Not that I doubted it, but US intelligence sources have confirmed that the North Koreans used plutonium in the device they detonated (or had fizzle – that's still an open question). I don't agree with the intelligence assessment that the New York Times is reporting, however.
The intelligence agencies’ finding that the weapon was based on plutonium strongly suggested that the country’s second path to a nuclear bomb — one using uranium — was not yet ready. The uranium program is based on enrichment equipment and know-how purchased from Pakistan’s former nuclear chief.
Nuclear experts said that the use of plutonium to make the bomb was important because it suggested that North Korea probably had only one nuclear program mature enough to produce weapons.
“This is good news because we have a reasonably good idea of how much plutonium they have made,” said Siegfried S. Hecker, the former chief of the Los Alamos National Laboratory and now a visiting professor at Stanford University. Mr. Hecker, who has visited North Korea and is one of the few foreigners to have seen parts of its nuclear infrastructure, said that it was his guess that “they tried to test a reasonably sophisticated device, and they had trouble imploding it properly.”
The supply of plutonium materials is known from the days when international inspectors kept tabs on the fuel rods in the North’s reactor, and intelligence analysts estimate that North Korea has enough material to make 6 to 10 plutonium bombs.
All this really suggests is that the North Koreans used plutonium. It does not actually have any bearing at all on whether they have weapons grade uranium. I would agree with Hecker that there is a reasonable chance the device was a fizzle due to improper implosion. Plutonium bombs are much harder to construct and detonate than uranium bombs. But none of this is conclusive, either.