Chernobyl Through the Mist of Decades

Courtesy SSE ChNPP.

Courtesy SSE ChNPP.

By Will Davis

In the administration building of the Chernobyl nuclear power plant, a number of stained glass windows (as seen to the right) recall the optimistic tone of industrial Soviet-era art that can still be viewed today at power plants around the former USSR. That these are well preserved is not the result of a specific effort, but instead because of the essential abandonment of large parts of the facility, and even the entire region, after the most serious nuclear reactor accident in 1986 in history.


The particular type of nuclear power plant constructed at Chernobyl is so key to the accident that occurred that no account of the event can be written without full detail of the plant itself. The particular type, known in Soviet era terms as the “RBMK-1000,” was a large “pile” reactor (using, literally, a pile of graphite bricks to slow neutrons to the speed and energy to fission uranium-235), which incorporated thousands of fuel and coolant channels. The water passing through the core was boiled by the nuclear heat and passed to steam drums where any entrained water was removed. The steam then went to drive two identical turbine generators (to provide power to the grid).

Chernobyl NPP.  Unit 1 is nearest the camera; the ill-fated Unit 4 furthest.

Chernobyl nuclear power plant. Unit 1 is nearest the camera; the ill-fated Unit 4 furthest (Courtesy SSE ChNPP)

The Chernobyl complex, in what is now the independent Ukraine, was built over a long enough period that its four nuclear units (each “unit” is a combination of one reactor and two turbine generators) were of different designs, even though built side by side. The first two units were the earliest design, while Units 3 and 4 were of the second generation of RBMK-1000, which were intended to have an improved confinement for the reactor in case of accident. Even so, the structure was intended to contain only the rupture of two of the tubes in the reactor—which actually had about 1600 tubes.

The reactor core used in this type of plant was physically so large (a cylinder 21 feet tall and 36 feet wide) that power could be increasing rapidly in one part of the core (either “radially” or on one side, or else “axially” meaning at the top or bottom) while decreasing in another. This loose coupling of the core, combined with serious deficiencies in the control rods used to control and shut down the core, also played an important role in the accident that was to occur.

RBMK from INSAG 7 report

RMBK-1000 cross section from INSAG-7 report. Reactor core at (1); 1000 ton core lid at (4); steam drums at (8); refueling machine at (18); turbine generator at (32). Note that while certain spaces are intended to contain releases of steam, there is no unified or single, integral containment structure as in most Western reactors.

A test

On April 26, 1986, operators at Unit 4 of Chernobyl were attempting to conduct a fairly unusual test in which the rate of change of water flow through the core, as well as the functioning of certain emergency cooling systems, would be analyzed as some of the pumps putting water through the core slowly wound down in speed. In order to establish the conditions for the test, the operators blocked safety functions in some instances while ignoring the plant computer’s attempts to normalize the power distribution in the core. Delays in the test (caused by the grid requiring power from Unit 4 longer than anticipated before it was tripped off for the test) caused the operators to get the core into an unstable condition (with most of the power being generated at the top, and with relatively hot water entering at the bottom) while determined to complete the test after the need for power was over. It must be said here that accounts of specific control room actions differ—and that not all workers involved survived.

As the time for the test approached, the operators disabled or bypassed several installed safety interlocks that, if actuated, would have interrupted the test. These actions were easily enough taken. At just after 1:20 am on April 26, the test was initiated by tripping the running turbine generator and pushing a separate button to initiate equipment being tested. The plan was to have the reactor scrammed simultaneously, but this did not occur; the reactor scram button AZ-5 was not pushed until about 30 seconds later.

Operators heard “banging sounds” from the area of the reactor, which was probably the initial rupture of tubes in the reactor. Exposing hot, disintegrating fuel to the steam led to an immediate and violent reaction between the metal and steam, raising the pressure in the core structure. Almost immediately a large explosion was heard; it was this that disassembled the core and launched the 1000-ton reactor lid off the top, breaking all the pressure tubes in the reactor. A second explosion was heard shortly—this has been assumed to be the combustion of hydrogen released in the accident.

The reactor was demolished and so was much of its building. Multiple fires had started. The turbine building had been pummeled by debris and was also on fire, threatening the connected Unit 3 equipment areas. Approach to the reactor was impossible because of the high radiation, although two control room operators and two trainees approached or (in the case of the trainees) entered the reactor space and received fatal doses of radiation. Large amounts of radioactive materials were being released because the core itself was essentially exposed to the atmosphere. The most serious nuclear accident in history had occurred.

