The Nuclear Regulation Authority (NRA) plans to restart its investigation into the 2011 disaster at the Fukushima No. 1 nuclear power plant now that radiation levels have dropped at the site.

The NRA judged that investigators will be able to approach key equipment at the plant to obtain new information for an analysis into the causes of the accident.

The nation’s nuclear watchdog will compile a report on the results of the investigation within 2020, ahead of the 10th anniversary of the nuclear accident in March 2021.

An examination council whose members include outside experts will be reopened to conduct the investigation.

The NRA was established after the Great East Japan Earthquake and tsunami on March 11, 2011, led to a triple meltdown at the plant operated by Tokyo Electric Power Co. The NRA’s purpose was not only to strengthen safety standards at nuclear plants but also to clarify the causes of the Fukushima accident.

In 2014, the NRA compiled a report on the results of its investigation into unclarified problems at the plant. It then suspended the investigation because radiation levels at the site were too dangerous.

Under the restarted investigation, the NRA will look into the routes of radioactive substances that leaked from the plant, and whether equipment to cool the reactors were working appropriately.

The watchdog will also investigate whether TEPCO gave appropriate consideration for measures to prevent severe accidents before the tsunami swamped the plant, NRA Chairman Toyoshi Fuketa said.

Meltdowns occurred in the No. 1, No. 2 and No. 3 reactors.

At the No. 2 reactor, there is a high possibility that “venting,” the practice of releasing steam, including radioactive substances, to reduce pressure in the containment vessel, failed.

That failure is believed to have led to a large amount of radioactive substances leaking directly from the containment vessel.

The NRA will study the conditions in the containment vessel to determine where the radioactive substances leaked from.