Nuclear mattersFirst weapons-grade plutonium found in a dump
The oldest batch of weapons-grade plutonium was found inside a glass jar buried at a dump at the Hanford nuclear reservation in Washington State
The very first batch of weapons-grade plutonium was found, encased in a glass jar inside a beaten up old safe, at a waste pit in Washington State. It was found at Hanford, the site of a nuclear reservation created in 1943 to support the U.S. pioneering nuclear weapons program. Hanford made the plutonium-239 for Trinity, the first nuclear weapon test which took place on 16 July 1945 in New Mexico. Three weeks later, more Hanford plutonium was used in the nuclear bomb that was dropped on Nagasaki.
New Scientist’s Colin Barras reports that sloppy work by the contractors running the site saw all kinds of chemical and radioactive waste indiscriminately buried in pits underground during the forty years that Hanford was operational, leading experts to describe it as the dirtiest place on Earth.
A clean-up crew found the old safe in 2004. Inside it was a glass jug containing 400 milliliters of plutonium. Recent tests by Jon Schwantes’s team at the Pacific Northwest National Laboratory in Richland, Washington, have shown this plutonium was the first ever processed at the site, and the first made on a usable scale anywhere in the world. Barras writes that Schwantes and colleagues used the fact that plutonium naturally decays to uranium to date the sample to 1946, give or take 4.5 years, by comparing the amounts of the two metals present inside the jug. Its age allowed the team to establish that the plutonium must have come from one of four reactors — out of eleven in the United States at the time — from which fuel was reprocessed into plutonium. Three of those reactors were on the Hanford site, with the fourth at Oak Ridge in Tennessee. Comparing the minor plutonium isotopes in the sample to signatures for each of the four reactors showed that the sample came from the X-10 reactor at Oak Ridge.
Now, the Hanford site’s reprocessing plant, the first in the world, was completed before the reactors nearby were ready, in late 1944. This means that the inaugural run of the reprocessor on 9 December 1944 used fuel shipped from Oak Ridge. “The very next run [and all subsequent runs] used Hanford plutonium,” says Schwantes. “We have the oldest known sample of plutonium-239 — weapons plutonium.”
His team read that a safe matching the description of the one unearthed in 2004 was sealed in 1945 because of radioactive contamination. It was disposed of in 1951, and remained lost for the next fifty years. “The contamination was not from the plutonium jug,” Schwantes says. “The jug was intact when found.”
Plutonium-239 has a half-life of 24,110 years and emits alpha particles that are too bulky to penetrate even skin or paper. It is most dangerous when inhaled as a dry powder, where its decay in the lungs can cause cancer, he adds.
Schwantes does not plan to put the sample in a museum. He is working with New Brunswick Labs to create a standard reference sample for plutonium-239 from the material, partly because of its primacy as the oldest sample. “The other factor is its extreme purity — 99.96% plutonium-239 is as pure a sample of 239 I have seen produced from any reactor,” says Schwantes.
-read more in Jon M. Schwantes et al., “Nuclear Archeology in a Bottle: Evidence of Pre-Trinity U.S. Weapons Activities from a Waste Burial Site,” Analytical Chemistry (16 January 2009), (DOI: 10.1021/ac802286a)
