TOKYO — Japan’s nuclear regulator announced an overhaul of the country’s nuclear safety guidelines Wednesday, the first since a giant tsunami swept over a nuclear power plant in northeastern Japan two years ago and set off the world’s worst nuclear accident since Chernobyl, even as signs of new trouble at the stricken plant underscored the hazardousness of the site’s cleanup.

Prime Minister Shinzo Abe has been pushing to restart some of Japan’s 50 commercial reactors, all but two of which remain idle amid public anxiety over nuclear safety in the wake of the 2011 disaster, when a powerful earthquake and tsunami ravaged the Fukushima Daiichi nuclear power plant. The announcement of the new guidelines starts a process that could allow some of the country’s idled reactors to come back online early next year.

The new guidelines were announced by the Nuclear Regulation Authority, which was set up last year to replace the previous regulator amid outrage over its lax approach to safety and close industry ties. In the future, nuclear plant operators must bolster their tsunami defenses and check for active earthquake faults under their plants. They must also set up emergency command centers and install filtered vents to help reduce the discharge of harmful radioactive substances from the reactors.

These safety standards are legally binding, unlike previous guidelines, which were not backed up by law and were adopted by nuclear operators on a voluntary basis. They also address, for the first time, the possibility of severe accidents like the Fukushima disaster, which set off multiple fuel meltdowns and forced more than 100,000 people from their homes.