The head of Japan's nuclear regulatory body has reminded its officials that nuclear power is never "100 percent safe."

The warning comes on Monday as Japan marks the 13th anniversary of the 2011 triple meltdown at the Fukushima Daiichi nuclear power plant.

The chairperson of the Nuclear Regulation Authority, Yamanaka Shinsuke, said, "Natural disasters, such as earthquakes and tsunami, are unavoidable in Japan." He was referring to the powerful earthquake that struck the Noto Peninsula on New Year's Day.

Yamanaka went on to say that an accident like the one at the Fukushima Daiichi nuclear plant should never be allowed to happen, regardless of the type of natural disaster.

He also told the officials to rethink the efforts they should undertake and make decisions based on science.

The government's agency was established as an independent authority to tighten nuclear regulations based on the lessons learned from the 2011 Fukushima Daiichi accident.

It conducts inspections and reviews necessary for the restart of nuclear power plants based on new regulatory standards, among other tasks.