Chapter 35: Chernobyl

This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on September 16, 2012.

Exactly seven years and twenty eight days after the Three Mile Island accident in the United States, the Chernobyl accident, the most serious accident in the history of the nuclear industry, occurred on April 26, 1986 at Unit 4 (RBMK-1000 Reactor) of the Chernobyl nuclear power plant in the former Ukrainian Republic of the Soviet Union.  The explosions completely shattered the Chernobyl reactor vessel and triggered fire that continued for 10 days.  As a result, large amounts of radioactive materials were released into the environment and it changed the global opinion about the safety of nuclear energy. Slide1Here is a brief description of RBMK reactor:  The RBMK is an early Generation II reactor and the oldest commercial reactor design still in wide operation; it features a number of design and safety flaws (such as graphite-tipped control rods, a dangerous positive void coefficient and instability at low power levels) that have since been rectified in newer designs.  The reactor pit is made of reinforced concrete and has dimensions 21.6×21.6×25.5 meters. It houses the vessel of the reactor, made of a cylindrical wall and top and bottom metal plates. The vessel contains the graphite stack and is filled with a helium-nitrogen mixture for providing an inert atmosphere for the graphite and for mediation of heat transfer from the graphite to the coolant channels.

The Chernobyl nuclear power plant was built in the wooded marshlands of northern Ukraine, approximately 130 km north of Kiev. Its first reactor went online in 1977, the second in 1978, third in 1981, and fourth in 1983; two more were planned for construction.

This area of Ukraine is described as Belarusian-type woodland with a low density.  A small town, Pripyat, was also built near the Chernobyl nuclear power plant to house the workers and their families.  There were 49,000 inhabitants living in this town.  The old town Chernobyl, which had a population of 12,500, is about 15 km to the southeast of the complex.  Within a 30 km radius of the plant, the total population was between 115,000 and 135,000.

The plan was to shut down the plant for some routine maintenance on April 25, 1986. During the shutdown, technicians were also going to run a test. The test was to determine whether, in case of a power outage, the turbines could produce enough energy to keep the cooling system running until the backup generators came online.  The shutdown and test began as planned at 1 a.m. on April 25th. To get accurate results from the test, the operators turned off several of the safety systems, which turned out to be a disastrous decision. In the middle of the test, the shutdown had to be delayed nine hours because of a high demand for power in Kiev. The shutdown and test continued again at 11:10 p.m. on the night of April 25th.Slide2Just after 1 a.m. on April 26th, the reactor’s power dropped suddenly, causing a potentially dangerous situation. The operators tried to compensate for the low power but the reactor went out of control. If the safety systems had remained on, they would have fixed the problem; however, they were not. The reactor exploded at 1:23 a.m.  However, the world discovered the accident two days later, on April 28th, when operators of the Swedish Forsmark nuclear power plant in Stockholm registered unusually high radiation levels near their plant. When other plants around Europe began to register similar high radiation readings, they contacted the Soviet Union to find out what had happened. The Soviets denied any knowledge about a nuclear disaster until 9 p.m. on April 28th, when they announced to the world that one of the reactors had been “damaged.”

The Soviets, while trying to keep the nuclear disaster a secret, they were also trying to clean it up.  At first they poured water on the many fires then they tried to put them out with sand and lead and then nitrogen. It took nearly two weeks to put the fires out. Citizens in the nearby towns were told to stay indoors. Pripyat was evacuated (45,000 residents) on April 27th, the day after the disaster had begun.  By 14 May, some 116,000 people that had been living within a 30 kilometre radius had been evacuated and later relocated. About 1000 of these returned unofficially to live within the contaminated zone.  The town of Chernobyl wasn’t evacuated until May 2, six days after the explosion.  Most of those evacuated received radiation doses of less than 50 mSv, although a few received 100 mSv or more.