Chernobyl Unit 4 the morning after the accident, taken from a helicopter.  Note damage to reactor building and turbine building.  Courtesy SSE ChNPP.

Chernobyl Unit 4 the morning after the accident, taken from a helicopter. Note damage to reactor building and turbine building. (Courtesy SSE ChNPP)

First response, and silence

The immediate response, of course, at the scene was to extinguish the fires (with the help of outside fire brigades) and determine the condition of the reactor. Cooling water for the core was put on at a high rate, but sometime later was turned off when it was found that it simply was flooding the lower levels of the plant (without cooling the seriously deranged core much) and the worry was expressed that it might flood the other units. Unit 3 shut down shortly after the accident, as it was immediately adjacent, but Units 1 and 2 operated until the next day. Some areas of the other units were contaminated by the air handling systems spreading material released in the accident. (Much later, nitrogen gas was introduced to the spaces under the reactor to cool it and the melted fuel debris).

As government forces were mobilized, it was determined to attempt to quench the core by dumping materials on it either by helicopter or by hand. Various materials (eventually about 5000 tons) were dumped on the core area over the next weeks through May 10. In fact, this action contributed in an indirect way to releasing material to the atmosphere, it is thought, by first insulating the core and allowing temperatures to increase, which led to a spike in atmospheric releases again several days after the accident. The work was successful in eliminating the chance of any recriticality of the destroyed reactor, however, although a great deal of molten material had poured into myriad spaces below the reactor (where radiation levels were 8000 to 10,000 Roentgens per hour). Between the initial explosion/accident and the quenching work, as many as 31 people died from direct injury or high radiation exposure. These were the first fatalities from a commercial nuclear reactor accident in history—and remain as the only ones today.

What the European neighbor nations first experienced was an increase in detected radionuclides coming in and from the air without any known source on their lands, which was met with complete diplomatic silence by the USSR. Very shortly the secret had to be told, and the USSR admitted that a serious nuclear accident had taken place at Chernobyl.


The Soviet government very quickly responded by condemning the control room operators and plant staff, making statements publicly to this effect and then placing a number of them in prison. Grigoriy Medvedev published a book, entitled Chernobyl Notebook, which carried on this theme of operator error and disregard for safety. The book was published first privately in 1987 and then in France in 1989.

After a short time, however, physical and operational details of the RBMK reactors began to come to light much more than they had before, and even before a year was up some were roundly condemning the reactor design itself as causative. For example, the March 1987 UK Atomic Energy Agency report on the accident specifically called out the positive void coefficient of the reactor at low power levels (a term that means power will automatically increase if water in the core is replaced with steam voids). The report essentially stated that the core was in some conditions unstable and uncontrollable.

By 1991 some of the imprisoned operators had been released and began to tell a story different from that which the old Soviet spokesmen had given—that there had been no procedural violations, that rules which were stated as violated had never existed until after the accident, that interlocks were approved for cutting out in the test procedure, and that the real causes were not due to operator error. The former deputy engineer for Operations at the plant, Anatoly Dyatlov (who set up the test and who was in the control room when the accident occurred), took up the cause of exonerating the operators by publishing widely the opinion that the reactor was in fact inherently dangerous, and that the key fault was the design of the control rods which, when scrammed, first RAISED power briefly before reducing it. This had led at the moment of the pressing of the scram button to a shift in power axially in the core to the bottom; the positive void coefficient (surmised years earlier) caused skyrocketing power in the lower half of the core that destroyed it first, causing an unstoppable series of events leading to the complete demolition of the core. Dyatlov squarely blamed the designers as well as all other people in positions that would have reviewed or regulated the plant designs, saying that the RBMKs should never have been licensed to operate in the first place.

Dyatlov’s point of view is essentially supported by the safety changes made to all other RBMK reactors—changes that began even while he was still imprisoned. Generically, the RBMK type reactor became roundly condemned on the world stage, but even so all of the units around the former USSR continued to operate for many years and 11 reactors of this type operate today, albeit with so many complicated backfits and modifications that they cannot be thought of as being the same as 1986 technology. Those units not in Russia have been shut down.

