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Chernobyl Accident: Evolution of Sights

B. Gorbachev, J. Solomatin 25.04.2006

20 years have already passed since the time when two narrow tongues of flames one behind another each of the height from 100 to 500 m and the sharp sound similar to a shot from a gun have informed silent stars that in 4-th block ChAES the largest in the world nuclear accident took place. Disputes on its circumstances and causes proceed till now. Nevertheless every year with the appearance in the open press of a new trustworthy information researchers step by step come nearer to disclosing of its last secrets and true causes paying no attention to the attempts of the interested persons to disinform the Ukrainian and international public opinion.

 

Three Points of View Plus One More But Very Important

It is written a lot about the causes and circumstances of Chernobyl accident. Both scientifically reasonable and disputable and even fantastic, beginning from the nuclear bomb enclosed in a reactor and finishing extrasensory influence of aliens on the brains of people in the shift. Now there are over than 110 versions proposed by different authors. However only three of them are scientifically reasonable though not indisputable on a number of the basic moments.

The first one was brightly expressed in the well-known report on the Chernobyl accident presented to IAEA by the USSR in 1986. In this report one can precisely follow an idea according to which personnel on duty 6 times that night roughly broke the rules of safe operation of a reactor making thus the work of the reactor uncontrollable, switched off almost all means of emergency protection of the reactor, as a result the reactor went to dispersal and blew up. That meant that the reactor in general was good, the accident happened because of nonprofessional actions of the personnel.

In 1991 the commission formed by GosAtomNadzor connected the reasons of Chernobyl accident with presence on the ends of control rods long graphite water displacers. The last absorb neutrons worse than water therefore their simultaneous input in an active zone after pressing button AZ-5 having superseded water from channels SPS brought such additional positive reactance that the remained 6-8 "effective" rods could not compensate it any more. That meant that reactor producers who invented those displacers were guilty in the accident and not the personnel.

In 1992 special group of IAEA considered the materials on the Chernobyl accident presented to it at an official state level and agreed that movement of operating pivots in an active zone of a reactor could cause uncontrollable chain reaction in it. It looked like the consensus with the world nuclear public was found.

However this consent held on not for long for all three commissions could not answer a number of questions of principle convincingly. We shall bring here only three of them - the most basic ones.

The first C what made the personnel to actuate urgently emergency protection of a reactor of the maximum the 5th category (button AZ-5) in conditions when - according to all official versions C there were no emergency processes in a reactor? More than that - to press button AZ-5 two-three times.

The second - what are objective proofs that control rods really moved to an active zone of a reactor after pressing button AZ-5? We want to remind that till now no such proofs have been found. There are only subjective indications of witnesses which legally were responsible for safety of a reactor and to whom long prison terms if pivots "have not gone downwards" threatened.

The third - why supersensitive seismic stations fixed an explosion in ChAES at 1 o'clock 23 minutes 39 seconds and didnt fix an explosion of the reactor at the official moment of explosion at 1 hour 23 minutes 50-55 seconds though their sensitivity quite allowed them to fix it? Well, etc.

Years passed. Both sides remained at their own opinions. As a result strange position was formed when two solid official state commissions studied actually the same materials and came to opposite conclusions. It was felt that there was something wrong either in emergency materials or in the work of the commissions. The more that some of the important points obviously carried not evidentiary but declarative character. Besides at the close analysis of materials and commissions membership it became obvious that their forming strictly departmental affiliation of the chapters occurred. We want to remind that in the commission of the year 1986 the key tone was set by atomic scientists while in the commission of the year 1991 it was set by operators - natives from Department of Energy nomenclatures. Probably therefore both parties failed to prove the correctness to the other party. Researchers didnt get rid of their doubts completely.

