Some Japanese nuclear reactors, mothballed since the 2011 Tohoku quake, may soon restart. But nature can outpace new safety precautions, warns a geophysicist.

NEARLY four years after the devastating Tohoku earthquake and tsunami that led to a severe nuclear accident at the Fukushima Daiichi power station, Japan stands on the brink of a major decision: whether to restart its nuclear power plants.

Two key questions come to the fore in such an earthquake-prone region: which hazards can nuclear plants withstand, and can society as a whole live with the risks posed by hazards that plants cannot withstand? The latter is an inherently political question.

Japan had 54 commercial reactors in operation before the disaster. Four of the six reactors at Fukushima Daiichi were damaged beyond repair in 2011. The other two are to be decommissioned.

The remaining 48 reactors were taken out of service after the earthquake. Two reactors at the Ohi plant, on the Sea of Japan coast of Honshu island, were restarted in July 2012 under the Democratic Party of Japan government, but amid legal wrangling, they have been off-line again since September 2013.

Fukushima underscored the inadequacies in the existing oversight of the nuclear industry, and the DPJ government established a new Nuclear Regulation Authority three months before it fell from power in the December 2012 elections. The NRA’s checks are ongoing, but it is expected that reactors at the Sendai plant on Kyushu island in Japan’s south-west will soon receive final approval for a restart. Why Sendai is to lead the way isn’t totally clear, but the support of the prefectural governor may be one reason.

The Sendai plant faces some specific risks. The site is about 50 kilometres from a large active volcano, Sakurajima, and there are several other active volcanoes on Kyushu. A large eruption would pose obvious safety issues for the plant, but its operator has said that advance warnings of an impending eruption would allow them to take appropriate measures. Doubts about this sanguine view were reinforced by the eruption of Mount Ontake on Honshu, without warning, in September. It killed more than 50 climbers out for a weekend stroll.

A variety of natural hazards, including earthquakes and subsequent tsunamis, pose risks to reactors throughout Japan. I have written extensively about the lack of success of both short and long-term earthquake prediction. It is well known that accurate predictions of fracture and failure phenomena such as earthquakes are, in general, impossible. Intellectually honest discussions of nuclear safety with regard to earthquakes must start by acknowledging this.

Before Tohoku, the Japanese government’s seismic hazard map assumed that earthquakes off that coast would not exceed magnitude 7.5 to 8.0. The most authoritative estimate for the size of the Tohoku quake is magnitude 9.1. Given that the energy released by an earthquake increases 30-fold for every 1.0 increase in magnitude, this is a huge discrepancy.

Despite the semi-random nature of these hazard forecasts, the fact that they were promulgated by government scientists has provided an alibi of sorts. No one has been held individually accountable for the nuclear disaster that unfolded at Fukushima Daiichi.

There was some positive news amid the disaster. The Onagawa plant, about 100 kilometres north of Fukushima Daiichi on Honshu’s Pacific coast, was hit by a roughly comparable tsunami, but a combination of a more stringent tsunami design standard, good engineering practice and a bit of good luck meant that there was no significant damage.

Both pro- and anti-nuclear advocates have argued that nuclear plants should be restarted if and only if they can withstand a “worst-case” scenario – albeit with each side trying to game the definition of the worst case. This may sound sensible, but it is logically flawed. When it comes to natural hazards there is no “worst case”. If we ratchet up the definition of worst case to magnitude 9.1, and ensure plants exceed the standards of Onagawa, will earthquake and tsunami safety be assured?

Absolutely not. Geophysicists David Jackson and Yan Kagan of the University of California, Los Angeles, estimate that we can expect one magnitude-10 earthquake in the Tohoku region over the next 10,000 years. And there is a small chance of an even bigger one.

The backdrop to the restart decision is political upheaval, as well as rising carbon emissions and electricity bills amid Japan’s increased reliance on imported gas and oil. Prior to the disaster, nuclear supplied about 30 per cent of its electricity.

Before taking power as the major part of a coalition government in 2012, prime minister Shinzo Abe’s Liberal Democratic Party pledged to restart nuclear plants if they passed regulatory checks. Now Abe has called a snap election, to be held on 14 December. A change of prime minister or government might well affect the future of nuclear energy in Japan.

But regardless of who is in power, the bottom line won’t change. There is no way to ensure absolute safety of nuclear power plants (or for that matter, anything else). The possibility of earthquakes and other natural hazards in excess of the design specifications has to be accepted from the outset. Plants must be designed to be “fail-soft”, so that earthquake damage is minimised and there is no massive release of radioactive material into the environment.

And although advice from specialists is necessary, it is Japan’s political leaders, as well as the voters who elect them, who must take ultimate responsibility for the decision to restart its nuclear plants.