When Ban Ki Moon received word last week that North Korea might be planning to test a nuclear device, he had reason to be anxious. As South Korea's Foreign Minister, Ban is a key player in the six-party talks aimed at finding a diplomatic solution to the dispute over Pyongyang's nuclear program. A test would scuttle those talks and likely lead to a renewed U.S. push for sanctions against North Korea. And so in the middle of Chuseok, the Korean Thanksgiving, Ban, 62, was on the phone to his counterparts in Moscow, Beijing, Washington and Tokyo, building a response to the North Korean announcement. Speaking to TIME between calls, Ban said he was "much worried and troubled" about the possibility of a nuclear test. That's in part because of the impact it could have on the job he may be about to land: Secretary-General of the United Nations. "I hope this situation will not cause any problems to my current candidacy," he says.