For the sake of historical validity it is necessary to say that openly experts of RBMK-1000 reactor stated their doubts in accuracy of both official versions already in 1994: "the analyses have been executed till now are characterized by limitation of use of an available information. That circumstance that the primary information was inaccessible also contributed to such position. The data published had been prepared in haste and are incomplete ­, or selective and gradually oriented on the version predetermined.±

In translation from scientifically-diplomatic language it means that in 1994 atomic scientists clearly saw that materials of the official report of the USSR to IAEA in 1986 as well as official report of GPAN which followed in 1991 in no way could be treated as "truth in the last instance". The first one was prepared "in haste" and consequently the data in it "are incomplete" that is quite natural in those conditions. We shall remind that accident happened in the end of April, 1986 and preparation of scientifically and politically correct report about its causes as well as reconstruction of the process of the accident should had been finished till the end of June, 1986 C in 2-3 months. That proved to be very difficult because of the number of objective and subjective reasons. In particular also because of the fact that the investigation wasnt finished by the time.

The second report was prepared 5 years later in more favorable conditions when it was not necessary to hurry up and there was time for close studying of all circumstances of the accident. However the commission was headed by the native from Department of Energy nomenclatures. Probably therefore the main aim of work of this commission was not a search of an objective truth but something absolutely different. Atomic scientists noticed it at once for its materials obviously "were selective and gradually focused on the version set". In translation from the scientifically-diplomatic language that means that commission of the year 1991 applied maneuver which in science is called °adjustment of the facts under the certain concept". It is usually used by unfair scientific employees from careerist reasons or for creation to themselves of "exaggerated" authority.

The experience received by the author in discussions with people from the Department of Energy in connection with real chronology of Chernobyl accident generated conviction that they are not interested in objective truth. As a rule they are only interested in the opportunity to rescue honour of a departmental uniform being even in a hopeless situation. This purpose is for them the main motive power in "Chernobyl" discussions.

By the way, this general feature long before the accident was noticed by journalist L. Kovalevskaja: "Friends, acquaintances ... If one is criticized - everybody rushes at once to protect him not understanding even the essence".

In the same manner they, as a rule, conduct themselves in "Chernobyl" discussions. But such behaviour is not constructive for authors are convinced that to restore all process of the accident in details will be possible only in teamwork of atomic scientists and operators and not in confrontation. For the first better know the physical processes which pass in a Chernobyl reactor and can quantitatively estimate the role of each of them in any conditions while the operators better know the real side of work on blocks of the atomic power station which doesnt always corresponds to official that one for a show. Chernobyl accident one more time persuaded us in it.

After 1991 in the Ukraine two "independent" official attempts to understand the causes and circumstances of Chernobyl accident were undertaken. One of them took place in 1996 and the second in 2001. However, in essence, they were not "independent" and were derivative of materials of the commission of the year 1991. They didnt find anything unexpected for both these attempts were also headed by the natives from Department of Energy nomenclatures. While in materials of the commission 1996 still were certain objectively useful for researches information, particularly about the work of reactor coolant pump and about differences that were not principle in normative documentation which were in work in the year 1986 in the 4th block, an attempt of the year 2001 ended in °deflate±. In general both attempts disappointed the researches because objectively they didnt differ much from the materials and conclusions of the committee in 1991. That is naturally °raven do not pick ravens eyes±.

Independent acknowledgement of these conclusions was unexpectedly received in not so long ago unclassified materials of "competent bodies", devoted to Chernobyl accident. We shall quote here only two citations of them for it will be enough to understand:

" ­ the facts testify superficial carrying out of administrative investigation of the causes of occurrence of emergencies in ChAES ". ( Document 91 from the 19th of August, 1987)

" ­ the facts of poor-quality investigation by the departmental commissions of some emergency breaks in the Rovno, Zaporozhye and South-Ukrainian atomic power station are also revealed. The reason of such state of things is the subjective approach of the specified commissions protecting departmental interests". (Document 88 from the 16th of July, 1987)

Well, Department of Energy of the sample of 1986! I always recognize you by nonprofessional style in nuclear work and in personnel policy. Even if you will hide yourself under other name.

In 2001 the third, real version of circumstances and the causes of Chernobyl accident appeared. It was worked out using much wider and authentic documentary base than was at the disposal of authors of versions of 1986 and 1991 and by the organization which did not have a sharp necessity to rescue honour of a departmental uniform. According to this version, i.e., at a level of scientific up-to-day knowledge, real process of Chernobyl accident in a short summary can be represented like this.

