VIENNA, Austria (AP) — The head of the U.N. nuclear agency says North Korea has asked his agency to remove its seals from the Yongbyon nuclear reactor. The move is raising concerns that the North may be preparing to restart its mothballed nuclear program. But Mohamed ElBaradei says authorities in Pyongyang say they only want to carry out unspecified tests that will not involve nuclear materials. North Korea said last week it is making “thorough preparations” to restart its Yongbyon nuclear reactor, which it began disabling last year.