The Chernobyl disaster

INTRODUCTION

The Chernobyl disaster was a nuclear reactor accident in the Chernobyl Nuclear Power Plant in the Soviet Union (now Northern Ukraine). It was the worst nuclear power plant accident in history and the only instance of level 7 on the International Nuclear Event Scale, resulting in a severe release of radioactivity into the environment following a massive power excursion which destroyed the reactor. Two people died in the initial steam explosion, but most deaths from the accident were attributed to fallout.

On 26 April 1986 at 01:23:44 a.m. reactor number four at the Chernobyl plant, near Pripyat in the Ukrainian SSR, exploded. Further explosions and the resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area. Four hundred times more fallout was released than had been by the atomic bombing of Hiroshima.

The plume drifted over extensive parts of the western Soviet Union, Eastern Europe, Western Europe, Northern Europe, and eastern North America. Large areas in Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. According to official post-Soviet data, about 60% of the radioactive fallout landed in Belarus.

The accident raised concerns about the safety of the Soviet nuclear power industry, slowing its expansion for a number of years, while forcing the Soviet government to become less secretive. The now-independent countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. It is difficult to accurately tell the number of deaths caused by the events at Chernobyl, as the Soviet-era cover-up made it difficult to track down victims. Lists were incomplete, and Soviet authorities later forbade doctors to cite "radiation" on death certificates.

The 2005 report prepared by the Chernobyl Forum, led by theInternational Atomic Energy Agency (IAEA) and World Health Organization (WHO), attributed 56 direct deaths (47 accident workers, and nine children with thyroid cancer, and estimated that there may be 4,000 extra cancer deaths among the approximately 600,000 most highly exposed people. Although the Chernobyl Exclusion Zone and certain limited areas will remain off limits, the majority of affected areas are now considered safe for settlement and economic activity.

THE ACCIDENT

The Chernobyl nuclear power plant was one of the largest in the USSR. It was located just outside of the town of Pripyat', about 18 km (11 mi) northwest of the town of Chernobyl'. The plant was only 16 km (10 mi) from the border between the Ukrainian and Belorussian republics and roughly 110 km (70 mi) north of Kyiv (Kiev), the capital and largest city of Ukraine. Construction of the plant began in the 1970s, with reactor No. 1 commissioned in 1977, followed by No. 2 (1978), No. 3 (1981), and No. 4 (1983). Each reactor had an electricity-generating capacity of 1,000 megawatts, and the four together produced about 10 percent of Ukraine's electricity at the time of the accident. Two more reactors (No. 5 and No. 6, also capable of producing 1,000 megawatts each) were under construction at the time of the accident.

In the early morning hours of April 26, 1986, reactor No. 4 was operating at very low capacity (6 to 7 percent) during a planned shutdown. Plant personnel intended to monitor the performance of turbine generators, which supplied electric power for the plant's own operation, during a changeover from standard to a backup source of power. The reactor's design made it unstable at low power, and the operators were careless about safety precautions during the test. After a sudden power surge, two explosions destroyed the reactor core and blasted a large hole in the roof of the reactor building. Radioactive debris moved up through this hole to heights of 1 km (0.6 mi), carried by a strong updraft. Fires caused by the explosion and the heat of the reactor core fed the updraft.

An estimated 100 to 150 million curies of radiation (primarily radioactive isotopes of iodine and cesium) escaped into theatmosphere before cleanup crews were able to bring the fires under control and stabilize the situation some two weeks later. Initially, prevailing winds carried the radioactivity northwest from the plantacross Belorussia and into Poland and Sweden, where heightened radiation levels detected on April 28 first brought the accident to the world's attention. Subsequently, from May 1 to 5, wind patterns shifted so that the bulk of radioactivity was carried more directly north and northeast, over Belorussia and southwestern Russia.

