Pyongyang has denounced the summit as an "unpardonable crime" and an "intolerable grave provocation."

North Korea's nuclear program raises fears in the West. But it will not be one of the summit's main agenda items, says Alexandra Toma, founder of the Fissile Materials Working Group.

"There is no way you cannot not talk about North Korea, but I think that, certainly, Korean experts and the Korean government recognize that the Nuclear Security Summit is much more than that," Toma said.

The safety of nuclear power plants also will be a prominent topic of discussion in Seoul, especially after an earthquake and tsunami led to a nuclear plant meltdown last year in Japan.

At a recent discussion in Washington, Kenneth Luongo, president of the Partnership for Global Security, said the Fukushima disaster showed how much work must be done to improve nuclear power safety.

"And what Fukushima has highlighted for everybody, besides the fact that you can have a major nuclear accident in a highly developed country, is that we do not have an adequate system for dealing with radioactive dangers that cross border," Luongo said.

Before the summit itself, President Obama will meet individually with several other leaders, including Russian President Dmitry Medvedev and Chinese President Hu Jintao.