Major Nuclear Power Disasters

As of now, three major accidents have been considered as massive disasters with high INES (International Nuclear Event Scale) rating in 63 years of the nuclear power history. Of the accidents, the Chernobyl disaster in 1986 claimed 31 lives due to high-level radiation. It is evident that the casualty is much less in case of nuclear power generation than other power generation facilities like coal, gas and hydro-based plants. Two major aspects, which are interlinked as well, played role in favor of nuclear technology in electricity generation. The first reason might be the higher destructive capacity of nuclear reactors that prompted adopting high-level of safety measures at nuclear power plants and the second is the investment for ensuring safety, which is still competitive for electricity generation.

TWY: Tera Watt Year

Source: ‘The Revenge of Gaia’ by James Lovelock page 102.

In electricity generation industry, it has been told that accidents at the power plants are mainly caused by the management’s profiteering attitude, leaving public safety issues ignored. Every accident at nuclear power premises prompted nuclear scientists and engineers to introduce additional safety measures that also increased the amount of capital investments. The latest safety upgradation schemes were introduced after the Fukushima disaster that occurred in 2011, following a 15-meter tsunami. No casualty or health effect was found after the accident at the nuclear power plant although 2,000 people were killed, and 1,200 others went missing for the tsunami. But it has been pointed out that bureaucratization of the managements for operation and maintenance of nuclear power plants is a major threat for public safety.

Fukushima Accident(Updated October 2017)

Following a major earthquake, a 15-meter tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on 11 March 2011. All three cores largely melted in the first three days.

The accident was rated 7 on the INES scale, due to high radioactive releases over days 4 to 6, eventually a total of some 940 PBq (I-131 eq). PBq or petabecquerel is a unit of radiation.

Four reactors with 2,719MW net capacity were written off due to damage in the accident.

After two weeks, the three reactors (units 1-3) were stable with water addition and by July they were being cooled with recycled water from the new treatment plant.Official 'cold shutdown condition' was announced in mid-December.

Apart from cooling, the basic ongoing task was to prevent release of radioactive materials, particularly in contaminated water leaked from the three units.

In its first report published in May 2013 and a follow-up report in October 2015, the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) said that the radiation exposure following the nuclear accident at Fukushima Daiichi did not cause any immediate health effects. It is unlikely to be able to attribute any health effects in the future among the public and majority of workers, the UNSCEAR reports said that prepared following detailed studies by 80 international experts.

Allegations have that the Fukushima Daiichi nuclear power plant’s operator, Tokyo Electric Power Company Holdings Inc, ignored warnings of the tsunami with such magnitude and did not develop protections for the power plant.

Chernobyl Accident 1986 (Updated November 2016)

The Chernobyl accident on 26 April 1986 in Ukraine, a soviet of former USSR, was the result of a flawed reactor design that was operated with inadequately trained personnel.

The resulting steam explosion and fires released at least 5% of the radioactive reactor core into the atmosphere and downwind – some 5200 PBq (I-131 eq).

A total of 31 people, all are the workers at the plant, died of acute radiation poisoning.

UNSCEAR said that apart from increased thyroid cancers, ‘there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident.’

In 2011, Chernobyl was officially declared a tourist attraction.

The Chernobyl nuclear disaster was the product of a flawed Soviet reactor design coupled with serious mistakes made by the plant operators. It was a direct consequence of Cold War isolation and the resulting lack of any safety culture.

The accident destroyed the Chernobyl 4 reactor, killing 30 operators and firemen within three months and several further deaths later. One person was killed immediately and a second died in hospital soon after injuries received. Another person is reported to have died at the time from a coronary thrombosis. Acute radiation syndrome (ARS) was originally diagnosed in 237 people onsite and involved with the clean-up and it was later confirmed in 134 cases. Of these, 28 people died because of ARS within a few weeks of the accident. Nineteen more subsequently died between 1987 and 2004 but their deaths cannot necessarily be attributed to radiation exposure.

Nobody offsite suffered from acute radiation effects although a large proportion of the childhood thyroid cancers diagnosed since the accident are likely to be due to intake of radioactive iodine fallout. Furthermore, large areas of Belarus, Ukraine, Russia, and beyond were contaminated in varying degrees.

The Chernobyl disaster was a unique event and the only accident in the history of commercial nuclear power where radiation-related fatalities occurred. The design of the reactor was unique and in that respect the accident was thus of little relevance to the rest of the nuclear industry outside the then Eastern Block. However, it led to major changes in safety culture and in industry cooperation, particularly between East and West before the end of the Soviet Union. Former President Gorbachev said that the Chernobyl accident was a more important factor in the fall of the Soviet Union than Perestroika – his program of liberal reform.

Three Mile Island Accident

A cooling malfunction caused part of the core to melt in the #2 reactor on 28 March 1979 at Three Mile Island nuclear power plant in USA. The TMI-2 reactor was destroyed.

Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local people.

There were no injuries or adverse health effects from the Three Mile Island accident.

The Three Mile Island power station is near Harrisburg, Pennsylvania in USA. It had two pressurized water reactors. One PWR was of 800 MW (775 MW net) and entered service in 1974. It remains one of the best-performing units in USA. Unit 2 was of 906 MW (880 MW net) and almost brand new.

The accident to unit 2 happened at 4 am on 28 March 1979 when the reactor was operating at 97% power. It involved a relatively minor malfunction in the secondary cooling circuit which caused the temperature in the primary coolant to rise. This in turn caused the reactor to shut down automatically. Shut down took about one second. At this point a relief valve failed to close, but instrumentation did not reveal the fact, and so much of the primary coolant drained away that the residual decay heat in the reactor core was not removed. The core suffered severe damage as a result. The operators were unable to diagnose or respond properly to the unplanned automatic shutdown of the reactor. Deficient control room instrumentation and inadequate emergency response training proved to be root causes of the accident. The chain of events during the Three Mile Island accident within seconds of the shutdown, the pilot-operated relief valve (PORV) on the reactor cooling system opened, as it was supposed to. About 10 seconds later it should have closed. But it remained open, leaking vital reactor coolant water to the reactor coolant drain tank.

Source: World Nuclear Association

Manjurul Ahsan Shuvro;

Dhaka-Based Reporter with Focus in Energy Sector