The Nuclear Regulation Authority (NRA) plans to set up a panel to study countermeasures to deal with volcanic eruptions neat nuclear power plants.
In the three years since the Fukushima disaster, Japan's utilities have strengthened their defenses at nuclear plants against earthquakes, tsunamis and typhoons but have largely neglected the risk from volcanic eruptions.
The NRA has said the chance of volcanic activity during the lifespan of Kyushu Electric Power's nuclear plant at Sendai was negligible, suggesting it will give it the green light. The plant lies in a region of active volcanic sites.
Critics, including some scientists who were consulted by the NRA, say that shows regulators are turning a blind eye to the kind of unlikely but potentially devastating chain of events that pushed the Fukushima Daiichi plant into a triple meltdown in 2011 when a tsunami crashed into the facility.
Kyushu Electric's business plan hinges on getting its two-reactor facility at Sendai restarted. The utility has posted 590 billion yen in losses over the past three years and is seeking a 100 billion yen bailout in new equity from the Development Bank of Japan.
Critics say the NRA safety review overestimates the power of science to predict future volcanic eruptions.
Japan lies on the "Ring of Fire", a horseshoe-shaped band of fault lines and volcanoes circling the edges of the Pacific Ocean. Japan itself is home to 110 active volcanoes.
Sendai, at the southern end of the island of Kyushu, is 50 km from Sakurajima, an active volcano. Five giant calderas, crater-like depressions formed by past eruptions, are also in the region, the closest one just 40 km from the Sendai plant.
Eruptions that form calderas are devastating, but extremely rare. Scientists believe the odds of a massive caldera-forming eruption happening in Japan are less than 1 in 10,000 in any given year.
Evidence of the most recent mega-eruption in southern Japan is the underwater Kikai caldera, which was formed by a violent eruption around 7,300 years ago. The eruption covered southern Kyushu with more than 60 centimeters of ash.
At times, the catastrophic scenarios that have been floated in debating the safety of Sendai before the NRA have sounded like a plot-line from a Hollywood disaster movie.
In one model presented by Kyushu Electric, an eruption similar to one 12,000 years ago would cover the Sendai facility with 15 centimeters of ash and block roads. The utility said it would be able to clear the ash and Sendai could still function.
Kyushu Electric also said it would install new monitoring equipment around nearby calderas and develop plans to remove highly radioactive fuel to a safer site if the threat of an eruption is detected.
The NRA is less concerned. "Our judgment is that it is unlikely that a destructive eruption would occur in the next 30 to 40 years," NRA Chairman Shunichi Tanaka said in June.© Japan Today/Thompson Reuters