Hanford reactor may be removed instead of cocooned

By ANNETTE CARY 846 words/14 April 2010/12:11Associated Press Newswires
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TRI-CITIES, Wash. (AP) - A decision could be made in June on whether to raze Hanford's K East Reactor, a break from the practice of leaving reactor cores to radioactively decay for decades.The Department of Energy has developed a tentative plan for pulling out the guts of the reactor, but continues to gather more information to make sure the work could be done safely and economically.The plan for Hanford's nine production reactors -- other than B Reactor which may be preserved as a museum -- has been to cocoon them. They are torn down to little more than their radioactive cores, reroofed and sealed up for 75 years to let radiation decay to more manageable levels.But the K East Reactor has significant contamination of soil adjacent and possibly beneath the reactor. It's left from past leaks from its cooling basin, which was used to store irradiated fuel that was not processed to remove plutonium after the Cold War ended.
Removal of all the soil that is contaminated with radionuclides cannot be completed while the reactor stands. Excavating too close to the reactor would make it unstable in case of an earthquake, said Tom Teynor, DOE K Basins federal project director.As Hanford workers began excavating beneath the basin they found the soil immediately below the basin to be as contaminated as the floor of the basin, Teynor said.
They've now excavated 15 feet beneath the basin, where contamination of radioactive cesium and strontium remains significant.
Under the working proposal for downing the reactor, work to remove the K East Reactor core could start in late 2013 and be completed in mid 2014.
By early and rough estimates, taking out the core, disposing of waste and tearing down the rest of the reactor could cost about $88 million. Waiting decades to do the work would push the cost to $1.5 billion, by DOE estimates.
Besides allowing soil to be cleaned up, the plan has other advantages.
DOE has the work force and the lined landfill site, the Environmental Restoration Disposal Facility, to do the work now. But 75 years from now, the landfill would have to be reopened to dispose of the core and a cleanup work force would need to be found or trained to do the work.
Under plans for cocooning Hanford made in 1993, the 8,000-ton graphite cores would be hauled from reactors along the river to central Hanford for disposal in 75 years. A crawler such as the one used to move space shuttles would be rolled into a hole dug beneath each reactor and then would haul the cores on new roads built to withstand the cores' weights.
DOE is relying on ongoing work to dismantle the core of a research reactor at Brook-haven National Laboratory in New York to help guide its proposal to dismantle the K East Reactor core.
However, the K East Reactor core has 109 levels of graphite blocks compared to the 34 levels in the Brookhaven reactor core, and the higher-power K East Reactor is expected have a more radioactive core.
Within the next few weeks DOE plans to drill into the K East Reactor core to pull samples. The samples will be transferred to glove boxes and shavings will be collected to determine what radioactive isotopes they contain, radiation levels and the amount of radiation protection needed if workers were to tear out the reactor core. Radiation levels also could affect the cost of the work.
Under the plan being considered, a window would be cut into the outer layers around the reactor core to allow access to take out the core.
The core measures 41 by 41 by 30 feet. It's surrounded by a 10-inch-thick steel thermal shield. Around that is a 5-foot-thick layer made of concrete heavily reinforced with rebar to act as a shield against radiation.
The shield could be removed with a series of small explosions to fracture the concrete or by cutting it with a diamond wire saw. A torch device, remotely controlled by workers, could be used to cut through the thermal shield.
A chisel mounted on an excavator then could be used to pound away at the graphite core like a jack hammer. A bucket on an excavator arm then could be used to scoop up the debris.
One of DOE's concerns is the radioactive cobalt 60 that could be in the thermal shield. It's a high gamma radiation emitter, but its radiation also decays relatively quickly. The reactor has been idle since 1971 and half the radiation of the cobalt 60 has decayed every 5.3 years since then.
While work toward a decision on whether to tear down the reactor continues, Hanford workers are removing hazardous materials such as asbestos and lead from the reactor. That work needs to be done whether the reactor is cocooned or razed.