Nonprofessional actions of the personnel (they are considered more detailed below) resulted in making a reactor uncontrollable. Further, most likely, overindulged by carrying out of promising electrotechnical tests at first personnel "had looked over" the beginning of uncontrollable chain reaction and then "was late" with manual input of protection. This "delay" allowed the reactor to pass to instant neutrons with the subsequent most powerful explosion. "Fixed" (theoretically) emergency automatics didnt work as it had been earlier disconnected by the personnel in the roughest infringement of the rules. For item 11.1.8 of the last unambiguously demanded from the personnel: "It is forbidden In any case to interfere with work of protection, automatics and blocking except for cases of their malfunction ­ ". One cant say more clearly.

But how is it possible to disconnect "fixed" automatic protection of a reactor? It appears to be possible if to take advantage, to expressed it softly, ­"off-nominal means". This major circumstance earlier was persistently ignored by the Department of Energy nomenclature and was announced by the °Nuclear Minister± of the Russian Federation A.J.Rumjantsev in the official interview three years ago:

°The work of the safety protection interfered with the process of making it (reactor) high-powered. Then the personnel blocked its work by wedging out some of the buttons and sealing the other with the adhesive tape±.

Well, well, well! Such, let us say, criminal handling with reactor cant be imagined by its creators.

These conclusions were also confirmed by the results of independent investigation led by "competent bodies". Their investigatory group under direction of the vice-president of KGB of the Ukraine - general J.V.Petrov C had already started to work in ChAES at 5 o'clock in the morning on the 26th of April, 1986. In two weeks it came to final conclusions. For brevity we quote only two citations from these unique documents, everything will become clear to unbiased reader:

"­ the general reason of the accident was low culture of workers of the atomic power station. It is a question not of qualification, but of culture of work, internal discipline and feeling of the responsibility" (document 29 from the 7th of May, 1986).

" Explosion has occurred owing to some rough infringements of exploitation rules, technology and non-observance of regulations of safety in work of a reactor of the 4-th block of the atomic power station" (document 31 from the 11th of May, 1986).

They didnt refer any more to this question. Someone can be surprised at the fact that "competent bodies" revealed the true reasons of Chernobyl accident in two weeks. It is natural because unlike the official commissions their investigation relied on much more authentic documentary base. It is discussed in details below. The events had begun with electrotechnical tests in the 4-th block of ChAES, the tests which didnt represent any nuclear danger at all.

Electrotechnical Tests in the 4th Block of ChAES

After almost triennial operation the 4-th block should be stopped for average scheduled repair. Before a final stop the personnel on duty had to lead tests of the new device in the steering equipment in one of possible emergencies - sudden switching-off of submission of the electric power from an external network which feeds this equipment.

On the modern atomic power stations for such emergency case automatic transition to power supplies from regular diesel engine-generators is stipulated. But so that they have time to gather working turns 40-60 seconds are necessary. To provide with power supplies the equipment of safety system in this critical time interval old reactors contained the huge storage batteries which occupied the whole halls and were expensive in exploitation. Later an idea to use for these purposes heavy steam turbo-generators (TG) appeared, these generators rotating mechanically after switching-off of an external network could develop by means of the new device the electric power sufficient for a feed of the steering equipment until diesel engine-generators will not enter into an operating conditions. Then it will become possible in new blocks of the atomic power station to refuse from the storage of batteries that will reduce the price of block construction and also will reduce the price of the electric power after input of the block in operation. As you can see, an overall objective of these works was quite reasonable.

The next advanced updating of such device should be tested in the 4-th block at the night from the 25th to the 26th of April, 1986. Similar tests had been already tried out in other blocks of ChAES with the previous updatings. All of them had ended without positive result, but there was a strong hope in final success. Thus the personnel of ChAES had experience of carrying out of such tests.

However, experts unanimously tell that such tests would be professional to carry out in the factories which produce turbines for atomic power stations but not on the territory of the working reactor.