While many other problems were found technically with the RBMK reactor and plant (including fire protection, ability to localize damage, reliability of core cooling, instrumentation, computer analysis, and many more), these were all secondary to the fact that the actual reactor itself was inherently unstable and dangerous. Lack of any sort of safety culture in the Soviet Union’s nuclear industry, as we would know it today, played a role in this throughout so that some analysts have labeled Chernobyl not as the failing of a specific design but rather in a large scale as an “Organizational Accident” in which the conditions for any such accident existed long before the actual terminating event.

Voluminous reports were naturally generated and issued worldwide (US NRC NUREG-1250 and INSAG-1 as examples) and later had to be revised (INSAG-7, as replacing INSAG-1, for example) in light of discoveries, admissions and revelations, and new analysis. As usual, the reports issued most closely after the event were those most altered, revised or discarded.

The Chernobyl Sarcophagus.  Courtesy SSE ChNPP.

The Chernobyl Sarcophagus (Courtesy SSE ChNPP)

Response, mitigation, entombment

It goes without saying that the officials knew that the plant was releasing radionuclides to the atmosphere, even on the morning of April 27, and shortly the entire nearby city of Pripyat was evacuated. It remains abandoned to this day as no large effort to decontaminate the city has ever been started. A large exclusion zone was set up and about 116,000 persons were displaced by this action. The nearby area in which Chernobyl Units 5 and 6 were being built was more or less purloined by the recovery effort (aided by the mid-1987 cancellation of these units) and many foundations and pits on that site were used to bury contaminated equipment and material.

The famous “Sarcophagus” built over the destroyed reactor over the next several years was intended to last for many more years than it actually did. It was recognized before the middle 1990s that a much more thorough enclosure would be needed, and that a resulting gigantic structure, seen below, is today nearing completion. When finished it will be rolled over the damaged plant encasing it and its previous enclosure.

New containment for Chernobyl Unit 4.  The enormous scale can be judged by comparison with the construction equipment. Courtesy SSE ChNPP.

New containment for Chernobyl Unit 4. The enormous scale can be judged by comparison with the construction equipment. (Courtesy SSE ChNPP)


In the West—where reactors are not of this type, are well contained, and have redundant backup systems and emergency plans, in addition to plant staffs having safety cultures far superior to any in existence in the mid-1980s Soviet Union—the Chernobyl accident has been thought of by some as so completely impossible here as to be without merit to study. Still, there are valuable lessons to be learned that are widely applicable. Among these are the following:

  • No one at any step of the design, construction, operation, administration, maintenance, or regulation processes of the Soviet plants felt as if safety was his or her “number one job” or that “the buck stops here.” The Chernobyl accident, viewed as an “organizational accident,” is a prime example of what will happen in this situation. Indeed, Dyatlov wrote that there were surely many prior times that other RBMK reactors were just as close to disaster as was Chernobyl-4; it just happened there first. The Russians did of course develop a safety culture, and also turned 100 percent to the pressurized water reactor for commercial power.
  • Even though the occurrence of reactor accidents is very small statistically in comparison with the number of reactor-years piled up so far, it is folly to believe that there is no value in providing a fully operable and capable containment for a reactor, designed to handle the maximum possible release of energy from that reactor.
  • Clear and immediate communications are essential, both between a plant site and the government bodies and between nations.


While the initial plan for the Chernobyl plant was to have it be no more decontaminated than the surrounding areas, with the damaged unit and parts of the connected Unit 3 fully entombed, today the plant’s operating company, SSE Chernobyl NPP, is pushing for a different plan. Instead of having what would have been what the company calls a “brown zone,” it wants to decontaminate the entire local area and use some of it for industrial purposes. The company believes that there is money to be made from decommissioning the other units as well as from training on that activity, and that the remote location and installed water and power assets (formerly for the nuclear plants) can serve industrial purposes quite well. It also feels it can reverse the economic burden of maintaining an exclusion zone in the first place.

Meanwhile, plants and animals are flourishing in the exclusion zone, free of disturbance by the former activity and have been widely reported on and studied.

The final chapters on the Chernobyl plant site and the town of Pripyat have yet to be written. Someday there may be wide human activity there again, beyond the decommissioning work on the nuclear plant. If present conditions are any indication, this will come, even if only after many more years.

Administration building, Chernobyl NPP. Courtesy SSE ChNPP.

