The world's worst ever nuclear disaster happened on April 26th, 1986. It took place at Chernobyl, in Ukraine, near its border with Belarus, in what was then the Soviet Union. There were four reactors at the site, each giving 1,000 megawatts of electricity. The fault was both human error and poor design. Operators shut down the system that regulated its power and its emergency safety systems. They had the reactor running at 7 percent power, not realizing that the flawed design meant that low power meant more neutron emissions. This was compounded when they withdrew the graphite rods that controlled neutron emission.

The reactor went out of control and blew up with a huge fireball that lifted the steel and concrete lid, releasing huge quantities of radioactive material into the atmosphere. I watched it from a hotel in South Africa, as satellite imagery captured the fire raging out of control. The radiation triggered an alert at a Swedish nuclear plant, but they soon realized it had come in on the wind, and asked the Soviets if there had been an incident. Finally, the Soviet authorities, reluctant to publicize such cases, admitted that there had been an accident.

Some were killed in the explosion, and many more died of acute radiation poisoning. Massive evacuations took place. Livestock suffered for years afterwards, and there were increased cases of childhood cancers later on. The site was finally sealed with a concrete and steel sarcophagus, later deemed unsafe. Radiation spread across Europe, affecting France and Italy, and provoked a worldwide public outcry about poor design and lax safety standards.

Such a catastrophe would have been highly unlikely with a Western nuclear reactor, given the rigorous safety procedures and inspections required. They are all vulnerable to nature, though, as was shown by the Fukushima accident caused by the tsunami that followed an earthquake. Although the reactors shut down, the tsunami disabled the cooling generators, leading to three nuclear meltdowns and some release of radiation.

We learn from mistakes, however, and nuclear power is now safer because of these incidents. Although the other reactors at Chernobyl continued to operate, plans to construct a 5th and a 6th reactor were abandoned, and a process of decommissioning eventually led to the whole site being shut down. There is now, strangely, a tourist trip around the area, which two members of the ASI's Next Generation Group visited.

No more Chernobyl-type reactors will be built, and careful consideration is given to site safety in determining the location of new reactors. Sites at risk to natural disasters are avoided. The big breakthrough is in design technology, however. The pebble bed designs use fuel 'pebbles’ the size of tennis balls, and are designed to operate at, and cope with, high temperatures. Significantly, they are gas-cooled, not water-cooled, and the gas does not absorb neutrons. They are rated "far safer in every way" than the older type of reactor.

Production of energy by practically every method is in some degree dangerous. Hundreds have died in oil rig explosions. Hundreds die every year as hydro-electric dams collapse and flood villages. Coal miners are still being killed in underground fires and tunnel collapses. All have their environmental fallout, too. The way forward is not to abandon energy use and return to Stone Age technology; it is to make energy production as safe as we can, learning from disasters like Chernobyl what not to do. Compared with other energy sources, nuclear power is relatively safe and relatively clean, and will be part of energy production for the foreseeable future.