 

Mistakes of the Personnel

However at drawing up of the tests program and also during their preparation and carrying out a lot of rough infringements of rules of safe operation of a reactor was admitted. Skilled operators counted 7 of them. In "independent" Ukrainian mass-media they were not illuminated in all set. Therefore it is sensible to list them briefly:

"C intending to leave "iodic hole" an operative stock of reactance was lowered below admissible size thus having made emergency protection of a reactor inefficient;

- LAR system was disconnected mistakenly that led to a failure of reactor capacity below stipulated by the program; the reactor appeared to be in a unhandy condition;

- all eight main circulators were connected to the reactor with emergency excess of consumption of some of them that made increased coolant temperature close to saturation temperature (program conditions);;

- intending if necessary to repeat experiment with de-energizing they blocked protection of a reactor on a signal of a stop of the device at switching-off of two turbines;

- protections at water level and steam pressure in separator drum were blocked aiming to carry out tests notwithstanding unstable work of the reactor. Thus protection at thermal parameters was disconnected;

- systems of protection against the maximal design accident were disconnected proposing to avoid false actuating of the emergency system at carrying out of tests loosing an opportunity to lower scales of probable accident;

- personnel blocked both emergency diesel engine-generators as well as working and launching-reserve transformers having disconnected the block from sources of emergency power supplies and from a power supply system, intending to lead "pure experience" and actually having finished a circuit of preconditions for limiting nuclear catastrophe..."

Here you are only officially registered infringements. Each of them can be discussed a lot and for long. We shant also analyze other ones which were officially registered too. In particular, the absence of the obligatory coordination of the program of tests with the Supervisor, the Chief Designer, the General Design Engineer and the State Atomic Energy Inspection as well as receptions from them the official sanction for carrying out of such tests that had been stipulated in official documents at the process of transfer of APS to the Department of Energy. To justify it one can make usage of the fact of absence of the answer to the official reference of ChAES management from these higher instances. Though it wasnt officially allowed, but it wasnt forbidden officially. As in the saying: if it is impossible but very desirable than it is possible. In the case it was desirable, apparently, very strongly.

 

Accident

The 26th of April, 1986. Chernobyl Atomic Power Station. Four power units of 1000mW each. Reactors of type RBKM-1000. They are the result of original domestic development of frameless water-cooled boiling reactor of channel type. In comparison with frame reactors they have advantages - economic, operational, etc. But as the English saying says "any advantage has its lacks". And the reactors of type RBKM-1000 had such "lack" as consequence of its advantages. Its safety exploitation required strict following of regulations i.e. safety exploitation rules for the reactor itself can suffer °unceremonious treatment± only to the definite extend.

At the level of present-day scientific knowledge its natural development process looked like this:

At 00 o'clock 28 minutes on 26.04.86 the personnel of the 4th block ChAES beginning electrotechnical tests made a mistake at switching of steering from system of local automatic control (LAR) to system of automatic control of capacity of the basic range (§R). Due to this mistake thermal capacity of a reactor fell below 30mW, neutron capacity fell up to zero and remained thus within 5 minutes. The process of a self-poisoning by short-living fission products automatically started in the reactor. In the whole world at reaching such situation the reactor should be simply shut down till the moment when the reactor reestablishes its capacity. After that it is actuated once again. This practice is a common one, there shouldnt be any difficulty for the experienced personnel of the 4th block.

The only thing is that this process is very bothersome and takes quite long time on the reactor of the APS. In our case it also strips off the fulfillment of the electrotechnical tests program with all ensuing troubles for the personnel C administrative and financial. That is why intending °to finish testing as soon as possible±, as the personnel explained later, they began to derive control rods gradually from the active zone of the reactor. Those actions should help the personnel to raise the capacity and to continue the fulfillment of the testing.

Similar situation had been stipulated by the rules in which it was written: "Raise of capacity of the block after a short-term stop is made after elimination of the causes of capacity decrease under written instruction of CSS (the chief of the station shift) in the "Register of Process Conducting" and of CEMR (the chief engineer of management of a reactor) in operative magazine". However the personnel ignored this requirement of the rules.

After the raise of the capacity up to 200mW the personnel switched on system of automatic control of capacity §C and helped it manually to level distribution of energy liberation on an active zone of the reactor. Joint actions of AC system and manual management resulted in continuation of outputting of the control rods from an active zone. It should compensate a proceeding decrease in capacity of a reactor which was the consequence of self-poisoning processes. This procedure on reactors of the atomic power station is also usual and can be the cause of the nuclear threat only in the case when the number of the rods will be not enough for the present state of the reactor.

