An instant decision. Have you often experienced such situations in your life? Fatal risk or an adequate solution within the current situation? Having pressed a second before the irreversible catastrophe “Emergency protection of the 5th level, AZ-5”, the Chernobyl operator Leonid Toptunov actually launched an emergency brake. It was supposed to stop the reactor, regardless of conditions or circumstances. Emergency protection is therefore called “emergency”. It does not depend on erroneous actions, nor on incorrect decisions, nor on breakdowns, nor on malfunctions on the unit, nor on the operator’s qualifications, tsunami, storm, earthquake, or even the end of the world!
Launching the AZ-5, Leonid Toptunov was convinced that the protection would prevent the tragedy. But the irreparable happened. He could not only prevent a disaster at the Chernobyl nuclear power plant, but also avoid his own death from large doses of ionizing radiation. Pressing the AZ-5 has become a fatality. Beside this, according to experts, an accident at that time was already inevitable. Toptunov had every right to take advantage of emergency protection in the current conditions. Moreover, he was obliged to do so. However, due to flaws in the design of the reactor, emergency protection did not stop the reactor, but dispersed it, up to a catastrophic explosion. The AZ-5 worked “the other way around”. That is what happened.
The improper operation of the reactor emergency stop system can be compared with the situation when the driver behind the wheel presses the brake, but it turns out that due to defects in the design of the car. Pressing the brake in some cases gives a spark to the gas tank! Obviously, this inevitably leads to a vehicle explosion! There are many disputes around the causes of the Chernobyl accident, even after 34 years from the time of the disaster. There is no longer either that “mighty Soviet country” or the omnipresent KGB that guarded it, but secrets regarding the Chernobyl events, as you know, still exist.
Whose conclusions should be trusted?
Today, the conclusions of nuclear physicists and designers are basically the same. Both agree that there were two root causes of the disaster:
- improper operation of the AZ-5, “the final effect of reactivity”;
- positive steam reactivity effect.
In general, the most terrifying thing is the fact that the reactor design revealed. Just think about it: more than thirty violations of safety rules. And such, to put it mildly, “imperfect type of reactor” functioned in the vast majority of nuclear power plants of the former Soviet Union. But, when it comes to the culprits, the opinions of experts differ. Designers believe that it was the operators who, after making a number of errors, brought the reactor to a state where its design flaws, as they say, “got pretty gnarly”. And the operators are convinced that they received the reactor without brakes from the designers. And what disturbs them the most is that the reactor’s flaw was carefully hidden from the operators.
The professional differences between designers, operators and their followers do not subside. After more than three decades after the accident, they still find out which of them is to blame. However, to some extent, these disputes can be justified only taking into account the Soviet realities, when the issues of responsibility in the nuclear industry were not resolved by law. Today, Ukraine, like other nuclear-weapon countries with developed nuclear legislation, blames the companies that operate the reactor as the culprit for nuclear incidents that caused damage to the population.
It is the operating company that is completely responsible for the safe operation of the reactors and for compensation for losses caused. It was this company that chose the type of reactor, perhaps not the most reliable. In addition, it chose the design of the nuclear power plant, its location, chose the manufacturers of equipment, transport companies, construction contractors, installers, repairmen and the like. Such a norm exists in the world. This was done in order to prevent the “dispersion” of responsibility between all organizations involved in the design, construction and operation of a nuclear power plant.
Chernobyl operators are guilty without guilt
Regarding the actions of the operators in 1986, experts assure that their actions were not absolutely flawless. However, the violations committed by the operators, according to many serious experts, have the same relation to the explosion of a reactor as the lack of a first-aid kit in a car before the gas tank exploded in the above comparison. That is, essentially no.
Researchers at the causes of the Chernobyl accident note that operators have not complied with the requirement to comply with the permitted value of one of the reactor parameters, which is called the “operational reactivity margin”. This is hard to believe. The operators did not have a device for measuring this parameter! Exactly so: there was a requirement in the instruction, but there was no measuring device. Such a device was installed at the Chernobyl reactors only after the accident, as well as at all other identical reactors operated at nuclear power plants of the former USSR.
Before the accident, operators could order the calculation of this parameter on a computer, the results of which they received only after 20 minutes, which did not meet the requirements of operational monitoring of the state of the reactor. Moreover, the calculation was not accurate, since the computer program did not take into account all indicators of the current state of the reactor, and, as a result, the calculated value of the operational reactivity charge was always less than the actual value of this parameter.
There was no alarm before the accident that could alert operators of an unacceptable deviation of this parameter, and there was no automatic protection that would stop the reactor itself, as happens during a dangerous change in other important reactor parameters. Unfortunately, the designers did not plan any technical means of protection against such an accident, and only “verbally explained” their reservations to the operators. However, relying on purely organizational measures to ensure reactor safety without the use of technical or engineering means is a crime.
This approach is contrary to the design standards in the nuclear industry, which are used around the world.
In addition, the interpretation of the meaning of “operational reactivity margin” and its importance before and after the accident was completely different. Only after the accident in 1986, the designers began to prepare about the possibility of a reactor explosion if this parameter was reduced, although before the accident there was no talk of this. Then, they talked only about possible complications in controlling the reactor.
In other words, the designers did not only consider it necessary to install a device to control this parameter, but they also actually misled the operators regarding the importance of this indicator. The reason is the inappropriate secrecy that prevailed in Soviet times, due to which the flaws in the design of the reactor were kept secret even from the operators who controlled these reactors.
Strange as it may seem, the new flaws of the Chernobyl reactors, which appeared as a result of … improvement of the reactors after the disaster, were also subsequently classified.
Did you eliminate design flaws? The information was hidden …
The fact is that in 1986 reactors like Chernobyl were shut down to eliminate, where possible, all design flaws. A lot of serious work was done, thanks to which, in particular, the emergency shutdown rate of the reactor was significantly increased, the control algorithm was improved, the design of the reactor controls — rods was changed. The “filling” of the reactor itself was fundamentally changed, and so on.
A few months later, when the modernized reactors resumed operation, scientists, designers, and energy officials carefully studied what happened as a result: what did the modernization of the reactors do? In June 1987, the research results again acquired the signature stamp.
Only after the lapse of time, it became possible to find out what was written in that secret document. It turned out that the primary cause of the accident at the fourth reactor of the Chernobyl nuclear power plant was “the possibility of a local occurrence of an uncontrolled self-sustaining chain reaction”.
The main reason why such a catastrophic situation may become a reality is indicated by insufficient accuracy, sensitivity to inadequate control capabilities. Simply put, the reactor could become naughty, accelerate by itself. At the same time, there were simply no opportunities to curb such an uncontrollable state that operators could take advantage of. Honestly and frankly!
The authors of the report also openly wrote that after modernization, the Chernobyl reactors, as before, can sometimes become uncontrollable. And for some parameters, as indicated in the report, the reactors became even worse than they were before the upgrade! For example, situations are possible when in one part of the reactor the chain reaction intensifies, and in the other at the same time it decreases. That is, instead of one reactor, two separate ones actually form, which incredibly complicates the control of processes in the reactor and creates the danger of its transition to an uncontrolled state.
The document concluded: “it cannot be argued that the nuclear safety of the reactor today is ensured in all cases.” In other words, it cannot be guaranteed that the reactor will always be obedient. And what has the power done? Reactors were not stopped to eliminate new shortcomings, and the document was simply classified. And this is a year after the Chernobyl tragedy!