Administration building, Chernobyl NPP (Courtesy SSE ChNPP)



“Soviet Nuclear Power Plants.” David Katsman, Delphic Associates Incorporated 1986.

NUREG-1250  “Report on the Accident at the Chernobyl Nuclear Power Station” US NRC January 1987

“Chernobyl Design Defects- The British View.”  Nuclear Engineering International, June 1987

“Lessons from an insider’s notebook.” James Varley, Nuclear Engineering International, June 1990.

“No easy answers to Chernobyl questions.” James Varley, Nuclear Engineering International, June 1991.

“How it was: an operator’s perspective”  Anatoly Dyatlov, Nuclear Engineering International, November 1991.

INSAG-7  “The Chernobyl Accident: Updating of INSAG-1.”  International Nuclear Safety Advisory Group (IAEA) 1992

“Why INSAG has still got it wrong.” Anatoly Dyatlov, Nuclear Engineering International, September 1995.

“Soviet Nuclear Plants – VVER and RBMK.”  Research paper by author, privately circulated; October 2015

SSE ChNPP website

______________________________________________________________________________________Will DavisWill Davis is Communications Director and board member for the N/S Savannah Association, Inc. He is a consultant to the Global America Business Institute, a contributing author for Fuel Cycle Week, and he writes his own popular blog Atomic Power Review. Davis is also a consultant and writer for the American Nuclear Society, and serves on the ANS Communications Committee and will serve on the Book Publishing Committee beginning in June. He is a former US Navy reactor operator.


16 thoughts on “Chernobyl Through the Mist of Decades

  1. JK August

    I did the operational analysis response for the PSC Fort St. Vrain reactor in the following quarter of 1986. All the weaknesses in the RMBK design were well known in the West at that time. The performance of the tests themselves demonstrated the absence of anything like the US NRC’s Part 50.59 Process for the control of “Changes, Tests and Experiments.” So tragically, the event confirmed much of the wisdom in the US licensing approach.
    Ironically, the Chernobyl design went far with the concerns of the day to shut down what arguably was the safest nuclear design ever licensed in the world — the High Temperature Helium-cooled Gas Reactor (HTGR). It remains for the future to seriously reconsider these safer designs. This remains a very promising design for nuclear applications in the third world, indeed the entire world.

  2. Jaro Franta

    Good article.
    I am a bit puzzled by the statement, “Exposing hot fuel to the steam led to an immediate and violent reaction between the metal and steam.”
    The implication seems to be that RBMK fuel is metallic, which it is not.
    Moreover, the fuel bundles inside fuel channel pressure tubes are exposed to water/steam during normal operation.
    Evidently, this part could use some clarification.

  3. Will Davis


    While I do not wish to launch a “comment war” on this article, I feel compelled to at least partially express my strong disagreement that the Chernobyl accident was deliberately concocted and/or exacerbated by oil interests, the Soviet Union, or Western Vendors.

    “Demonization” of the design was launched by those who studied the technical details of the reactors outside the USSR as soon as anything useful became available (see the British reference in the article.) Further, Dyatlov is completely correct in stating that the majority of the blame must be placed on those who were in the process that allowed such reactors to be built and operated (this is similar to SL-1 arguments, although the two events and plants as you know have many differences and nuances.) Deficiencies of Soviet-era nuclear plants are well known and documented today of course and weren’t limited to just the pile reactors (q.v. the VVER-440 V-230 design.) The reactor design was moreover proven not safe, and the evidence of that is at least in part the myriad changes made to the other RBMK reactors afterward (probably the most important being the alterations to prevent the “positive scram,” and the addition of many more absorbers in the core to add negative reactivity.)

    No one at that time could possibly have imagined a commercial market for Western reactors inside the USSR. The prospect of a Western reactor sale inside the Iron Curtain at that time was asymptotically close to zero, and there was no huge export market for Soviet plants that anyone would have wished to take over (would Westinghouse have tried to take over Juragua, in Cuba?) This just seems flatly impossible on its face – that Western vendors tried to play this for a sales advantage.

    I have never at any point seen, heard or heard of any credible evidence of anyone having been paid off to blow up this reactor. If you have that (as implied by No. 5 in the first list of your post) I would love to see it. I would imagine Dyatlov, among others, would not have appreciated the prison sentences they received as part of the coverup that would have to have been fabricated.

