North Korea Sold Uranium Hexafluoride to Libya? The Evidence

by CKR

The New York Times and the Washington Post today have stories alleging that North Korea sold uranium hexafluoride to Libya. The evidence for this is said to come from actual measurements done by Department of Energy laboratories. However, the two stories give different, irreconcilable, evidence.

The New York Times says that the measurements were done at the Oak Ridge National Laboratory.

Nuclear intelligence experts said the new clues that implicate North Korea as Libya's supplier involve the fingerprints of uranium isotopes, or different forms of the element. Federal analysts, they said, took samples of the Libyan uranium and compared its isotope fingerprint with those of uranium samples from other countries and, by process of elimination, concluded that the uranium had come from North Korea.

Uranium has three main isotopes. The most prevalent is U-238, which accounts for a vast majority of natural uranium. U-235 is rare, but it is prized because it easily splits to produce the bursts of atomic energy that power reactors and nuclear warheads.

To trace the Libyan uranium, the government sleuths focused on an even rarer isotope, U-234. They did so because it turns out that concentrations of that isotope vary widely among uranium deposits and mines around the world.

....

A nuclear scientist who consults for federal intelligence agencies but was unaware of the North Korean finding said analysts could use such U-234 information to track the origin of a uranium sample, much as detectives match fingerprints from a crime scene to archives.

He said the analysts could examine the U-234 concentrations in the Libyan sample and compare it with samples from deposits from around the world. Since Western intelligence agencies have no known samples of North Korean uranium, he added, the analysis would proceed by the process of elimination.

Therefore, the strength of the North Korea conclusion would grow in proportion to the number of samples the scientists had from around the world. It is unknown how many samples exist from various uranium deposits or how many samples the federal analysts scrutinized for signs of similarity.

The Washington Post has a different story. Uranium hexafluoride was sent to Libya by North Korea. But

The determination that North Korea provided the uranium hexafluoride was made by a technical group within the Energy Department. It examined containers obtained from Libya -- which gave up its nuclear programs in a deal with the United States and Britain -- and picked up signatures of plutonium produced at Yongbyon, where North Korea has its nuclear facilities. The U.S. official said that because North Korea probably would have produced much of the uranium hexafluoride at the Yongbyon facility, this was deemed the link that connected the material in the containers to the North Koreans.

This explanation, like the NYT explanation, makes sense by itself. But the two are entirely different.

If the uranium hexafluoride was made from uranium recovered from reprocessing, then the U-234 signal would be scrambled by enrichment for use in reactor fuel or by nuclear processes in the reactor. So comparing U-234 with natural samples would make no sense, particularly if no North Korean samples were available. For the U-234 test to work, the uranium would have to be natural, not processed through a reactor.

The implications of the two are different, too. No enrichment apparatus is necessary to produce uranium hexafluoride from uranium ore, just a chemical processing plant. Plutonium traces in the uranium hexafluoride imply (as the Washington Post says) that North Korea has done reprocessing and may have done enrichment to produce the reactor fuel.

Another possibility for the origin of the uranium hexafluoride is that it could have come from the Soviet Union some long time ago. Soviet uranium processing usually combined ores and concentrates from many geographic sources, so the U-234 test would be less diagnostic and might well not fit any natural samples.

Comments

[CKR]

The Washington Post today says that Pakistan could have been the source of the UF6 found in Libya.

I was not clear on whether yesterday's WP article referred to a Libyan canister or its contents. A re-reading of that article, combined with today's, suggests that the WP was referring to the canister only, while the Times article referred to UF6 contents. So the two articles referred to different analyses of different objects.

If the reported canister contained the reported UF6, it is possible that the canister could have been filled with the UF6 after being contaminated with plutonium. The articles don't give information on this.

The more I think about the "fingerprinting" technique reported yesterday by the Times, the more doubts I have about it. Its reliability depends on the number of standards the scientists have available. The WP article says that samples from Pakistan are also not available, and I would guess that is also true for samples from Iran. Uranium is really rather common, and I would suspect that there are many deposits not represented in the standards collection. Not to mention that ore from multiple uranium deposits could have been mixed.

The IAEA didn't find plutonium in the same container, and they believe the container originally came from Pakistan.

From the WP:

"We can't exclude the possibility that the UF6 was made in Pakistan," said David Albright, president of the Institute for Science and International Security.

But Albright did not discount the possibility that North Korea may have been the source. "That has been a theory since last spring," he said. "What amazes me is why this is coming out again now, and the timing has to make one suspicious that the information is being used to pressure allies to take a tougher line with North Korea."