Sunday, March 27, 2011

Nuclear power again

Also from New Scientist:

The explosions and radiation spills at the Fukushima Daiichi power station in Japan may give an unfair impression of the risks associated with modern nuclear energy generation. The Fukushima reactors are a 40-year-old design. A new generation of reactors, with more comprehensive safety features and power backups, would likely have fared much better. Alexis Marincic, chief technical officer of French reactor-maker Areva, claims that most of the failures that led to Fukushima's radiation leaks would probably not have happened with the latest designs.

Problems began at Fukushima when it lost electrical power to its reactor cooling systems after the earthquake damaged power lines to the plant and the tsunami engulfed its backup diesel generators. Areva's European Pressurised Reactor (EPR) has six backup diesel generators in two seismically damped, waterproof concrete buildings sited 50 metres either side of the containment. “Even if an aircraft crashes into the reactor building we will still have backup power for cooling,” says Marincic. The EPR also has four separate backup circuits for the electronics, pumps, valves and pipework that keep the core cool in an emergency.

Lacking cooling, some reactors at Fukushima overheated, splitting water molecules to produce hydrogen, which then ignited. This blew the roofs off the containment buildings and released steam contaminated with radioactive isotopes. To avoid this, the EPR has a catalytic hydrogen recombiner that ensures any hydrogen generated reacts with oxygen to reform water. The reactor is kept in a double-walled, leakproof containment to stop gases escaping. An inner steel-lined prestressed concrete shell 0.8 metres thick is surrounded by a 1-metre-thick reinforced concrete shell.

We still don't know if there was a core meltdown at Fukushima but the EPR guards against this too, says Marincic. The design includes a water-cooled concrete “core catcher” that stops a melting core from exploding. Two EPRs are now being built, one in Finland and one in France. Areva's rival, Westinghouse Electric, owned by Toshiba of Japan, is building a third-generation reactor of its own, the AP1000, at a site in China. Like the EPR, it has stronger doubled-up containment and multiple cooling system backups. It also has a passive safety feature: an enormous tank of water in the roof that is automatically released in the event of a cooling system loss. Effectively, this would do what the Fukushima workers did with pumped seawater, says John Gittus, former safety director at the UK Atomic Energy Authority, but without requiring pumps. “A flap opens and out it pours,” he says. “We've calculated that a tank of water that can flood the pit that the reactor sits in can cool it for 72 hours, giving operators a good three days to work out how to deal with the situation,” says Westinghouse spokesman Adrian Bull.

Both reactor designs impress Andrew Sherry, director of the Dalton Nuclear Institute at the University of Manchester, UK. “These new reactors would have managed the core residual decay heat in a Fukushima situation – and once you have managed that your reactor would be in a safe shutdown mode.” Complex safety systems won't come cheap. “But cost is not such an issue,” says Gittus. “Regulators won't let people buy reactors that might go wrong.”

We tend to trust the Japanese as efficient engineers, but their 'shame' culture leads them to cover-up their mistakes rather than admit them. Consider the failings of their nuclear industry:

December 1995 Coolant leaks from a pipe at the Monju fast-breeder reactor. Managers supply a doctored video excluding the worst of the spill.

March 1997 Fires and an explosion hit the Tokaimura waste reprocessing facility. Radiation levels are found to be at least 10 times as high as initially reported. Seven maintenance staff are later found to have been out playing golf.

September 1999 In what is billed as the worst nuclear accident since Chernobyl, three workers at Tokaimura inadvertently create a critical mass of uranium, triggering chain reactions. Two workers eventually die; six managers are arrested and charged with professional negligence.

September 2002 Newly revealed reports from the International Atomic Energy Agency, dating from the 1990s, describe safety precautions at Japanese reactors as dangerously weak, with 90 deficiencies in safety procedures. Four companies – TEPCO, Chubu Electric Power, Japan Atomic Power and Tohoku Electric Power – admit they have hidden flaws from regulators.

August 2004 A steam leak from a power turbine at the Mihama plant kills four people and injures seven. The Kansai Electric Power Company is criticised for not inspecting the failed pipe.

March 2006 A diplomatic cable from the US embassy in Tokyo, later released by WikiLeaks, discusses a case in which a court orders the Hokuriku Electric Power Company to shut down a reactor at its Shika nuclear plant because of concerns over its ability to withstand powerful earthquakes. Both the company and the Japanese government oppose the ruling.

July 2007 Three reactors at the world's largest nuclear plant, Kashiwazaki-Kariwa, shut down after a 6.8-magnitude quake. TEPCO initially says that the quake caused no radiation leaks, but days later admits that 1200 litres of radioactive water have washed into the sea.


Wayne said...

Uranium is highly dangerous easily contaminating material just to boil water with, especially when the private sector insurance industry refuses to insure these plants. The byproduct of most nuclear reactors can and will be used to build hideous weapons and the radioactive junk that will have to be dealt with after the life of the reactor is over is an example of a technology that represents unacceptable risk. Far too much of the cost and risk of mining the uranium, insuring the reactors and decommissoning the spent reactors will fall to the tax payer and not to those companies who build them.


Terry Hamblin said...

Still kills far fewer people than coal. In the UK the costs have ben shifted to the energy companies and nuclear does not even receive the 'carbon' subsidies that wind power does. I am afraid the days of rubbing two sticks together to boil a kettle are gone.

Grateful said...

Japanese-American woodworker George Nakashima told of working outside in cold weather as an apprentice in Japan. The way to keep warm was to work hard, so acknowledging that it was cold meant that you were goofing off. I suspect this same mindset impacted Japanese officials when they spoke of the early conditions at the damaged reactors. Even when their statements were translated into English, the statements were still from the Japanese mindset.

Best wishes for your recovery.

Peter Woodfellow said...

I was really worried about the incidents in Japan, What worries me is there after water stop circulating and there was a build up of hydrogen there was no means to release the hydrogen to stop an explosion without a huge contamination of the land surrounding, Who designed these systems did not have enough backup systems at all.