However the conclusion of control rods naturally was accompanied by the reduction of size of an operative stock of reactance (§°SR) which defines ability of a control system to operate the reactor safely. In relation to §°SR the rules quite definitely demanded: "Work of the reactor with less than 26 rods is allowed by the sanction of the Chief Engineer of the station". However this rule was also ignored.

Further the rules quite definitely stated: "At the decrease of an operative stock of reactance up to 15 rods the reactor should be immediately shut down". Therefore, when in the process of a conclusion of control rods from active zone OSR was decreased up to 15, the personnel should muffle the reactor. We want to repeat that that was the direct requirement of the regulations and the direct official duty of the personnel. But it was again ignored.

By the way, the first time such infringement in the 4-th block happened at 7 o'clock 10 minutes on the 25th of April, 1986, i.e. almost one day prior to the accident and proceeded approximately till 14 o'clock. Why the reactor had not blown up at this time still remains among the unsolved riddles of Chernobyl accident. It is interesting to note that during that time the change of the operative personnel shift was fulfilled, the Chiefs of the shifts of the 4th block changed, Chiefs of shifts of the station and other station heads and strange as it may seem nobody gave the alarm as if everything was in its norm though the reactor at this very time already was on the border-line of the blowing. Automatically the conclusion naturally suggests itself that infringements of such type, apparently, were the usual phenomenon on ChAES. This conclusion is confirmed also by the evidence of I.I.Kazachkov who was the chief of the day shift in the 4th block worked on the 25th of April, 1986: "I shall say that it was not the first time when the quantity of the control rods was below the admissible one - and nothing ever happened ­", "­ nobody from us imagined that it is fraught with nuclear accident. We knew that its forbidden to do like that but did not think ­ "

For the second time it happened already on the 26th of April, 1986 soon after midnight. But the personnel did not begin to shut down the reactor that time also and continued to deduce rods for maintenance of the reactor capacity. As a result at 1 o'clock 22 minutes 30 seconds §°SR decreased up to 6-8 rods. This fact also didnt stop people who started the electrotechnical tests. Thus it is possible to assume confidently that the personnel continued conclusion of rods till the moment of explosion for by some estimations to the moment of explosion the number of OSR was decreased up to 0.

Nobody all over the world works like this for there are no means of safe control over the work of the reactor which is in process a self-poisoning. The staff of the 4th block didnt have them too. Therefore the further conclusion of control rods after §°SR became less than 15 rods could be carried out only on the basis of intuition. From the professional point of view it was an adventure in its pure kind. Why did they embark on it? It is a separate question.

At any moment after 1 hour 22 minutes 04 seconds the intuition of the personnel, apparently, failed and from an active zone of a reactor the superfluous quantity of rods was deduced. As a result the condition of the reactor became uncontrollable. It is possible to list tens of various processes which are usually passing in the reactor which in such conditions could provoke its dispersal. It is possible to specify among them such processes which did not depend at all on a will of the personnel. For example, great enough fluctuation of neutron fields or density of heat-carrier in one of the parts of the reactor active zone. It should be said that at the reactors normal work all these dangerous processes are suppressed by its steering system by means of input of control rods, i.e. negative reactance to the reactors active zone with a speed of 1 Msec at working OSR = 30 for the reactor RBMK-1000.

Which of these processes caused uncontrollable growth of capacity of the reactor hasnt been found out till now. Nevertheless in works belonging to the Institute of Safety Problems of APS of the National Academy of Sciences of the Ukraine quantitatively shown that version which was popular at first about the processes of input of superfluous positive reactance due to presence of graphite displacers on the ends of control rods at their prospective movement in an active zone of a reactor after pressing button AZ-5 and also "replacement" of neutron fields in the bottom part of an active zone in conditions of Chernobyl accident basically could not provoke uncontrollable growth of capacity of the reactor of the 4th block. It is possible to tell for sure only that the reactor had begun dispersal on late neutrons and in 20 seconds continued it on instant neutrons already. The means of management of the reactors in such condition hasnt been created yet and hardly will be created at all. Therefore during the 100-th shares of second a thermal emission in the reactor increased up to 2500-3000 degrees and then the process which is called thermal explosion of the reactor began.

