Updated

Nuclear watchdogs are fighting a proposal to ship tons of plutonium to New Mexico, including the cores of nuclear warheads that would be dismantled at an aging and structurally questionable lab atop an earthquake fault zone.

Opponents voiced their opposition at a series of public hearings that opened this week on the best way to dispose of the radioactive material as the federal government works to reduce the nation's nuclear arsenal.

The Department of Energy is studying alternatives for disposing of plutonium in light of federal budget cuts that have derailed plans for new multi-billion-dollar facilities at the Savannah River Site in South Carolina.

The preferred plan under consideration calls for the shipment of 7.1 metric tons of so-called pits — or cores — of an undisclosed number of nuclear warheads now stored at the Pantex plant in West Texas to Los Alamos National Laboratory in New Mexico and the Savannah River Site for disarmament and processing into fuel for commercial nuclear reactors.

The plan also calls for another 6 tons of surplus plutonium to be buried at the Waste Isolation Pilot Plant in Carlsbad, N.M. That proposal has raised concerns about whether that waste would take up space needed for disposing of thousands of barrels of low-level radioactive waste that have been sitting for years above ground at a Los Alamos dump.

Potential threats from that waste drew attention when a massive wildfire lapped at lab property in 2011.

During the initial hearing Tuesday in Los Alamos, activists questioned the safety of bringing more plutonium to the 1970s-era Los Alamos lab known as PF-4. A federal oversight board has said the facility remains structurally unable to withstand a major earthquake. The lab was built over fault lines that were later found to have the potential for more severe earthquakes than previously thought.

Additionally, the Defense Nuclear Safety Facilities Board recently said officials had significantly underestimated how much radiation would be released if there were a major earthquake and fire at Los Alamos.

Activist Greg Mello, executive director of the Los Alamos Study Group, said he couldn't understand why using the lab was a preferred option "when these very basic problems have not been resolved."

"We are talking about a very large new mission, a type of mission for which this building was not designed," he said during the hearing.

Mello said the government should simply look at ways to safely bury the plutonium.

David Clark, a chemist and plutonium expert at the lab, countered that the facility is ideally suited for the project.

"They are disassembling pits today," he said. "They are doing it right now. It is already part of the mission. ... They have the knowledge."

Clark said he worked at the lab for 10 years and has no concerns about safety. And like other top lab officials have said, the PF-4 building is where he would want to be in an earthquake, Clark said.

He said he was not allowed to say how many pits would be involved in the plan, or how much plutonium is currently handled at the lab. He believes that taking the surplus plutonium to PF-4 would have little impact on lab operations.

"This is not going to make a dent," he said.

Clark said the mission is to ensure the plutonium can never again be used in a nuclear weapon, so creating the so-called MOX fuel is the best option.

"MOX is a proven fuel that is used around the world, in a variety of reactors," he said. "Storing plutonium glass or ceramic in canisters or underground will not reduce the global inventories. As a chemist, such waste forms may slow me down, but I can still recover the plutonium. The only one of these options that will destroy plutonium ... or make it unsuitable for weapons ... is to burn it in a nuclear reactor. "

Another hearing is schedule Thursday in Santa Fe, and a third Tuesday in Carlsbad.

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