THIS is as close as Japan has come to the dreaded genpatsu shinsai scenario – a nuclear emergency breaking out in the chaos following a huge earthquake and destructive tsunamis.

Once the crisis has passed, the questions will arise again and with redoubled force: is Japan’s nuclear power industry as secure as it constantly claims, and can any level of precaution make nuclear plants reliably safe in the world’s most seismically dangerous nation?

There are 17 nuclear power stations around the country, most on the main island of Honshu, supplying almost 35 per cent of the nation’s baseload power. Otherwise, Japan is dependent on shipments of oil and liquefied natural gas for electricity generation.

That’s why Tokyo governments and planners remain so attached to nuclear power, despite the accidents and safety failures that afflict Japan’s nuclear industry.

In 2002, Tokyo Electric Power Co was caught in a widespread structural safety falsification scandal; in 2004, five workers were killed in an accident at the Mihama No 3 plant; and TEPCO was again caught out in July 2007 when the magnitude-6.8 Niigata quake triggered a serious fire at the Kashiwazaki-Kariwa plant.

TEPCO, the world’s third-largest power utility, operates the Fukushima No 1 and No 2 nuclear plants; given its safety record, the safety quality of its operations will again be under question.

It emerged at the weekend that all three Fukushima No 1 reactors operating at the time of Friday’s magnitude-9.0 quake suffered cooling system failures. That was reportedly the result of a station blackout – the failure of emergency electric systems accompanying the loss of regular power.

That alone would seem to guarantee another searing safety interrogation for the company.

Chief Cabinet Secretary Yukio Edano yesterday warned of the risk of a second explosion at the plant, but said that reactor No 3 could withstand it as reactor No 1 did a day earlier. “There is the possibility of an explosion in the No 3 reactor, as in the case of the first reactor,” Mr Edano said.

The reactor would survive, he added, and there would be no adverse affect on the health of nearby residents. He said the risk of a second explosion had been heightened by a hydrogen build-up in reactor No 3 when cooling water levels fell.

The plant’s operator has been pumping seawater into the reactor to reduce the heat caused by the cooling system failure.

Mr Edano said that in an explosion, parts of the reactor may become deformed, but he was confident it would survive the impact, as reactor No 1 did in Saturday’s blast, and that there would not be a nuclear meltdown: “The situation would not affect human health, but we are making this announcement because we cannot rule out the possibility of an explosion.”

Obviously there is an economic limit to the amount of disaster prevention that could be installed against what was a once-in-a-century earthquake and tsunami.

But what might turn out to be a significant factor is the age of the plant – all six Fukushima No 1 reactors were commissioned in the 1970s. About 40 per cent of Japan’s nuclear-generating capacity is older than 30 years.

One of the most stringent domestic critics of the industry, seismologist Katsuhiko Ishibashi, has repeatedly pointed out that many of the country’s plants and reactors were built during a time when safety standards were generally lower and Japan was experiencing a relative lull in seismic activity.

The second and more menacing aspect of nuclear power’s vulnerability to quakes in Japan is geographic unpredictability.

Residents close to the proposed Kashiwazaki-Kariwa plant argued for decades that it was too close to an active faultline. TEPCO claimed the fault was not “live”, and courts twice upheld it, but the residents were right.

The Fukushima stretch is 300km south of the most tsunami-prone Honshu coast, and in Japan that is some margin of safety.

But even after Friday, the most severe risk of an earthquake catastrophe remains – and it is very much known.

Only 190km southwest of Tokyo and sitting astride an active fault that could well be the epicentre of the next “great earthquake”, Chubu Electric Power Co operates the Hamaoka plant.

CEPCo has taken its two oldest and most difficult reactors out of commission but it cannot change geography.

Hamaoka is located on the Shizuoka coast, a zone so historically prone to big quakes and so overdue for another that the feared event already has a name – the Tokai great earthquake.

About 15 million people live in the Tokai region but a magnitude eight quake could cause serious damage beyond 200km, putting at risk many of Greater Tokyo’s 30 million people.

A big tsunami would also be likely.

Especially after Friday, it doesn’t bear thinking about.

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