4. Where does Nuclear or Radiological Accident occur?

Radiation is used in medicine, the military and industry.

The main users of man-made radiation include:

  • nuclear reactors and their supporting facilities such as fuel preparation plants; 
  • medical facilities such as hospitals and pharmaceutical facilities; 
  • research and teaching institutions; 
  • facilities involved in nuclear weapons production. 

More than 400 Nuclear Power Reactors are in operation around the world (see https://cnpp.iaea.org/pages/index.htm ).

The most serious accident in the history of the nuclear industry occurred on 26 April 1986, at Unit 4 of the Chernobyl nuclear power plant in the former Ukrainian Republic of the Union of Soviet Socialist Republics, near the common borders of Belarus, the Russian Federation and Ukraine. Major releases of radionuclides from the Chernobyl reactor continued for ten days following the explosion on 26 April. 

These included radioactive gases, condensed aerosols and fuel particles. The total release of radioactive material was about 14×1018 Bq. More than 200,000 square kilometres of Europe were contaminated with levels of 137Cs above 37 kBq/m2. Much of this area was within the three most affected countries, Belarus, Russia and Ukraine. More than 100,000 people in Belarus, Ukraine and Russia were evacuated from the contaminated area and about 5 million were exposed. In France, Germany, Poland and other European countries, radiation protection measures were implemented. 
Acute radiation syndrome due to high exposure (ARS) was diagnosed in 134 emergency workers exposed from 1 to 16 Gy of whole-body irradiation. Twenty eight patients died within three months after exposure. Thyroid cancer in those exposed to 131I at a young age is recognised as a major health effect of the accident confirmed by the findings of many national and international studies. Twenty five years after the accident, nearly 6,000 cases of thyroid cancer have been diagnosed in persons exposed at the age of 0-18 in Belarus, Russia and Ukraine. See more about radiological hazards here .

The Fukushima-1 (Dai-ichi) nuclear accidents were a series of ongoing equipment failures and releases of radioactive materials at the Fukushima-1 Nuclear Power Plant, as a result of the 9.0 magnitude earthquake and tsunami on 11 March 2011. The nuclear plant was flooded by tsunami waves. Evidence soon arose of a partial core meltdown in reactors 1, 2, and 3; hydrogen explosions destroyed the upper cladding of the buildings housing reactors 1, 3, and 4; an explosion damaged the containment inside reactor 2; and multiple fires broke out at reactor 4. Despite being initially shut down, reactors 5 and 6 began to overheat. Fuel rods stored in pools in each reactor building began to overheat, as water levels in the pools dropped. 
The total discharge amounts from the reactors of Fukushima-1 NPP were estimated as 0.16 EBq for 131I and 0.015 EBq 137Cs.
Approximately 7,800 emergency workers were exposed to about 7.7 mSv on average. Thirty people were recorded as receiving doses over 100 mSv. 
Three workers are reported to have suffered suspected radiation burns on their feet/legs from inadvertent exposure to heavily contaminated water in a turbine basement. 
To avert potential radiation exposure to the public, the Japanese authorities took the precautionary measure of instructing those within the first 3 km, then 10 km and finally 20 km of the plant to evacuate, and those between 20 km and 30 km to take shelter and prepare to evacuate. More than 70,000 people have been evacuated since the incident.

The worst commercial accident in the United States occurred at the Three Mile Island nuclear station in 1979. As a result of equipment failures and operator error, a valve that was stuck open allowed coolant water that covered the reactor core to escape from the reactor system for over two hours. 
This radioactive water, nearly a million gallons, ended up on the basement floors of the containment building and auxiliary buildings. The loss of coolant water in the reactor core continued to the point that the fuel was no longer submerged in water. Without the cooling provided by the water, the cladding and some of the fuel pellets melted. Large quantities of radioactive material were released into the containment building.

Radiological accidents are initiated by lost radiation sources, accidents during transportation of radioactive sources or materials, equipment or human errors in radiation sources operation.

One of the most severe radiological accidents took place in September 1987 at Goiania, Brazil. A radiotherapy unit had been abandoned in a clinic, which was being demolished. The unit had a source consisting of 
5×1013 Bq of cesium-137, sealed within two nested stainless steel containers to form a 5-cm diameter capsule.
Two individuals dismantled the unit and extracted the source, before taking it home and opening it. On 21 September the source material was removed and distributed among several persons, some of whom spread it on their skin. Of the 112,800 or so people who were examined, 129 were found to be contaminated and 9 persons died.