South Korean scientists as well as leaders say the South needs the independence to recycle spent fuel rods. But some observers say that could lead to the South producing plutonium for warheads. South Koreans disavow any ambition other than to extract more uranium to fuel reactors. It would then bury the residue.
Secret talks are under way, meanwhile, on revising the nuclear cooperation agreement.
"Both our countries support the global growth of the peaceful use of nuclear energy," US Ambassador Kathleen Stephens told an influential Korean audience in mid-March. "We will continue our cooperation to guarantee the safety and proliferation-resistance of nuclear energy."
One US concern is how much faith to place in denials of nuclear ambitions while North Korea refuses to get rid of its weapons program. The US insisted on banning reprocessing in 1972 to frustrate the dream of South Korea's long-ruling Park Chung-hee that his country would become a nuclear power.
That agreement expires in 2014, but it's far from clear if the US and South Korea can resolve their disagreement by then. Pressure could mount in the South for a deterrent while the North produces ever more fissile material, already estimated at enough for six to a dozen warheads, and conducts more underground tests as it did last May and in 2006.