Russia's nuclear envoy arrived in South Korea on Sunday for meetings on the North Korean nuclear standoff, amid intense diplomacy aimed at averting a greater crisis since the communist nation claimed it conducted an atomic test. Russian Deputy Foreign Minister Alexander Alexeyev visited North Korea last week, the first known senior foreign official to travel there since the Oct. 9 test. He was expected to meet later Sunday with Seoul's top nuclear negotiator, Chun Yung-woo.