January 21, 2009

World’s Oldest Weapons-Grade Plutonium Uncovered In Dump

The world's first batch of weapons-grade plutonium ever made has been found abandoned at the world's oldest nuclear processing site.

The first nuclear reservation established in 1943 at Hanford, Washington, was built to support the U.S.'s pioneering nuclear weapons program.

The site was home to the plutonium-239 for Trinity, the first ever nuclear weapon test in 1945. More Hanford plutonium was used in the nuclear strike on Nagasaki a little more than three weeks later.

However, Hanford earned the title "Ëœthe dirtiest place on Earth' due to sloppy work by the contractors running the plant. Numerous chemicals and radioactive waste was indiscriminately buried in pits underground throughout the sites 40 years of operation.

Five years ago, clean up crews discovered 400 milliliters of plutonium in a glass jug contained inside a battered, rusted, and broken old safe.

This particular batch of plutonium was the first ever processed at the site and the first made on a usable scale anywhere in the world, according to recent tests by Jon Schwantes' team at the Pacific Northwest National Laboratory in Richland, Washington.

The researchers used the fact that plutonium naturally decays to uranium to date the sample to some time around 1946.

The sample's age allowed the team to establish that the plutonium must have come from one of four reactors - out of 11 in the US 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.

The team concluded that the sample came from the X-10 reactor at Oak Ridge after comparing the minor plutonium isotopes in the sample to signatures for each of the four reactors.

By combing through the files at Hanford, the researchers discovered the truly historical significance of their find.

The Hanford site's reprocessing plant was the first in the world and was completed before the reactors nearby were ready, in late 1944. So the inaugural run of the reprocessor on December 9, 1944 used fuel shipped from Oak Ridge.

Schwantes said the very next run and all subsequent runs used Hanford plutonium. "We have the oldest known sample of plutonium-239 - weapons plutonium," he said.

Documentation showed that the 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 50 years.

"The contamination was not from the plutonium jug. The jug was intact when found," said Schwantes.

Schwantes told New Scientist that 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.

"From the historical records, it looks as if they've got it right," said John Simpson, an expert on nuclear history at Southampton University in the UK.

"But the puzzling thing is, why didn't this plutonium make it into the bomb?"

He said the Americans were working flat out to develop nuclear capability in 1944. "It's strange that any first large batch of plutonium-239 should be stored and not used," he added.

It might have been because of the radioactive contamination to the safe it was being stored in, Schwantes believes. "The first batch would eventually have been folded back into the stockpile if not for that contamination."

Schwantes said, despite its historic significance, he doesn't plan to put the sample in a museum. He is currently partnering 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," Schwantes said.


Image Caption: Nuclear reactors line the riverbank at the Hanford Site along the Columbia River in January 1960. The N Reactor is in the foreground, with the twin KE and KW Reactors in the immediate background. The historic B Reactor, the world's first plutonium production reactor, is visible in the distance.


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