A U.S. nuclear weapons expert who recently visited North Korea says he saw evidence that country can produce plutonium. But he says he is not convinced the North Koreans have the capability of building a nuclear weapon.
Siegfried Hecker, a former director of the Los Alamos National Laboratory in New Mexico, was a member of an unofficial U.S. delegation that visited the secretive Yongbyon nuclear complex in North Korea earlier this month.
Appearing before the Senate Foreign Relations Committee Wednesday, Mr. Hecker said the group was given access to a storage facility where 8,000 spent fuel rods once were kept under international safeguards. He said the facility is now empty.
"For all intents and purposes, those fuel rods are gone," he said. "I asked them 'what did you do with them?' They told us 'we reprocessed them, and not only did we reprocess them, we made plutonium metal.'"
Mr. Hecker said the North Koreans had demonstrated they had the equipment and technical expertise to extract plutonium. But he was much less certain about their capability to build a nuclear weapon.
"What I saw was pretty good reactive physics and a lot of good chemical engineering to extract the plutonium, and maybe a little metallurgy. But the next step takes a lot of physics, a lot of computation, it takes a lot more metallurgy," he said. "It takes the understanding of high explosives. You have to do some high explosives, non-nuclear testing, and then it takes the rest of the materials and how to assemble them."
Mr. Hecker said he did not see such evidence during his trip.
He said he accepted the invitation to visit North Korea because of concern over what he said are the ambiguities surrounding the country's nuclear program.
"I told my hosts, the North Korean officials of the ministry of foreign affairs, that what I want to do is to bring some clarity to this great ambiguity. I said to them some of this ambiguity may be intentional, but ambiguities tend to lead to miscalculations and when it comes to nuclear things, miscalculations can be disastrous," he said.
Mr. Hecker said the North Koreans wanted to use the visit to show they had nuclear capability in an effort to strengthen their hand with negotiations with the United States.
Washington has accused Pyongyang of secretly continuing its nuclear weapons research despite a 1994 deal under which North Korea agreed to freeze its nuclear activities.
The United States, China, South Korea and Japan have been trying to persuade North Korea to restart negotiations, after a first round of talks ended inconclusively last August.