1- Prelude: an accident waiting to happen

07/06/2016
Article

Chernobyl is safe…. Well, until April 26, 1986, that is…Before the Chernobyl accident very little was known about the Chernobyl type reactor, the RBMK. One of the few publi-cations before 1986, in the December 1983 issue of the Ger-man nuclear industry monthly atomwirtschaft was written by H. Born from one of the main German utilities VEW. He writes: "For operational safety, the nuclear power plants (VVER and RBMK) are equipped with three parallel safety systems. The power plants are designed to withstand natural disasters (hur-ricanes, floods, earthquakes, etc.) and to withstand aircraft crash and blasts from outside. The safety is increased by the possibility in Russia to select a site far away from bigger towns." (page 647: "Zur Betriebssicherheit sind die Kraftwer-ke (VVER and RBMK) mit drei parallel arbeitenden Sicherheit-systeme ausgeruested. Die Kraftwerke sing gegen Naturka-tastrophen (Orkane, Ueberschwemmungen, Erdbeben, etc) und gegen Flugzeugabsturz und Druckwellen von aussen ausgelegt. Die Sicherheit  wird noch durch die in Russland moegliche Standortauswahl, KKW in gewisser Entfernung van groesseren Ortschaften zu erstellen, erhoeht."

In the June 1983 issue of the IAEA-bulletin, Mr. B. Semenov, Deputy Director General, Head of IAEA Department of Nu-clear Energy and Safety, sums up "many factors favoring the channel-type graphite-uranium boiling-water reactors" and concludes: "The design feature of having more than 1000 individual primary circuits increasing the safety of the reac-tor system – a serious loss-of-coolant accident is practically impossible." (page 51).

1972 
In 1972 a discussion took place in Kiev about the type of nuclear plant to be built at Chernobyl. Chernobyl's director, Bryukhanov, supported construction of Pressurized Water Reactors (PWRs). He informed the Ukraine Minister of Energy, Aleksei Makukhin, that an RBMK (a boiling water reactor) releases forty times more radiation than a PWR. However, the scientist Alekzandrov opposed this, saying that the RBMK-1000 was not only the safest reactor, it produced the cheapest electricity as well. For this reason it was decided to build the RBMK pressure tube reactors. 

1979 
February-March: according to data in the possession of the KGB, design deviations and violations of construction and assembly technology are occurring at various places in the construction of the 2nd generating unit, and these could lead customary for all sections of public employment to have their own special day, when they receive public acclaim for their work and are given extra bonuses. 
That the production of electricity started on 20 December is quite remarkable, because usually there is a time lapse of about six months between the completion of the construction and the plant becoming operational. On this subject Zhores Medvedev noted that it was common practice in the Soviet Union for people to declare an industrial project to be ready for operation on the understanding that any problems will be solved as quickly as possible. In this way, the production plan already set can still be met. Besides which, not signing the declaration on 31 December 1983 would have resulted in thousands of employees missing their chances of bonu-ses and other extras. This concerns bonuses of up to three months salary extra. Later it became apparent that in the period up to 1985 the turbine had been tested, but without results. The question is still why the test was not repeated again immediately, but had to be left until April 1986.


Nuclear Europe, January 1984

1984 
In April 2003, secret KGB documents released in Ukraine show that there were problems with the Chernobyl nuclear plant. One 1984 document notes deficiencies in the third and fourth block, and also of poor quality of some equipment sent from Yugoslav companies. 

1985 
April: The Minister of Energy, Anatoly Mayorets, decreed that information on any adverse effects caused by the functioning of the energy industry on employees, inhabitants and environment, were not suitable for publication by newspapers, radio or television. On 18 July 1986, shortly after the Chernobyl accident, this same minister forbade his civil servants from telling the truth about Chernobyl to the media. 

1986
February: Vitali Sklyarov, Minister of Power and Electrification of Ukraine, in reference to the nuclear reactors in Ukraine, is quoted in Soviet Life magazine (page 8) as saying: “The odds of a meltdown are one in 10,000 years.” 
27 March: Literaturna Ukraina (Ukrainian Literature) publis-hes an article written by Ms Lyubov Kovalevska (believed to be a senior manager at Chernobyl NPP) in which she writes that substandard construction, workmanship and concrete, along with thefts and bureaucratic incompetence are creating a time bomb “The failures here will be repaid, repaid over the decades to come.” 
It remains uncertain whether the information on the course of the accident is completely reliable. In 1987, five pos-
sible courses of events leading up to the accident were put forward. However, the following account is the one generally accepted. 


The turbine test 
One of the tests incompletely carried out before the reactor becoming operational was on the functioning of the turbine in the case of a defect. 
That the production of electricity of the fourth Chernobyl reactor started on 20 December 1983 was, as said, quite remarkable, because usually there is a time lapse of about six months between the completion of the construction and the plant becoming operational. 
All the components have to be tested before the actual production process is started. But, in Unit 4 at Chernobyl there was a celebration in March 1984 (only three months after the reactor was operational) to mark the fact that already one million kilowatt hours had been produced, even though at that time not all the components had been thoroughly tested. 
One of the tests incompletely carried out before the reactor becoming operational was on the functioning of the turbine in the case of a defect. 
If a defect is present, the turbine should then slow down, but continue to produce electricity. This electricity is ne-cessary to work the circulation pump and control rods, and to provide lighting for the control room and control panel. This supply of electricity is essential for the safety of the reactor, and on no account should it fail. 
Because it takes twenty seconds for the control rods to reach their most extreme position in the case of a defect, it is of vital importance to know whether the turbine can pro-duce the necessary electricity for those twenty seconds, until the emergency generator is able to take over the sup-ply of electricity. This test was carried out on the night of 25 - 26 April 1986, and was the cause of the disaster. This test should have been carried out before the power plant was put into operation. In actual fact, such a test was carried out earlier - but failed. This became apparent in July and August 1987 during the trial of six people held to be responsible for Chernobyl. The judges' verdict states that on 31 December 1983, director Bryukhanov signed a document declaring that all the tests had been carried out successfully.

