Japan's nuclear crisis was a preventable disaster resulting from "collusion,” an expert panel said Thursday. The panel urged strict checks on all reactors and said Japan's 21 oldest reactors may be at similar risk from a big quake. "This means that all of Japan's reactors are vulnerable and require retro-fitting, calling into question the hasty decision of the Noda cabinet to restart reactors," said Jeff Kingston, a faculty member at Temple University, Japan Campus.