Here is a summary of the conclusions published by the World Nuclear Association:

  • The Chernobyl accident in 1986 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 percent of the radioactive reactor core into the atmosphere and downwind;
  • Two Chernobyl plant workers died on the night of the accident, and a further 28 people died within a few weeks as a result of acute radiation poisoning;
  • UNSCEAR says 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”; and
  • Resettlement of areas from which people were relocated is ongoing.

The casualties included firefighters who attended the initial fires on the roof of the turbine building. All these were put out in a few hours, but radiation doses on the first day were estimated to range up to 20,000 millisieverts (mSv), causing 28 deaths – six of which were firemen – by the end of July 1986.

According to a report published on the subject of Chernobyl’s Legacy, an estimated 350 000 emergency and recovery operation workers, including army, power plant staff, local police and fire services, were initially involved in containing and cleaning up the accident in 1986–1987.  Among them, about 240 000 recovery operation workers took part in major mitigation activities at the reactor and within the 30-km zone surrounding the reactor. Later, the number of registered “liquidators” rose to 600 000, although only a small fraction of these were exposed to high levels of radiation.Slide3More than five million people live in areas of Belarus, Russia, and Ukraine that are classified as “Contaminated” with radionuclides due to the Chernobyl accident.  Among them, about 400,000 people lived in more contaminated areas – Classified by Soviet authorities as areas of strict radiation control.  Of this population, 116,000 people were evacuated in the spring and summer of 1986 from the area surrounding the Chernobyl power plant (Designed the “Exclusion Zone”) to non-contaminated areas.  Another 220,000 people were relocated in subsequent years.

Unfortunately, reliable information about the accident and the resulting dispersion of radioactive material was initially unavailable to the affected people in what was then the Soviet Union and remained inadequate for years following the accident. This failure and delay led to widespread distrust of official information and the mistaken attribution of many ill health conditions to radiation exposure.

According to the report published by the Chernobyl Forum, the Chernobyl nuclear accident, and government policies adopted to cope with its consequences, imposed huge costs on the Soviet Union and three successor countries, Belarus, the Russian Federation, and Ukraine.  Although these three countries bore the brunt of the impact, given the spread of radiation outside the borders of the Soviet Union, other countries (like Scandinavia, for instance).

The costs of the Chernobyl nuclear accident can only be calculated with a high degree of estimation, given the non-market conditions prevailing at the time of the disaster and the high inflation and volatile exchange rates of the break-up of the Soviet Union in 1991.  However, the magnitude of the impact is clear from a variety of government estimates from the accident, over two decades, at hundreds of billions of dollars.Slide4The scale of the burden is clear from the wide range of costs incurred, both direct and indirect:

  • Direct damage caused by the accident;
  • Expenditures related to:
    • Actions to seal off the reactor and mitigate the consequences in the exclusion zone;
    • Resettlement of people and construction of new housing and infrastructure to accommodate them;
    • Social protection and health care provided to the affected population;
    • Research on environment, health and production of clean food;
    • Radiation monitoring of the environment; and
    • Radioecological improvement of settlements and disposal of radioactive waste.
  • Indirect losses relating to the opportunity cost of removing agricultural land and forests from use and the closure of agricultural and industrial facilities; and
  • Opportunity costs, including the additional costs of energy resulting from the loss of power from the Chernobyl nuclear plant and the cancellation of Belarus’s nuclear power programme.

Coping with the impact of the disaster has placed a huge burden on national budgets. In Ukraine, 5–7 percent of government spending each year is still devoted to Chernobyl-related benefits and programmes.  In Belarus, government spending on Chernobyl amounted to 22.3 percent of the national budget in 1991, declining gradually to 6.1 percent in 2002.  Total spending by Belarus on Chernobyl between 1991 and 2003 is estimated at more than US $13 billion.

