaminated," Martin said.

There's no harm to the wasps in removing the nests. The mud dauber wasps in the Mid-Columbia build new nests each year rather than reusing them.

Digging up the nests that originally were attached to the straw covering the ground is one of the final steps in cleaning up the debris and contaminated soil at burial grounds once used by H Reactor, said Cameron Hardy, spokesman for the Department of Energy.

The work is being done under an agreement reached by DOE and its regulator on the project, the Washington State Department of Ecology.

Washington Closure Hanford started the work by surveying for radiation. It found that six acres had "really congested nests," said Scott Parnell, project manager for work near H Reactor.

The contaminated nests in the remainder of the 75 acres will be identified individually by workers carrying hand-held surveying equipment.

Washington Closure will spend about six weeks cleaning up the nests and trucking the waste to a lined landfill for low-level radioactive waste in central Hanford.

Then the contractor also has some nonradioactive cleanup to do near H Reactor, including removing debris from the clearwell and digging up a burn pit used for trash from the reactor during its construction and operation, Hardy said.

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