How Chernobyl Exploded - PART TWO: The Power Drop

It is now midnight on April 26, 1986, the fifth shift has taken control of Chernobyl unit 4 and in 84 minutes the reactor they are operating will be destroyed. The decisions they make unknowingly will determine the fate of the reactor. Now let's analyze the first one. night shift time to recap the situation we ended up with at the end of April 25, we have a 10 hour delay for the turbine reduction experiment. Delayed vibration measurements on the same turbine required for reduction experiment operators who have not performed this experiment. Before the poisoning by Zenon, which had largely been reversed after the

power

reduction on the morning of April 25, other experiments were scheduled to take place in the reactor, what we are about to follow is what I think it is the most accurate description of the The events that led to the Chernobyl disaster almost immediately we are about to encounter the first controversial moment in the fate of the reactor when the shift change occurred.

The

power

of the reactor was at 760 megaw of thermal output five minutes after midnight, the power had already fallen to 720 megaw and was continuing to decrease. Consulting The Rundown's procedures guide we can see that the program requires a power of between 700 and 1000 megaw, so why do they continue to fall? A few reasons have been put forward for this, including Uding Topov's inability to keep up. the power

drop

during the complicated handover or the general poisoning of Zenon, but the real answer seems to be that it was deliberate 5 minutes after midnight, an order by Akimov's order is written in the operations log to start a power reduction again , reasons why such a power reduction would be initiated are seemingly limitless Yuri Treb reported at the trial that he saw Dyatlov demanding Akimov carry out this power reduction to which Akimov protested although it is worth noting that Tgab was just reading lips At that time, Diov himself also accused Boris Roskin, the boss.

The shift supervisor of all units had an argument with Akimov that caused a power outage. The Union Research Institute for the Operation of Vn i a s Nuclear Power Plants prepared its own report on the accident based on the testimony of the operators of Moscow Hospital Number Six. The power

drop

was associated with mitigating the consequences of a pressure wave in the drum separators when the summary began, they later stated that this was the correct decision. What is corroborated in most of the witness testimony is that Dyatlov demanded that Topov hurry up and complete the power reduction at this time.

At this moment Topov is being observed not only by superiors Akimov and Dyatlov, but also by the shift supervisor of the previous shift, Yuri Treer, as well as Victor Proskuryakov and Alexander Kavv, two senior engineers in reactor control practices who are At the end of the year, even some people on Unit 4's shift had decided to skip their positions for the time being to observe, like Mel Elin, others had stayed on the previous shift, like Sergey Gazin, however, Topton's job became more complicated than usual. During these power reductions, such as on April 25, a representative from the Nuclear Physics Laboratory would be present using a computer program to help reduce power while ensuring the operating reactivity margin, the equivalent number of control rods inserted in the core would not fall to a low level. levels due to the buildup of Zenon, unfortunately for Topton, the specialist who was supposed to be on duty that day, anat chernev was absent because he had been mistakenly told that the reactor was already shut down, this means that Topov was effectively reducing power without power see the omm here again we have another point of controversy according to many people in the trial diatlov was present in the control room throughout the shift but he himself and some others outside the trial maintain that he was absent from time to time since many of the present at the trial were threatened and forced to adopt a negative stance towards the outlaw.

We will follow a version of events with a small detail. Diatlov actually leaves the control room to observe several areas that will need maintenance before closing, whether he believes it or not. Whether or not, Diatlov will not play a major role in the upcoming events with Diatlov out of the room and the pressure raised from the back of Topov, he continues to lower the power under less supervision and comes down while people look at the other desks to observe his progress as the reactor approaches a crucial stage here when the power approaches 500 megaw when topov disconnects the local automatic control a problem occurs inside the reactor which i will try to make as simple as possible there are three groups of automatic control rods inside of the reactor that are used to keep the energy stable by withdrawing or introducing it if the energy drops or increases too much, respectively, the first of them connects and detects that the reactivity in the core is lower than the power level at which the bar is configured automatic control, this causes the four control rods in the group to withdraw completely, then the second group of control rods connects and this time the imbalance in the core is so extreme that they cannot move at all and the third group, which acts as a reserve, is also not connected, so now there are no automatic movements.

Regulators work on the core at this point, 28 minutes after midnight, something not yet explained definitively occurs in the core, causing a dramatic decrease in power production. It is generally accepted that the Zenon buildup was not due to the events of April 25, which were almost completely authorized at this point, but from this 1600 megaw power drop performed in the absence of computer guidance played some role; However, it is also well established that this would not be enough to cause such a rapid drop in power, perhaps the most likely explanation is a small forgotten quirk in the rbmk, so all the self-propelled rods were control rods that were They were inserted or removed spontaneously at full speed, no less inside or outside the reactor.

