Chernobyl Nuclear Disaster (1986)

On the 26^th of April, 1986, at 1:23:45 am local time, a severe nuclear accident took place at the Chernobyl nuclear power plant, located in close proximity to the populated city of Prypiat in the Ukrainian Soviet Socialistic Republic (currently Ukraine).

As described by World Nuclear Association (2009), a shutdown of the 4^th Unit of the Chernobyl nuclear power plant was scheduled for a routine maintenance on the 25^th of April, 1986. The shutdown would also allow testing if the cooling of the core would still be supported by the slowing turbine in case of a loss of power. To enable the shutdown, the emergency core cooling system (ECCS) was switched off. The shutdown of the reactor was taking place as planned up until the moment when it was interrupted due to the demand for the power in the grid; at 11 pm the shutdown process was recommenced. According to the plan, stabilization of reactor had to take place at the power level of 700-1000 MWt, however as of 00:28 am, April 26, it fell to 30 MWt. By 1:03 am it was stabilized at 200 MWt level and it was decided to perform the planned test at that level. What the employees of that shift did not know is that already by 1:00 am the minimum operating reactivity margin (ORM) for the reactor of that type (RBMK) was already severely violated. By 1:22:30 am the ORM comprised eight manual control rods while the minimum permitted ORM was 15. The test was started at 1:23:04 am and a disaster was a matter of seconds. Under less than a minute from the moment the test was commenced, the power reached 530 MWt at 1:23:43 and kept rising. The steam triggered by rupture of the fuel elements acted as a catalyst for the explosion, whereas the positive void coefficient increased, the pressure in the reactor rocketed, the reactor support plate was detached and the rods got stuck before they even reached the reactor core. Finally, the reactor cooling circuit depressurisation took place due to the breakage of the channel pipes and triggered the consequent mass steam generation. This lead to the first explosion at 1:23:45 am (World Nuclear Association, 2009) whereas the sarcophagus around the reactor collapsed, water poured in and reacted with zirconium. The result of this reaction was hydrogen which caused the second explosion just several seconds later and prolonged graphite burning, while the destroyed core of the reactor was exposed to the atmosphere.

The Chernobyl nuclear accident was followed by long debates regarding what was the cause of the explosion and who was to be held responsible. While this is presented in more detail in the subsequent sections of this paper, the historical background of the USSR energy and

power sector should be briefly assessed now as it well contributes to the understanding of the path to that accident.

In the beginning of the 20^th century, the electricity production in Russian Empire comprised 1.9 TWh per year, which was a very low level for a country of that size. In fact, in terms of electricity production Russian Empire was lagging well behind even Switzerland, which was 500 times smaller in area (Kuznetsov, 1964). After the revolution of 1917 the Communist Party came to power, they developed a new vision for a new country – the Soviet Union. The Communist Party switched to the planned economy and put electrification among the top-urgent priorities and in 1920 the All-Russian Central Executive Committee of the Soviet Union announced establishment of a Sate Electrification Commission (GOELRO) which would work on creation of an Electrification Plan for the country (Lenin, 1964). Both the Commission and the Plan were under direct supervision of V. I. Lenin who deeply believed that electrification is a critical process to the successful transformation and industrialization of ex-Russian Empire. A 500-hundred page Plan was presented soon by GOELRO and massive construction works of a network of regional power plants and transmission and distribution systems commenced, and with the well-known Soviet 5-year plans the targets were heavily over-fulfilled (Geldern, 2012). Even the WW II could not stop the Soviet Union’s pursuit of electrification and by 1956 the Soviet Union was the 2^nd largest electricity producer after the USA with its total electricity output reaching 192 TWh in that year which shows more than a 100 times increase over roughly 50 years (Kuznetsov, 1964).

However, in early 1950’s it became clear that the electricity capacity was not yet sufficient for achieving all goals set by the Communist Party. Therefore, it was decided to expand into Siberia and the Far East as well as to have a closer look at the nuclear power potential (Lomakin, 2012). Worth mentioning, by that time nuclear power had already been a well-established scientific field in the USSR, however, it was considered for the military purposes only – bombs and fuel for submarines, and did not have any ready-available applications for the electricity generation. Hence, civil nuclear industry had to be developed from scratch which required huge investments into capital, knowledge and human capacity.

According to V. Legasov, who was the First Deputy Director of the Kurchatov Institute of Atomic Energy at the time of the Chernobyl accident and was appointed the Chief of the Investigation Committee of the accident, in terms of nuclear science, the Soviet Union was lagging behind the rest of the world for 10 years, so a big “catching up” challenge was awaiting (Lomakin, 2012). An extensive research and development program was initiated by

the State Committee for the Utilization of Atomic Energy to assess viability of different nuclear reactors and to conclude which reactors would be most suitable for the USSR (Semenov, 1983). Various types of reactors were considered, e.g. PWR, BWR, GCR. The research showed, however, that a uranium-graphite channel-type reactor cooled with boiling water, also known as the “Soviet design reactor” or RBMK, is the most economically appealing one. The first nuclear power plant based on this type of reactor was commissioned in 1954, in Obninsk, nearby Moscow, and in next 15 years similar nuclear power plants comprised roughly half of the total Soviet nuclear capacity (Zheludev, 1980). Worth mentioning, the USSR was particularly interested in developing fast breed reactors since such reactors were critical for realization of a large-scale nuclear programme. After almost a decade of experimenting and testing different technologies, in the second half of 1960’s it was finally decided that the VVER and the already discussed RBMK will be cornerstone of the long-term nuclear programme (Semenov, 1983).

It is critical to understand the nature of the Soviet Union as a country at the time it was stepping into the civil nuclear power era. It was a country which has just gone through a massive electrification process under enormous time pressure. What other countries were doing for a century, the Soviet Union accomplished under less than 30 years. The Communist Party had the ultimate power and through its subordinates was making orders which nobody would dare to question – the hierarchy was indeed strong and strict. Abundant number of commissions, councils, reporting groups and others was created to control and monitor every industry, including nuclear power sector, however they lacked clear vision, did not communicate with each other and were not properly structured, which altogether lead to over-bureaucratization and inefficiency (Dyatlov, 2005). Worth mentioning, the working style of controlling and monitoring bodies was skewed towards punishing for what has been done wrongly, rather than incentivizing and preventing wrongdoing (Lomakin, 2012).

Furthermore, the Soviet Union was an isolated country which put an explicit boundary between itself and the rest of the world with the famous “iron curtain”. While only people living in the Soviet Union knew how the country is like from the inside, the whole outside world could only see what the Soviet “public relation” offices would show them. The Soviets’ pursuits for self-sufficiency and strong unwillingness of being dependant in any respect on other countries, made it “reinvent the bicycle” many times – nothing could be borrowed from the West, not even a nuclear reactor design – this was developed in-house (Lomakin, 2012). Such policy had an important negative externality: the country was lacking

funds and adequate labour force, so it had to urgently establish universities and educate necessary specialists locally while being restricted with a limited budget. This yet again put efficiency of the whole nuclear industry into question.

To sum up, the 26^th of April 1986 witnessed a dreadful accident taking place in a country whose nuclear power sector was comprising 20 per cent of the whole electricity generating capacity throughout 1976-1980 (Zheludev, 1980), yet which had been developed in a rush and independently of what the whole scientific world had to offer, amid scarcity of available technologies, financial resources and adequate specialists. This should be kept in mind while evaluating probability and costs of the Chernobyl nuclear accident which is presented in the subsequent parts of this paper.