The United States has about three times more waste plutonium than the last official government estimate released 14 years ago, said Robert Alvarez, senior scholar at the Institute for Policy Studies.
Hanford has been responsible for about a third of the waste, and much of it remains there, according to Alvarez's calculations.
The last official estimate of plutonium waste nationwide was 3.7 tons. But Alvarez said a better preliminary estimate is about nearly 14 tons, with about 4.4 tons at Hanford, which produced plutonium for the nation's nuclear weapons program.
"I was very surprised at the inventory of plutonium waste at Hanford," he said.
He plans to publish his findings, which are based on a review of government reports and data, in Science and Global Security, a peer-reviewed journal published by Princeton University. Alvarez was a senior policy adviser at the Department of Energy during the Clinton administration.
Plutonium waste at Hanford includes plutonium mixed in the 53 million gallons of waste held in underground tanks. The worst of that waste will be treated at the $12.3 billion vitrification plant now under construction.
It also includes suspected plutonium-contaminated waste that temporarily was buried in central Hanford starting in 1970 until DOE had a national repository for the waste. Congress ordered that such waste, called transuranic waste, be disposed of a national repository starting that year.
Enough waste to fill 72,000 55-gallon drums temporarily was buried and about two-thirds of it has been dug up. Waste that proves contaminated with plutonium at high enough levels to be classified as transuranic is being shipped to the Waste Isolation Pilot Plant in New Mexico, the nation's repository for transuranic waste.
Alvarez estimates the stored or buried transuranic waste that has been or will be sent to New Mexico accounts for about half of Hanford's plutonium waste.
But Hanford also has plutonium-contaminated waste buried before 1970 and plutonium-contaminated liquids that were discharged into the soils in central Hanford.
"A lot of this is going to be hard to retrieve," Alvarez said.
DOE has concentrated its efforts in recent years on cleaning up Hanford contamination along the Columbia River, and work is in early stages now to come up with a cleanup plan for central Hanford, where much of the plutonium waste is.
That includes characterization of waste in old burial trenches and in the soil by methods such as drilling, sampling and ground-penetrating radar. The data will be used to develop a proposal that will be reviewed by Hanford regulators, the tribes and the public before a decision is made on how to clean up the waste, according to DOE.
Any decision will be based on actual data, not estimates, said DOE spokesman Geoff Tyree.
"DOE headquarters is checking the report to see if it offers new information," DOE said in a written statement. "This doesn't appear to alter our approach to cleanup."
The DOE Office of Environmental Management has asked an independent technical review board made up of scientists from the national laboratories and DOE offices of Science and the National Nuclear Security Administration to do a more comprehensive examination of Alvarez's estimates. That's normal protocol for outside reports, Tyree said.
DOE already is concerned about discharges of radioactive waste to the soil in central Hanford. It's not practical to excavate more than 60 feet below the ground's surface but in central Hanford some contamination is as much as 300 feet deep.
DOE has proposed launching a field research center at Hanford in early 2011 to tackle the problem.
Liquid discharges from the Plutonium Finishing Plant until 1973, when discharges began to be routed to Hanford's underground waste tanks, are of particular concern to Alvarez. He believes plutonium has penetrated deep underground at high rates.
Because of solvents and salts in the liquid, plutonium may have traveled deeper than anticipated, instead of adhering to the soil closer to the ground level, he said.
Alvarez believes levels of plutonium will become the reference contaminant for central Hanford, determining cleanup standards there.
Officials with the state of Washington, a regulator on Hanford work, were on furlough Monday and not available to comment.
Estimates of plutonium waste increased since 1996 for three reasons, Alvarez said in his study. In some cases residual plutonium left at sites such as Hanford was reclassified as waste because the nation no longer needed to gather and process the residual plutonium for the weapons program.
With Hanford tank waste, better characterization by DOE showed the tanks contained about twice the plutonium estimated in 1996.
In addition, DOE did not have measurement technologies when plutonium production began that are as accurate as those used today.
Many of Alvarez's estimates were based on data DOE collected as part of a comprehensive draft study on tank waste, the Draft Tank Closure and Waste Management Environmental Impact Statement released in late October, Tyree said.