Soviet scientists, of course, were aware of this and had created multiple safety devices for the retraction of the control rods. but there was little or nothing left for the insertion of the control rod, a very rapid collapse in power occurred as Topton could only watch as multiple emergency signals appeared on the panel in front of him and the emergency protection systems that put on standby quickly they fell so low. that the automatic regulators could not be brought back online and Topov began a very rapid adjustment of the automatic power regulators to try to align the set points with the output of the new reactor so that the automatic regulator would start working again and then the other groups. it would no longer be stuck and could not move by the time this was done it was too late the reactor power had dropped so low that the neutron count had fallen below the near zero range many people have claimed that the number 30 megawatts appears here, Although this has never been definitively proven and now Topov Akimov and Treub are left with what would initially appear to be a difficult decision about what to do next; some people would assume that the experiment would simply have to be abandoned at this point because of the zenom pit they found.

They were about to fall, but as Trob knew with more experience controlling the reactor under his belt, if they were fast enough to remedy the situation, then they could turn the power back up and if the control rods remained at safe levels, then everything It would be good. The aforementioned Union Research Institute for the Operation of Nuclear Power Plants would also evaluate increasing the power here as the right decision. Some witnesses seem to suggest that Topov however had doubts about increasing the power and did not want to do it, the reason why is quite simple and what we mentioned just a few seconds ago the Zenon pit apparently aware of his lack of experience did not want to increase the power. power at least not alone so tregub exchanged places with akimov so he stood in front of the selection panel and with the help of topov the two began to select rods to take out of the reactor.

Topton's lack of experience quickly became apparent as he would sometimes begin to pull the control bars unevenly and Trob would have to point out which bars to move and very slowly, the level of reactivity began to rise again to a level in the one that could be recorded and meanwhile problems were still developing in all the other panels due to the power drop for Stoia Chuck, the power drop had caused a large drop in the flow of steam coming out of the reactor. , this was now causing the pressure in the steam separators into which the reactor steam flows, as well as the level of water contained within to prevent an automatic shutdown.

He quickly lowered the minimum pressure and waited for Topov to regain control and in the end the turbine desk, Kershen obliged, now had to watch as the steam supply to turbine 8 plummeted, about which he could do absolutely nothing. and then both the turbine analysis and the vibration experiments would be doomed to failure razim davetv, the deputy head of the turbine shop for the operation had to intervene to make sure the turbine did not shut down and took him through a list checking the last minute steps to follow until DOA and then DLo returns to the room quite aware that something went wrong due to the fact that there are now five people trying to increase the power of the reactor, which at this moment is stuck in around 50 megawatts, Akimov rushed over and explained that the reactor's power had dropped to 30 megawatts and that they were now trying to increase it.

DLo, for his

part

, didn't seem to care much. for this, according to all available witness testimony, there were no raised voices and when aimof told him that they wanted to increase the power to only 200 megaw, outlo agreed, it is worth noting that this lower power level does not affect the test in any way, since the experiment is based on the time it takes for the turbine to stop spinning, which does not change at different power levels, meanwhile, now, 41 minutes after midnight, turbine number 8 goes offline of the reactor and finally runs on Idol for a while. of the vibration experiments and would not reconnect to the reactor for another 35 minutes, shortly after they managed to reach 160 megawatts or 5% of the reactor's thermal output and turn the automatic regulators back on, now the reactor power It was increasing again at a comfortable and too fast rate.

At some points, as more water boiled in the core and the positive vacuum coefficient made itself felt, this would lead to automatic regulators being inserted again to compensate, but there were more problems for operators trying to balance all these problems to prime . the Scala computer system to record new summary values ​​the sediment program recording reactor parameters was turned on repeatedly as a new magnetic tape was inserted with this turned off the operators are temporarily controlling the reactor blindly now in several ways. They were without the Nuclear Physics laboratory and its reactor program now for the next 20 minutes they said that the operators have to deal with the lack of updated readings from the Prisma program on the Scala computer that provided guidance to the operators on how to operate the reactor and your devices. that calculated the operating reactivity margin would not work because the power was too low and ultimately they did not know what the new Zenon distribution in the core would have changed during the power drop 15 minutes earlier even though the operators could not rely solely in the side ionization chambers to estimate the power.

This mode of operation had never been limited or prohibited by the designers or engineers who created the RBM. The operators reportedly had some mechanism to work out an approximate operating reactivity margin in the control room using a slow data logging system that would increment the value on a screen that Andov checked semi-regularly against hundreds of other data points. to keep the reactor in balance. treb 2 looked and saw a number around 19 and falling slowly but still clearly up. The lower limit of many of these inserted rods appears to be the automatic regulators that counteract the increasing positive vacuum coefficient at about 1:00 AM. m., the power output reached 200 Mew and the job of the automatic regulators went from helping to increase power to maintaining it. as stable as possible aroundthat number, as Treg would say he didn't like that 200 megawatts simply because of the low power, but he had to accept the order and move on, so he went back to Kersin Bal and the turbine desk to see what was going on. was going to take place there during the experiment and now Topov was again alone at the controls the atmosphere in the control room was calm and relaxed the reactor power is stable with a permitted number of control rods inserted in the reactor there are 24 minutes left until the destruction