After the explosion, firefighters and other workers arrived on the scene in an attempt to contain the blast. To reduce emissions, the team bombarded the reactor with 5,000 metric tons of shielding material consisting of lead, boron, sand, and clay. A second concrete foundation was constructed under the reactor to prevent contamination of groundwater. Finally, workers erected an enormous concrete-and-steel shell or “sarcophagus” over the damaged reactor to prevent radioactive materials, including gases and dust, from escaping. Initially, Soviet officials placed the death toll at 2 (both workers killed during the explosion at the No. 4 reactor) but by mid-August revised the figure to 31, reflecting deaths of workers from acute radiation exposure during the cleanup.

By mid-July, roughly three months after the accident, containment and cleanup had proceeded to the point where the plant's management had moved back into the administration building just 300 m (about 1,000 ft) from the No. 4 reactor. In addition to reducing the radiation threat, a key objective to the cleanup effort was resumption of electric power generation at Chernobyl' before the onset of winter. The No. 1 and No. 2 reactors, in fact, were returned to service in November 1986 and the slightly damaged No. 3 unit was restarted in December 1987.

EVACUATION

More than 100,000 people were evacuated during the first few weeks after the accident. Evacuation of Pripyat' (where 35,000 people lived at the time of the accident) and the immediate surrounding area began roughly 36 hours after the accident, on the afternoon of April 27. Evacuation within a larger, officially designated evacuation zone of 2800 sq km (1100 sq mi), including parts of Belorussia began on May 3. That area became known as the '30-km zone' because it is a circle with a 30-km (19-mi) radius from Pripyat'. At least 50,000 people were relocated in Ukraine and 25,000 in Belorussia during this second-stage evacuation, which continued into June.

As officials, especially in Belorussia, determined that areas of serious contamination extended well beyond the official evacuation zone, additional people were relocated. Fifty thousand people were evacuated from areas outside the 30-km zone in Belorussia in 1986 and 1987, over 30,000 more between 1991 and 1993, and roughly 50,000 in Ukraine over the period from 1991 to 1996. The total number of people evacuated in Ukraine and Belorussia as a result of Chernobyl' now appears to exceed 200,000.

AFTERMATH

The principal environmental effect of the Chernobyl' accident has been the accumulation of radioactive fallout in the upper layers of soil, where it has destroyed important farmland. The second most important impact has been the threat to surface water and groundwater. The cleanup in some of the most heavily contaminated areas within the evacuation zone, such as Pripyat', involved thestripping and burying of topsoil and vegetation, the sealing of wells, and the building of structures designed to prevent surface water from entering streams and rivers that drain into the Dnieper River system, which provides Kyiv's water supply.

By most measures, the country most seriously affected by the accident is Belarus (which changed its name from Belorussia after it, along with the other Soviet republics, became independent with the collapse of the USSR in 1991). Almost 20 percent of the republic's farmland was removed from production during the years immediately after the accident. Half of the vast 27,850-sq km (10,750-sq mi) area described as being 'seriously contaminated' by radiation (with levels of radioactive cesium in topsoil exceeding 5 curies) is in Belarus. The regions commonly identified as experiencing the greatest contamination include the oblasts (regions) of Homyel', Mahilyow, and Brest in southern and eastern Belarus; Kyiv, Zhytomyr, and Chernihiv in northern Ukraine; and Bryansk in southwestern Russia.

Effects on public health have been more difficult to determine and are subject to considerable controversy. It is not always clear which health problems are caused directly by radiation and which are caused by poor nutrition, the general low level of health, and the anxiety and stress produced by fear of radiation exposure. These issues surround the debate over the causes of higher death rates among the more than half a million workers who participated in the Chernobyl' cleanup.

However, at least one type of cancer can be attributed directly to Chernobyl'. There has been a significant rise in the incidence of thyroid cancer among children in the areas where radiation levels are highest. Thyroid cancer rates in Homyel' Oblast, for example, increased 22-fold from 1986 through 1990 compared to the period from 1981 through 1985.