    All that being said, I do thank you for the comments. They do bring up a very critical period in the history of the USSR, and I am aware that there are many who have written that the Chernobyl accident either triggered or accelerated the collapse of the Soviet Union. It is impossible to separate fully the accident from the fabric of Soviet government and culture and to do so risks misreading or missing altogether some of the important implications of a tyrannical, top down Communist regime which builds technologies whose non-zero risks must be managed. And I think in the final analysis that’s the root of the story here – one of completely (systemically) failed risk identification and management, and not a story of conspiratorial industrial sabotage. But again, I thank you for taking time out to comment.

  4. Rod Adams

    My conspiratorial mind, my belief in the very human tendency to CYOA (cover your own posterior), and my recognition of the number of business & political leaders that have been trained to “never let a crisis go to waste” leads me to a different set of conclusions.

    1. The reactor design might not have been perfect, but it was safe enough in the hands of competent, dedicated operators led by competent, technically astute and dedicated managers.
    2. The operators on duty during the midshift of April 26, 1986 were not competent and dedicated.
    3. The manager on duty was not competent, technically astute, or dedicated.
    4. The plant design demonization was led by western reactor vendors and operators seeking to both expand their markets and protect their existing investments.
    5. It’s possible that a few people in the decision chain deliberately created a situation where the plant would experience a failure. They may or may not have recognized just how catastrophic that failure might be, but they were probably pleased and lucratively rewarded by the results they achieved.

    Many question the logic of number 5 and ask me about motivation. It’s a little complex and convoluted, but then human behavior and motivation often are.
    1. The Soviet Union had a long history of dislike of Ukraine and its native inhabitants. There were several points in history where that led to depopulation efforts that would now be called genocide.
    2. The Soviet Union was struggling mightily under the economic pressure caused by a crash in oil and gas prices in 1986. That price crash severely restricted their national income and was caused by a temporary oversupply in the energy market. Destruction of a nuclear power plant and the subsequent halt to growth in nuclear energy production was one way to address that oversupply situation.
    3. Soviet leaders recognized their Communist paradise was falling apart and they were already scheming for ways to profit from the collapse, including picking up pieces of the state run energy industry for pennies on the dollar.

    Rod Adams
    Publisher, Atomic Insights

  5. Will Davis

    Thanks for these added pieces of information, John! These definitely aren’t all in circulation and they add clarity to this now long-ago event. I appreciate it.

  6. Will Davis

    I have heard nothing specifically about the grad school experiment and I wonder if that was not an erroneous report from the time – considering that many appear to have been printed. However, it appears that if such were conducted it would have at least partially been correct! The reactor did have an overall positive power coefficient of reactivity, driven by the void coefficient, at low power. According to Dyatlov, the accident would have happened exactly as it did (with reactor in same condition) when the scram occurred, whether another test was in progress or not.

  7. Will Davis

    Thank you, Meredith! Perhaps I’d start with Energy Collective if I can figure out how to log in there after the changeover..

  8. Li

    A Clarification:
    In my understanding, Chernobyl test was a reaction to a foreign air-force bombarding a Russian designed reactor in Syria. Cold war confrontation was the 1st trigger.
    They intended to prove that a RBMK reactor fails safe, if grid is taken of by enemy action, similar to the uses of graphite bombs in Serbia by “the good guys”, being able to produce the electricity to run the cooling pumps using its energy in steam, and turbine’s momentum of inertia, in order not to put a backup battery that was expensive those days.
    I have doubts that the plan as designed was safe, but over it comes “corporate culture”, incompetence and arrogance, of the managers, who went outside the test specification, and achieved something “outstanding”… the opposite of their wishful thinking…a disaster.
    Finally their attempt to prove that Russian nuclear technology is perfect, and save $20-40 Millions in a 1MWh battery bank was rewarded by “nature” with a $20 Billion loss, + collateral damage brought to nuclear industry world wide.
    The world’s conclusion = Nuclear is bad! Let’s get rid of it in spite all universe is nuclear and at its physical limits is the most environment friendly power source.

  9. Edward DeLaney

    An excellent summary of the entire event and background leading up to it.
    An important part of this is the studies of health effects on the Russian population and that of other countries. I understand that the effects, except for the immediate responders, are much less than the linear no-threshold theory would predict. The long term effects of low-dose radiation are being vastly over-estimated.

