Experts Say North Korea May Be Producing Fuel for Nuclear Reactor SEOUL, South Korea - Satellite imagery suggests that North Korea may have begun producing fuel rods for its recently restarted nuclear reactor, a United States-based research institute said in a report published Tuesday. The signs of new activity at North Korea's main nuclear complex in Yongbyon, north of Pyongyang, follow the country's repeated assertions that it is strengthening its capabilities to produce nuclear arms. North Korea, which has conducted three nuclear tests since 2006, the most recent in February, has used spent fuel rods from the reactor as a source for plutonium, a key component for nuclear weapons. The five-megawatt reactor was restarted earlier this year after a six-year hiatus. Its ability to produce plutonium again depends in part on how quickly North Korea can supply it with new fuel rods. North Korea is believed to have only 2,000 fuel rods in its inventory, a quarter of the 8,000 needed for a full load of fuel. The U.S.-Korea Institute at Johns Hopkins University reported Tuesday on its website, 38 North, that a building in Yongbyon retooled to produce fresh fuel rods for the reactor appeared to be operational. The institute said it had reached that conclusion by analyzing commercial satellite images of the complex. An old building once used to make fuel rods for the graphite-moderated reactor has been converted into a uranium-enrichment plant, which North Korea showed to visiting American nuclear experts in 2010. North Korea said it was enriching uranium to make a type of fuel needed for a separate light-water reactor it was building in Yongbyon. But highly enriched uranium can replace plutonium as fuel for nuclear weapons. Nonproliferation experts have expressed concern that the light-water reactor under construction in Yongbyon could be a cover for making bombs. North Korea itself has threatened to use all its nuclear facilities to expand its arsenal. On Tuesday, the U.S.-Korea Institute also identified another building in Yongbyon that it said could be used to produce fuel for the light-water reactor. The 25-30 megawatt light-water reactor may not become operational until late 2015 or 2016, it said. "The identification of these facilities indicates a more wide-ranging, extensive effort by North Korea to modernize and restart the Yongbyon complex" than previously understood, the institute said. Six-nation talks on ending North Korea's nuclear ambitions collapsed in 2008. The following year, North Korea expelled United Nations nuclear monitors from Yongbyon. It has since begun reactivating the facilities there, which had been taken offline under a short-lived nuclear disarmament deal. North Korea recently said that it was willing to resume the six-nation talks. But Washington and its allies, saying that they were cheated by the North during the earlier negotiations, do not plan to rejoin the talks and will continue to apply economic sanctions until North Korea demonstrates its willingness to give up its nuclear weapons. Separately on Tuesday, an Irish betting company that had been sponsoring Dennis Rodman's basketball initiative in North Korea said it had cut its ties with the former N.B.A. star. In a brief emailed statement, the company, Paddy Power, said it had made its decision "given changed circumstances," without elaborating. Mr. Rodman, who has said he considers the North Korean leader Kim Jong-un a friend, finished his latest trip to the country on Monday. Paddy Power said that Mr. Rodman would proceed with his plan to hold an exhibition game in Pyongyang on Jan. 8, Mr. Kim's birthday, between a North Korean basketball team and a team of former N.B.A. players.