Also, after the accident several key officials in the Soviet nuclear power industry were dismissed, punished, or both, and a new Ministry of Nuclear Power was created in 1986. Before then, officials in the general electric power ministry had overseen nuclear power. Chernobyl' also called into question the basic safety of nuclear power in both the USSR and several Eastern European countries whose power plants contained reactors based on the RBMK reactor design used at Chernobyl'. (In the RBMK design, there is no containment shell, the graphite blocks used to moderate the fission reaction are flammable, and excess steam in the reactor core will cause the nuclear reaction to increase). As a consequence, international organizations, such as the International Atomic Energy Agency, became involved in programs to improve safety procedures and upgrade the design of RBMK reactors in the USSR and Eastern Europe.

Earlier in 1990 the Ukrainian parliament had voted to close the Chernobyl' plant permanently within five years, but closure was repeatedly postponed because of the country's shortage of electricity-generating capacity. After a turbine fire in October 1991, the No. 2 reactor at Chernobyl' was shut down, leaving only two of the original four reactors at the plant in service. Reflecting mounting safety concerns in the international community, an agreement was concluded in April 1996 between the Ukrainian government and the G-7 countries (Group of Seven major industrial nations) to decommission the Chernobyl' plant by the year 2000. In conjunction with the agreement, the G-7 countries pledged $300 million to finance programs to strengthen the sarcophagus, which some fear may collapse, and for additional cleanup work. In November 1996, as part of the schedule for the decommissioning, the No. 1 reactor at Chernobyl' was taken out of service, leaving only the third unit operational. Finally, in December 2000 the plant was totally shut down.

CHERNOBYL AFTER THE DISASTER

Following the accident, questions arose on the future of the plant and its eventual fate. All work on the unfinished reactors 5 and 6 was halted three years later. However, the trouble at the Chernobyl plant did not end with the disaster in reactor 4. The damaged reactor was sealed off and 200 metres (660 ft) of concrete was placed between the disaster site and the operational buildings. The Ukrainian government continued to let the three remaining reactors operate because of an energy shortage in the country. A fire broke out in the turbine building of reactor 2 in 1991; the authorities subsequently declared the reactor damaged beyond repair and had it taken offline. Reactor 1 was decommissioned in November 1996 as part of a deal between the Ukrainian government and international organizations such as the IAEA to end operations at the plant. On 15 December 2000, then-President Leonid Kuchma personally turned off Reactor 3 in an official ceremony, effectively shutting down the entire plant transforming the Chernobyl plant from energy producer to energy consumer.

CHERNOBYL TODAY

The Chernobyl reactor is now enclosed in a large concrete sarcophagus which was built quickly to allow continuing operation of the other reactors at the plant. However, the structure is not strong or durable. Some major work on the sarcophagus was carried out in 1998 and 1999. Some 200 tonnes of highly radioactive material remains deep within it, and this poses an environmental hazard until it is better contained.

A New Safe Confinement structure will be built by the end of 2011, and then will be put into place on rails. It is to be a metal arch 105 meters high and spanning 257 metres, to cover both unit 4 and the hastily-built 1986 structure. The Chernobyl Shelter Fund, set up in 1997, has received €810 million from international donors and projects to cover this project and previous work. It and the Nuclear Safety Account, also applied to Chernobyl decommissioning, are managed by the European Bank for Reconstruction and Development (EBRD).

As of 2006, some fuel at units 1 to 3 remained in the reactors, most of which is in each unit's cooling pond, as well as some material in a small interim spent fuel storage facility pond (ISF-1).

In 1999 a contract was signed for construction of a radioactive waste management facility to store 25,000 used fuel assemblies from units 1–3 and other operational wastes, as well as material from decommissioning units 1–3 (which will be the first RBMK units decommissioned anywhere). The contract included a processing facility, able to cut the RBMK fuel assemblies and to put the material in canisters, which will be filled with inert gas and welded shut. They will then be transported to the dry storage vaults in which the fuel containers would be enclosed for up to 100 years. This facility, treating 2500 fuel assemblies per year, would be the first of its kind for RBMK fuel. However, after a significant part of the storage structures had been built, technical deficiencies in the concept emerged, and the contract was terminated in 2007. The interim spent fuel storage facility (ISF-2) will now be completed by others by mid 2013.

