TOKYO—The chief executive of Mitsubishi Heavy Industries Ltd. said he expects Japan's idled nuclear reactors to restart operations this spring despite widespread safety concerns among the Japanese public, and that the domestic backlash against nuclear technology won't affect overseas demand.

Japan has idled all but five of its 54 commercial reactors, and has been conducting so-called stress tests to gauge nuclear plants' resilience to natural disasters. So far, no Japanese reactor shut down for regular maintenance has been...