Times-zones
Local times: At the time of the 1986 accident, Ukraine was one of the Republics of the USSR (Union of Socia-list Soviet Republics) and had Moscow-time (GMT+3). Although Ukraine changed its time to GMT+2 after it declared independence from Moscow in August 1991, times mentioned in the Chronology are historical local times (GMT+3). Times mentioned concerning Sweden's Forsmark, are also GMT+3. Time difference (in 1986) between Chernobyl and Sweden was 2 hours.


25 April (Friday) 
13.05 hours (local time): Preparations for the turbine test begin. For this test, the plant's capacity must be reduced and for this reason one turbine is turned off. 
14.00 hours: The controller of the Ukraine electricity network requests that the test be delayed. All electricity from Unit 4 is necessary. It is not clear why it was not predictable before-hand that work would have to continue all through Friday afternoon in order to achieve the production planned for April.
16.00 hours: The day shift leaves. The members of this shift have been given information about the test during the pre-vious days, and know about the entire procedure. A special team of electronic engineers is present. 
23.10 hours: Preparations for the test start again. The ten hour delay has a large number of consequences. Firstly, the team of engineers is tired. Secondly, during the test, the eve-ning shift is replaced by the night shift. This shift has fewer experienced operators, besides which they were not prepared for the test. Achier Razachkov, - Yuri Tregub and A. Uskov are the operators who were responsible for carrying out the test earlier in the day: later in interviews they declared that test procedures were only explained to the day and evening shifts. Yuri Tregub decides to stay and help the night shift.

26 April (Saturday) 
01.00 hours: During preparations for the test, the operators have difficulty keeping the capacity of the nuclear plant sta-ble. While doing this they make six important mistakes. 

  1. The control rods which can stop the reactor are raised higher than regulations permit. Operator Uskov of the day shift said later that he would have done the same. He said: "We of-ten don't see the need to follow the instructions to the letter, because rules are often infringed all around us." As well as this, he pointed to the fact that during training it was repeated over and over again that "a nuclear power plant cannot ex-plode". Operator Kazachkov said: "We have often had fewer control rods than were required, and nothing ever happened. No explosion, everything just went on as normal." 
  2. The plant's capacity decreases to below the safe level. Because of this the core becomes unstable. Preparations for the test should have been stopped by now. It should have been obvious that all attention should be given to measures for regaining the plant's stability. 
  3. In order to raise the capacity, an extra circulation pump is turned on. Because of the strong cooling down, the pressure falls, thus reducing the reactor's capacity rather than increa-sing it. Normally at this stage the scram system should start working, but in order to still be able to carry out the test, this system is turned off. 
  4. The automatic emergency shut-down system is turned off in order to prevent the reactor stopping itself. 
  5. The systems to prevent the' water level decreasing too much and the temperature of the fuel elements becoming too high are also turned off. 
  6. Finally, the emergency cooling system is turned off to prevent it working during the test. 
    1.23.04 hours: The real test now begins. The power plant's capacity suddenly increases unexpectedly. 
    1.23.40 hours: Leonid Toptunov, responsible for the control rods, presses a special button for an emergency shutdown. The test has been going on for 36 seconds. 
    1.23.44 hours: The control rods start to descend, but shocks can be felt. The operators see that the control rods have be-come stuck. The fuel tubes have become deformed because of the large increase in the steam pressure. 
    1.24.00 hours: The test has now been going on for 56 seconds. Pressure in the reactor is now so high that the fuel elements burst and small particles land in the cooling water. The cooling water turns into steam and pressure in the tubes increases: they burst. 
    The 1000 ton lid above the fuel elements is lifted: the first explosion. The release of radiation starts. Air gets into the reactor. There is enough oxygen to start a graphite fire. The metal of the fuel tubes reacts to the water. This is a chemical reaction which produces hydrogen, and this hydrogen explo-des: the second explosion. Burning debris flies into the air and lands on the roof of Chernobyl Unit 3. (There was barely any attention paid to this hydrogen explosion in the Soviet report about the accident. In studies commissioned by the US government, however, it was concluded that the second explosion was of great significance, and that the original ex-planation of the accident was incorrect. Richard Wilson of the Harvard University in the US said this second explosion was a small nuclear explosion.) 
    The head of the night shift, Alexander Akinhov, and the engi-neer responsible for industrial management, Anatoly Diatlov, do not believe that an accident has taken place. When some-body claims the core has exploded, they send out operators to examine the core. These people are killed by radiation. On hearing the report that the reactor has been destroyed Aki-mov cries out, "The reactor is OK, we have no problems." Akimov and Diatlov, assisted by manager Bryukhanov and engineer N.Fomin, keep ordering the operators to add more cooling water. They remain convinced that there is nothing wrong. Akimov and Toptunov, who was responsible for the control rods, both died of radiation illness. Diatlov and Fomin were both sentenced to ten years imprisonment for infringe-ment of the safety regulations. However, at the end of 1990 they were both released. 
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