Photo/Illutration Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant (Asahi Shimbun file photo)

The Nuclear Regulation Authority (NRA) has decided to reopen its investigation into the 2011 disaster at the Fukushima No. 1 nuclear power plant after a five-year hiatus.

The watchdog suspended the inquiry after releasing an interim report on the issue.

As radiation levels within the buildings housing the crippled reactors have fallen, the NRA decided the time is ripe to restart the investigation.

The decision is timely, given that the ongoing process of decommissioning could make it ever more difficult to fathom what exactly took place.

Since it is still impossible to scrutinize conditions inside the reactors, the investigation is unlikely to clarify the entire picture. Still, even a limited investigation offers the prospect of important lessons and insights.

The NRA, established in the aftermath of the disaster, is responsible for identifying and analyzing the causes of the accident as well as the damage it incurred while ensuring the overall safety of the nation's nuclear power plants.

The body has focused its fact-finding efforts on issues that were not sufficiently addressed by the Diet and government investigative committees.

In its interim report, published in 2014, the NRA said important equipment and emergency power sources were damaged by towering tsunami generated by the Great East Japan Earthquake.

Unlike the investigations conducted by the Diet and government committees, which were based mainly on interviews with those involved, the NRA’s quest to uncover the facts involved on-site inspections at the disabled plant.

High radiation levels that impeded access to the accident site were the principal reason the entity suspended its investigation.

The NRA decided to take another look as eight and half years of work to remove debris and decontaminate the plant have lowered radiation levels significantly, making wider areas accessible.

The NRA plans to focus on how radioactive materials leaked from the reactor containment vessels and whether the reactor cooling systems were functioning properly.

It is believed, for instance, that a failed attempt to lower pressure within the containment vessel for the No. 2 reactor by venting steam containing radioactive materials caused huge amounts of hazardous materials to leak directly into the atmosphere.

Plant operator Tokyo Electric Power Co. installed the venting facilities on its own volition in response to the government’s 1992 call for additional safety measures to prevent severe accidents.

The NRA hopes to determine whether there were any problems with its design of the facilities or its installation work. It will try to gauge whether the utility was sufficiently aware of the importance of these measures and acted accordingly.

Assessing the utility’s attitude toward the possibility of a serious accident, deciding whether the safety measures were truly effective, and thus gleaning lessons from the event are all vital for ensuring that new safety regulations introduced after the disaster will work properly.

TEPCO must cooperate with the investigation in a sincere, committed manner.

The NRA’s final report on the investigation, to be released by the end of 2020, should prove useful for improving the safety of nuclear plants across the nation.

The investigation will be conducted in parallel with the decommissioning process.

They are important tasks that should be carried out in a way that ensures the effectiveness of both efforts.

The Nuclear Regulatory Agency, the NRA’s administrative arm, and the Agency for Natural Resources and Energy, which comes under the Ministry of Economy, Trade and Industry and is in charge of reactor recommissioning work, will set up a liaison office to ensure there is proper coordination in advance concerning these two vital missions.

Of crucial importance is the need to prevent the highly compartmentalized structure of the government from impeding smooth progress on both fronts.

--The Asahi Shimbun, Sept. 18