How many meltdowns have there been

Nuclear Regulatory Commission in The Mainz researchers did not distinguish ages and types of reactors, or whether they are located in regions of enhanced risks, for example by earthquakes. After all, nobody had anticipated the reactor catastrophe in Japan. Subsequently, the researchers determined the geographic distribution of radioactive gases and particles around a possible accident site using a computer model that describes Earth's atmosphere.

The model calculates meteorological conditions and flows, and also accounts for chemical reactions in the atmosphere. The model can compute the global distribution of trace gases, for example, and can also simulate the spreading of radioactive gases and particles.

To approximate the radioactive contamination, the researchers calculated how the particles of radioactive caesium Cs disperse in the atmosphere, where they deposit on Earth's surface and in what quantities.

The Cs isotope is a product of the nuclear fission of uranium. It has a half-life of 30 years and was one of the key elements in the radioactive contamination following the disasters of Chernobyl and Fukushima. The computer simulations revealed that, on average, only eight percent of the Cs particles are expected to deposit within an area of 50 kilometres around the nuclear accident site.

Around 50 percent of the particles would be deposited outside a radius of 1, kilometres, and around 25 percent would spread even further than 2, kilometres. These results underscore that reactor accidents are likely to cause radioactive contamination well beyond national borders. The results of the dispersion calculations were combined with the likelihood of a nuclear meltdown and the actual density of reactors worldwide to calculate the current risk of radioactive contamination around the world.

According to the International Atomic Energy Agency IAEA , an area with more than 40 kilobecquerels of radioactivity per square meter is defined as contaminated. The team in Mainz found that in Western Europe, where the density of reactors is particularly high, the contamination by more than 40 kilobecquerels per square meter is expected to occur once in about every 50 years. It appears that citizens in the densely populated southwestern part of Germany run the worldwide highest risk of radioactive contamination, associated with the numerous nuclear power plants situated near the borders between France, Belgium and Germany, and the dominant westerly wind direction.

If a single nuclear meltdown were to occur in Western Europe, around 28 million people on average would be affected by contamination of more than 40 kilobecquerels per square meter. In terms of the number of deaths from accidents, hydroelectric power is the deadliest method of generating electricity. It has been concluded in studies conducted by, for example the World Health Organisation, that the radiation health effects of nuclear accidents have been very small.

The main impacts of nuclear accidents were not caused by radiation exposure, but instead were due to psychological and socio-economic factors resulting from misconceptions and fears about radiation — and so could have been largely avoided. Further information can be found on the information page regarding radiation and health effects. The most serious nuclear accident took place on 26 April at the Chernobyl nuclear power plant in Ukraine then part of the Soviet Union.

It is the only nuclear accident in the history of commercial nuclear power to have caused fatalities from radiation. Several factors, including reactor design issues and a poor safety culture, led to a failed safety test that caused two explosions, a fire that lasted for over a week, and the release of a large amount of radioactive material.

There were also about thyroid cancer cases of which 15 have proven fatal so far , many of which could have been avoided by preventing the consumption of contaminated foodstuffs, such as milk.

Follow-up studies have firmly concluded that the accident has not caused an increase in birth defects or hereditary effects, and no measurable increase in solid cancers beyond thyroid cancer has been detected.

Since the accident there has been a continuous clean-up of the site and the neighbouring areas. A concrete shelter was rapidly built over the damaged reactor to stop further releases of radioactive material. This was a temporary solution, and it was eventually replaced by the New Safe Confinement structure, construction of which was completed in July Thirty-five litres of a highly enriched uranium solution leaked during transfer.

Release of large quantity of radioactive material, contained within the installation. Overexposure of a worker at a power reactor exceeding the annual limit. Partially spent fuel rods undergoing cleaning in a tank of heavy water ruptured and spilled fuel pellets.

Fatal overexposures of workers following a criticality event at a nuclear facility. Incident with radiography source resulting in severe radiation burns. Pressure buildup led to an explosive mechanical failure.

Spread of contamination to an area not expected by design. Near accident caused by fire resulting in loss of safety systems at the nuclear power station. Widespread health and environmental effects. External release of a significant fraction of reactor core inventory. Spherical fuel pebble became lodged in the pipe used to deliver fuel elements to the reactor.

More than workers were exposed to doses of up to millirem per day radiation. Melting of one channel of fuel in the reactor with no release outside the site. Damaged fuel integrity, extensive corrosion damage of fuel cladding and release of radioactivity. Total loss of coolant led to a power excursion and explosion of experimental reactor. Graphite debris partially blocked a fuel channel causing a fuel element to melt and catch fire.

Error by a worker at a United Nuclear Corporation fuel facility led to an accidental criticality. Due to inadequate cooling a damaged uranium fuel rod caught fire and was torn in two.