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.
"Does the US want to treat us as a criminal?" asks Kim Tae-woo, vice president of the Korea Institute for Defense Analyses. "Our concern is not to build a nuclear bomb, but how to dispose of spent fuel rods. If the US government continues to oppose us, that will hurt our sentiment."
Koreans try to allay suspicions. "We do not want to use the word 'reprocessing,' " says Choi Jung-bae, director of the nuclear policy division at the Ministry of Science and Technology. "We prefer to say, 'recycling' or 'reused.' "