Exteriorly it was quite impressive scene. Here you are as it looked like from afar from the side of water-cooling pond of ChAES on which bank resting workers of the station were fishing:

"I saw well a flame above the block 4 which by its form was similar to a flame of a candle or a torch. It was very dark, dark-violet with all colors of a rainbow. The height of the flame was up to a cut of a pipe of the block 4. It looked as if it went back and the second clap similar to the busted bubble of a geyser was heard. In 15-20 seconds another torch appeared, it was narrower than the first, but 5-6 times higher. The flame slowly grew and then disappeared as in the first case. The sound was similar to a shot from a gun. Resonant and sharp. We went.±

And here is how it looked from the nearby. L.Butrimenko - former security guard of the ChAES told it in details. His post was in 100 meters from the 4th block thus he was the only person who saw the accident at such a short distance: "At half past one I heard the first explosion. It was resonant as if a tram banged, but very strong. There was a shake as at earthquake. I turned to a reactor. The second explosion happened before my eyes. I had time to notice how the broken off roof was raised. Pieces of concrete, stones flew apart but I had time to hide myself from fragments. Explosion was of such force that concrete plates weighted one and more tons rejected from the reactor to a distance of fifty meters. Some of them fell out of a fence and a control strip".

Its exterior consequences are very well seen on photos made in May, 1986.

That was the beginning of Chernobyl accident. Its direct reason was the thermal explosion of the reactor similar to explosion of a steam boiler C the reason why it is sometimes called steam. We want to emphasize that it was thermal explosion not nuclear one. Nuclear reactors cant blow up as a nuclear bomb for the speed of development of uncontrollable chain reaction in them in millions times is less than in a nuclear bomb. This is the reason why no fire balls "brighter than thousands of suns", no all-destroying air-blast appear at the thermal explosion of the reactor. In 15-20 seconds it was followed by real explosion of hydrogen-air mixture which had pure chemical nature. Its consequences made Chernobyl °famous± all over the world.

 

Causes of Mistake

The main source of errors in conclusions of the official commissions and many informal researchers can be named as noncritical attitude to the published official and informal documents or their copies on Chernobyl accident.

For example, all official versions of accident passing after 1 hour 23 minutes 43 seconds are based on data of the printout of DREG which is considered as the document adequately registered sequence of emergency events and the time when they occurred­ But it is obviously not so as the time specified on this printout is not the time of the event but the time of recording of the information about the event into the magnetic buffer. The event itself took place earlier. That is the peculiarities of work of this registrar. Shift in time between the event and its registration on the printout appears because of the 2-seconds cycle needed to examine indications of all the devices and also because of the lowest C the 7th C priority of such records.

According to R&D Institute of Power Energy this shift can last minimum 2 seconds, maximum 4 seconds at normal work of a reactor, at an emergency it can last more. Here again is important to note that even if to accept the duration of this shift as 2 seconds than all official and informal versions of Chernobyl accident automatically become erroneous. Such major circumstance was concealed from the publicity for years.

But if this circumstance from the very beginning was well-known to experts on the reactor of the 4-th block than how can we explain their mistakes? The answer to this rather and rather painful for vanity of many researchers question is contained, according to the authors of this article, in materials of the former inspector of the General Prosecutor Office of the Ukraine - S.Yankovsky: "I was a participant of this investigation from the first hours after the accident up to a sending of criminal case to court. This unique in its documentary content criminal case consists of 57 volumes of investigatory documents and numerous appendixes hitherto laying as a dead weight in archive of the Supreme court of Russia. Many of appendixes till now "hit the eye" but comprise terrible information of evidentiary force. I am sure that the majority of documentary data havent heard of in the Ukraine. The case was absolutely confidential, we had withdrawn primary documents immediately and by the evening of the 28th of April, 1986 they were already in Moscow. The materials that numerous experts studied after that were basically cut down copies or falsification in general ".

One cant say more clearly than it was said in the last phrase. It is easy to understand the reason of mistake of our outstanding atomic scientists. In fact they could not imagine that someone will fob off them for studying not originals of emergency documents but their cut down copies and even falsification.

 

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