  10. Meredith Angwin

    Will, you have written thoughtful, well-referenced and CLEAR retrospective. And it is hard to achieve all of this in one document! You have done so. Congratulations!

    I completely agree with James Greenidge. This article should be read in the main-stream press. I suggest you send it to the Atlantic Monthly, to some of the places where William Tucker (may he rest in peace) used to publish, and so forth.

  11. James Greenidge

    One excellent article worthy being in National Geographic and Scientific American if not every newspaper science column. It behooves the provinces of Chernobyl and Fukushima to quickly get their populations back — even by fire-sale property inducements — to help quell the wild mutant animal and radioactive desert tales being sow unchallenged by anti-nukers.
    Very excellent report!!
    James Greenidge
    Queens NY

  12. VinceTeofilo

    It was my understanding from contemporary reports at the time [see 1986 IEEE Spectrum ] that a graduate school experiment was conducted which showed the reactor had a positive coefficient of reactivity at low power levels which was only attained by over riding safety algorithms. When it was demonstrated rather then scram the reactor and reset the safety protocols the reactor was allowed to drift in the wrong direction at the reactivity saddle point that was maintained.

  13. Li

    The main learning from history is that : History lesson learned are never learned – and same facts are repeated on and on up to boringhood…
    Same greed, same forceful management was in power in Russia, at Chernobyl, in Japan at Fukushima and in US at WIPP/LANL.
    In LANL, if one asks questions is seen as a threat by the team, so nobody dared to ask what is the difference between an_organic and anorganic (sometime spelled inorganic) cat litter so when some unknown wonder-cats littered that cat litter more than usual on 2014 Valentine’s Day, the “dark” stuff went ka-boom many reports have been written, just to cover-up and nobody dared to ask what’s in fact LANL’s culture, DOE’s culture and with what is it different from Russian culture or TEPCO’s culture?
    This is the magic truth that nobody wants to hear, to understand its roots and take some minor corrective actions as those already taken : UC was not good enough; LANS a conglomerate is not good enough !?
    HC (Holly Crap) – these are just escape goats!
    Something more fundamental is lurking there and have to be found, identified and cured…until then we keep wondering and counting …admiring how nuclear power is fading, leaving behind a mess of nuclear waste, few explosive devices one wonders when and where they will become supra-critical, and tons of bad memories stories, put in a bunch called ” US nuclear legacy”.
    If somebody cares, have to look into this details first apply a cure, and reset nuclear power on its right path for safety, prosperity and development, as the only most ecologic friendly power – when applied not in a rudimentary way like now, just a hot-rod but when we apply it in an advanced manner, near its physical limits.

  14. John Bickel

    Good Article !
    I could add a few minor details lost over time:
    (a) the test originated not from the reactor design bureau (NIKIET), or the plant staff – but from the Turbine Generator design bureau. The stated purpose was to determine circulating pump flow coast-down characteristics during a simulated loss of offsite power with the Main Turbine Generator continuing to power the Circulating Pumps.
    (b) The operators, while trained at the Moscow Power Engineering Institute, were viewed as “Ukrainians” by the Moscow elite – equivalent in the US to saying they were “Hillbillies from the back-woods of Kentucky”.
    (c) If a Design Bureau from Moscow told you to do a test — “you would assume” someone in higher authority had already reviewed the safety implications and determined it to be OK.
    (d) Many of the senior control room staff had taken off early for the May Day Holidays (equivalent to ‘Labor Day Weekend’ in the US) – leaving a less experienced crew to carry out the tests.
    (e) Supposedly there was some type of “incentive bonus” involved in successfully completing the test and recording the requested data for the turbine design bureau.This was one of the key reasons they were fighting to repeat the test in off-normal conditions just as post-trip Xenon-feedback was building in and fighting the low power reactivity control.
    (f) The first fatalities were the equivalent of our plant equipment operators – who were dispatched to the reactor hall after the operators heard the big bangs.
    [I worked as an advisor to the Lithuanian Regulator VATESI from 1994-2004 and regularly did work related to Ignalina 1,2 in Visaginas Lithuania.]

  15. Francesco D'Auria

    One sentence is missing in your picture of the Chernobyl accident: “till today there is no public available calculation that could simulate/justify the energy release during the accident”

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