Another contract has been let for a Liquid radioactive Waste Treatment Plant, to handle some 35,000 cubic meters of low- and intermediate-level liquid wastes at the site. This will need to be solidified and eventually buried along with solid wastes on site.

In January 2008 the Ukraine government announced a 4-stage decommissioning plan which incorporates the above waste activities and progresses towards a cleared site.

SARCOPHAGUS

The Chernobyl Unit 4 post accident containment structure, more commonly known as the "sarcophagus" was completed in November 1986. The sarcophagus was built in extremely hazardous conditions in order to isolate and contain the remains of the damaged reactor which contains over 400kg of plutonium and more than 100 tons of nuclear fuel. 

Designed to last 30 years, it now suffers from approximately 300 square yards of cracks and holes along with other weaknesses which have arisen due to both the speed of construction and the conditions under which it was built. The design of the sarcophagus did not allow for potential earthquake stresses and both Ukrainian and Western scientists say it could collapse in a severe earthquake releasing radioactive dust. In March 1996, the Ukrainian Environment Minister stated "There is a real danger that as a result of thermal chemical migration of nuclear fuel deep in the debris of the reactor of the fourth power unit, a critical concentration may arise that will lead to a speedy heating and a thermal blast", however, not all experts agree with this analysis.

DANGEROUS REACTORS STILL OPERATING

Since 1986 there has not been any significant improvement in nuclear safety in Central and Eastern Europe (CEE) or the former Soviet Union (FSU). This is a sentiment reiterated in a publication by the Department of Energy Office of Energy Intelligence, which states.

"Many Soviet designed reactors operating in the successor states to the Soviet Union pose significant safety risks because of inherent design deficiencies, deteriorating economies, political turmoil and weak regulatory oversight. As a class, these reactors continue to experience serious incidents, raising the spectre of another accident akin to Chernobyl"

The report concludes that the four worst reactors in the region are Chernobyl (Ukraine), Kozloduy (Bulgaria), Kola (Russia) and Iganalina (Lithuania).

The only, so called, high risk reactors (RBMK-Chernobyl type- or VVER 440-230 models), that have been shutdown since 1986 are:

Chernobyl unit 2, which suffered a fire in 1991, but according to plant officials will be restarted in 1996. 

Medzamor (Armenia) units 1 and 2: These were shutdown in 1989 due to local opposition, but unit 2 was restarted in October 1995 and it is reported that unit 1 will be restarted in 1997.

There are a number of bi-lateral aid agreements which bring the total assistance programme to about 1013.88 million ECU. However, the wisdom of attempting to retrofit the reactors has been questioned. In September 1992, the then director of Industry and Energy Department of the World Bank Anthony Churchill stated.

CONCLUSION

Despite massive international concern over nuclear safety in CEE and the fSU and hundreds of millions of dollars in grants and loans to the region, there has been little increase in safety and none of the "high risk" reactors have been permanently closed. The only conclusion that can be reached is that the money is going to the wrong programmes. Instead of investing in energy efficiency and alternatives, the majority of vital resources are being paid to western consultants and contractors to review nuclear safety.

The accident at Chernobyl has had a huge impact on the environment especially in Belarus, Russia and Ukraine. In addition, it has had a negative impact on the health of the hundreds of thousands of people involved in the clean-up and those who still live in heavily contaminated areas. Due to the long half life of many of the radio-nuclides released a huge area will remain contaminated for generations to come. International organisations, such as the IAEA and WHO continue to maintain that other than Thyroid cancers there are no negative physical health effects from Chernobyl. However, with the exception of Thyroid cancers no large scale international study has been completed which investigates health effects in high risk groups e.g. the Liquidators. Without adequate information it is impossible to draw firm conclusion.

Due to the serious risk of a second accident at Chernobyl it is essential that the station be closed immediately and because of the safety problems of the existing Sarcophagus it is necessary to take immediate action to secure it and begin preparation for the construction of a second structure. Both of these require urgent Western financial support to avoid another environment and ecological disaster.

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