By Ian Hoffman
In a top-secret ‘experiment, nuclear-weapons scientists in Los Alamos want to explode an exotic kind of plutonium inside a containment vessel of naval warship steel.
Details of the research remain classified. Yet by using such a rare form of plutonium, scientists have revived speculation that they are building and detonating full-scale mockups of the A-bombs inside modern thermonuclear weapons. The test explosions never would shatter such a multitude of atoms as to qualify as a true nuclear blast. But arms-control advocates worry the experiments still could be valuable for refining nuclear weapons and so could violate the intended spirit of a global ban on nuclear testing.
"The only reason to do this is to create an exact copy of (the first stage of a nuclear weapon)," said Greg Mello, head of the Los Alamos Study Group, a Santa Fe disarmament group. "Anybody who can do this doesn't need to worry much about the Comprehensive Test Ban."
Officials at Los Alamos National Laboratory and the U.S. Department of Energy said Wednesday that the tests are not aimed at creating new nuclear weapons, but ensuring that existing weapons will keep working as they age or their parts are replaced. "These experiments are fully consistent with the Comprehensive Test Ban Treaty. We are not planning these experiments to investigate new designs," said a DOE official familiar with the lab's plans. "These experiments are useful for understanding the physical and chemical nature of plutonium."
Dates for the tests have not been set. Scientists will perform the explosions inside a massive x-ray machine, most likely the Dual-Axis Radiographic Hydrotest facility. The first of DARHT's two x-ray beams is scheduled to start operating this summer. These machines let scientists film the first billionths of a second as a weapon's heart is crushed by high explosives. Weapons designers can use those "movies" to double-check the computer codes and simulations that are taking the place of now-forbidden nuclear tests.
This new series of plutonium tests was largely secret until the Defense Nuclear Facilities Safety Board raised questions last month about the experiments, referring to them only as a "new classified activity." Safety board analysts worried LANL scientists might rush to perform the tests without a full-blown safety review.
"Let me assure you that this is not the case," wrote Vic Reis, the DOE s assistant secretary for defense programs, in a Dec. 17 letter to the nuclear safety board s chairman, John T. Conway. The letter, obtained by Mello's organization, suggests lab scientists want to detonate greater amounts of chemical high explosives than previously used in the containment vessels. The vessels have 2-inch walls of a special steel developed by the U.S. Navy for the skins of combat ships and submarines. Safety board analysts were concerned they might not have time to be sure the vessels can lock in the exploding plutonium, a radioactive metal that can cause lung cancer when inhaled.
The DOE rates the odds of a vessel failure at less than one in a million, though some experts calculate a slightly higher risk. All agree the consequences of a plutonium release could be dire for lab workers and possibly residents downwind in White Rock and Santa Fe. A senior DOE official promised Wednesday night that Los Alamos scientists will not perform the explosive tests until the safety board is satisfied the vessels would hold and lab workers are safe from exposure to plutonium.
"We will not go forward with these experiments without DNFSB approval beforehand," the official said.
The explosions would mark a revival of LANL work from roughly a decade ago with plutonium-242, a heavier isotope than the plutonium-239 used in nuclear weapons. Plutonium-242 behaves almost identically to weapons plutonium when imploded by high explosives except it takes several times as much plutonium-242 to achieve a nuclear-fission explosion. Plutonium-242 is also less radioactive. These factors make the unusual metal an ideal stand-in for real weapons plutonium in explosive tests. "It doesn t represent a safety problem for workers or the public," said Al Stotts, a DOE spokesman in Albuquerque.
Arms-control advocates like Mello remain suspicious. He argues that weapons scientists don't need more familiarity with plutonium. "Somehow the data from these cutting edge experiments will not be used to improve the design capabilities? That's hard to believe," he said. "LANL is working to make the test ban obsolete at least for us (the United States)."