This massive expenditure has created an unsustainable fiscal burden, particularly for Belarus and Ukraine.  Although capital intensive spending on resettlement programmes has been curtailed or concluded, large sums continue to be paid out in the form of social benefits for as many as 7 million recipients in the three countries.  With limited resources, governments thus face the task of streamlining Chernobyl programmes to provide more focused and targeted assistance with an eye to helping those groups that are most at risk from health hazards or socio-economic deprivation.

For the last two decades, attention has been focused on investigating the association between exposure caused by radionuclides released in the Chernobyl accident and late effects, in particular thyroid cancer in children. Doses to the thyroid received in the first few months after the accident were particularly high in those who were children and adolescents at the time in Belarus, Ukraine and the most affected Russian regions and drank milk with high levels of radioactive iodine. By 2005, more than 6,000 thyroid cancer cases had been diagnosed in this group, and it is most likely that a large fraction of these thyroid cancers is attributable to radioiodine intake. It is expected that the increase in thyroid cancer incidence due to the Chernobyl accident will continue for many more years, although the long-term increase is difficult to quantify precisely.Slide5Among the 106 patients surviving radiation sickness, complete normalization of health took several years. Many of those patients developed clinically significant radiation-induced cataracts in the first few years after the accident. Over the period 1987-2006, 19 survivors died for various reasons; however, some of these deaths were due to causes not associated with radiation exposure.

Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age, and some indication of an increased leukaemia and cataract incidence among the workers, there is no clearly demonstrated increase in the incidence of solid cancers or leukaemia due to radiation in the exposed populations. Neither is there any proof of other non-malignant disorders that are related to ionizing radiation. However, there were widespread psychological reactions to the accident, which were due to fear of the radiation, not to the actual radiation doses.

There is a tendency to attribute increases in the rates of all cancers over time to the Chernobyl accident, but it should be noted that increases were also observed before the accident in the affected areas. Moreover, a general increase in mortality has been reported in recent decades in most areas of the former Soviet Union, and this must be taken into account when interpreting the results of the accident-related studies.

The impact of the accident on agricultural practices, food production and use and other aspects of the environment has been and continues to be much more widespread than the direct health impact on humans.  Several techniques of soil treatment and decontamination to reduce the accumulation of radioactivity in agricultural produce and cow’s milk and meat have been experimented with positive results in some cases.

Nevertheless, within the former Soviet Union large areas of agricultural land are still excluded from use and are expected to continue to be so for a long time. In a much larger area, although agricultural and dairy production activities are carried out, the food produced is subjected to strict controls and restrictions of distribution and use.Slide6Similar problems of control and limitation of use, although of a much lower severity, were experienced in some countries of Europe outside the former Soviet Union, where agricultural and farm animal production were subjected to restrictions for variable durations after the accident. Most of these restrictions have been lifted several years ago. However, there are still today some areas in Europe where restrictions on slaughter and distribution of animals are in force. This concerns, for example, several hundreds of thousands of sheep in the United Kingdom and large numbers of sheep and reindeer in some Nordic countries.

A kind of environment where special problems were and continue to be experienced is the forest environment. Because of the high filtering characteristics of trees, deposition was often higher in forests than in other areas. An extreme case was the so-called “red forest” near to the Chernobyl site where the irradiation was so high as to kill the trees which had to be destroyed as radioactive waste. In more general terms, forests, being a source of timber, wild game, berries and mushrooms as well as a place for work and recreation, continue to be of concern in some areas and are expected to constitute a radiological problem for a long time.

Water bodies, such as rivers, lakes and reservoirs can be, if contaminated, an important source of human radiation exposure because of their uses for recreation, drinking and fishing. In the case of the Chernobyl accident this segment of the environment did not contribute significantly to the total radiation exposure of the population. It was estimated that the component of the individual and collective doses that can be attributed to the water bodies and their products did not exceed 1 or 2 percent of the total exposure resulting from the accident. The contamination of the water system has not posed a public health problem during the last decade; nevertheless, in view of the large quantities of radioactivity deposited in the catchment area of the system of water bodies in the contaminated regions around Chernobyl, there will continue to be for a long time a need for careful monitoring to ensure that washout from the catchment area will not contaminate drinking-water supplies.

Outside the former Soviet Union, no concerns were ever warranted for the levels of radioactivity in drinking water. On the other hand, there are lakes, particularly in Switzerland and the Nordic countries, where restrictions were necessary for the consumption of fish. These restrictions still exist in Sweden, for example, where thousands of lakes contain fish with a radioactivity content which is still higher than the limits established by the authorities for sale on the market.Slide7The lessons that could be learned from the Chernobyl accident were, therefore, numerous and encompassed all areas, including reactor safety and severe accident management, intervention criteria, emergency procedures, communication, medical treatment of irradiated persons, monitoring methods, Radioecological processes, land and agricultural management, public information, etc.

However, the most important lesson learned was probably the understanding that a major nuclear accident has inevitable transboundary implications and its consequences could affect, directly or indirectly, many countries even at large distances from the accident site. This led to an extraordinary effort to expand and reinforce international co-operation in areas such as communication, harmonisation of emergency management criteria and co-ordination of protective actions. Major improvements were achieved in this decade and important international mechanisms of co-operation and information were established, such as the international conventions on early notification and assistance in case of a radiological accident, by the International Atomic Energy Agency (IAEA) and the European Commission (EC), the International Nuclear Emergency Exercises (INEX) programme, by the Nuclear Energy Agency (NEA), the International Accident Severity Scale (INES), by the IAEA and NEA and the international agreement on food contamination, by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO).

At the national level, the Chernobyl accident also stimulated authorities and experts to a radical review of their understanding of and attitude to radiation protection and nuclear emergency issues. This prompted many countries to establish nationwide emergency plans in addition to the existing structure of local emergency plans for individual nuclear facilities.  In the scientific and technical area, besides providing new impetus to nuclear safety research, especially on the management of severe nuclear accidents, this new climate led to renewed efforts to expand knowledge on the harmful effects of radiation and their medical treatment and to revitalize radioecological research and environmental monitoring programmes. Substantial improvements were also achieved in the definition of criteria and methods for the information of the public, an aspect whose importance was particularly evident during the accident and its aftermath.

According to the World Nuclear Association, modifications have been made to overcome deficiencies in all the RBMK reactors still operating. In these, originally the nuclear chain reaction and power output could increase if cooling water was lost or turned to steam, in contrast to most Western designs. It was this effect which led to the uncontrolled power surge that led to the destruction of Chernobyl 4. All of the RBMK reactors have now been modified by changes in the control rods, adding neutron absorbers and consequently increasing the fuel enrichment from 1.8 to 2.4 percent U-235, making them very much more stable at low power. Automatic shut-down mechanisms now operate faster, and other safety mechanisms have been improved. Automated inspection equipment has also been installed. A repetition of the 1986 Chernobyl accident is now virtually impossible, according to a German nuclear safety agency report.Slide8While no-one in the West was under any illusion about the safety of early Soviet reactor designs, some lessons learned have also been applicable to Western plants. Certainly the safety of all Soviet-designed reactors has improved vastly. This is due largely to the development of a culture of safety encouraged by increased collaboration between East and West, and substantial investment in improving the reactors.


  1. Wikipedia – RBMK Reactor;
  2. Wikipedia – Generation II Reactors;
  3. Wikipedia – Void Coefficient;
  4. Wikipedia – Reactor Type;
  5. Wikipedia – Reinforced Concrete;
  6. 20th Century History – Chernobyl Nuclear Accident;
  7. World Nuclear Association – Chernobyl Accident 1986;
  8. Chernobyl’s Legacy – Health, Environmental and Socio-Economical Impacts;
  9. United Nations Scientific Committee on the Effects of Atomic Radiation; and
  10. NEA Chernobyl Ten Years on.

Chapter 36