The flaws with the reactors were not only in the design, but the implementation of some important safety features. In the case of something really horrendous, the system was designed with a maximum design-basis accident button. This button, which was supposed to run through the main system and trigger several emergency systems, was rerouted not to work as designed as to avoid a heat shock in the reactor. In order to produce a “clean” test, several other mistakes were made. One of which was the fact that the test was performed while the reactor was still live. Another mistake was that the emergency water feeds were turned off and locked shut. The triggering mechanism in the emergency systems was disabled so that a second run on the test could have been made in case of failure.
The program that led to the accident was supposed to have taken place on April 25th during the day. At the request of a Kiev load controller, it was delayed until the night shift. It was begun by one team an hour before the midnight shift came on. The test included running down the reactor in order to test the efficiency of the turbines from the time the main power was shut off until the emergency generators came online. It would determine if the turbines could produce enough inertial energy to power the station until the generators kicked in.
With the reactor still functioning and the maximum design-basis accident features disabled, the reactor reached a dangerously low power level. In the RBMK reactor, when the power emissions drop below a certain level, the reaction begins to be poisoned by a buildup of certain elements, such as xenon and iodine. Where normally the emergency systems would have shut the reactor down, it was allowed to drop to 30 megawatts. At that level, it was extremely difficult, if not impossible to control and stabilize.
When the power fell to the low levels, one of the engineers notified Dyatlov what had happened. Dyatlov told him to bring the power back up. The engineer, Tuptonov, refused and was backed up by the other senior engineer. The only safe decision was to power down the reactor completely and resume the test twenty-four hours later. Dyatlov went ballistic. He threatened them, swore at them, bullied them and threatened to replace them with others and even fire them. His manipulation finally yielded the desired result…they caved in.
In order to create additional power, it was necessary to raise some of the boron control rods. By safety specification, it was mandatory that a minimum of 28 of the 210 rods be maintained at all times in the core. At the moment of decision, that is all there were in the core. When the reactor exploded, there were only 18 left.
With the extraction of the rods, the power levels rose to about 200 megawatts before it leveled out due to the poisoning in the reactor. It was still 600 less than the minimum operational reactor reserve. The engineers were scrambling to maintain proper levels on the water circulation, the steam pressure and the power levels. At this point, 2 minutes from the explosion, they still could have stopped it. All it would have taken was for them to carefully power down the reactor.
About 30 seconds to the explosion, the main circulation pumps began to fail. The water circulating, as part of the test, was kept close to saturation. With the increase in power and temperature, the water began to steam, killing the pumps. With that, water levels decreased and the water began to boil inside the reactor creating more steam, thus more power. The positive void coefficient was in effect.
Tuptonov reported a power surge to Akimov, the other senior engineer. Akimov, against all judgment and training, engaged the emergency power reduction system. It proved to be a fatal mistake. The emergency power reduction system involved the lowering of all boron control rods into the reactor simultaneously. You may think that this a good thing, no?
The problem was another odd design quirk. The 23 foot rods were not completely boron. The tips of the rods were actually made of graphite with an empty section before the boron. Thus, when rods were inserted into the core, they produced a power spike. Not a problem in a reactor working within normal parameters, but in a superheated reactor with fluctuating power levels, it was the end.
For more reading, see:
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MSN Encarta article
Nova Online timeline
Acute Radiation Syndrome: A Fact Sheet for Physicians
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Hi. You are quoting this out of Medvedev book. He is full of shit. He was not involved in day to day operation at Chernobyl, at most only being part of the supply chain. He wasn’t trained to operate an NPP, nor is he qualified to speak about anything. Oh, and his clame of being sick after receiving a dose of radiation is bull too – when pushed to prove it, he couldn’t (as he never “recieved a dose”).
Thus, I have a number of questions about validity of your account above.
Got any references for: “When the power fell to the low levels, one of the engineers notified Dyatlov what had happened. Dyatlov told him to bring the power back up. The engineer, Tuptonov, refused and was backed up by the other senior engineer. The only safe decision was to power down the reactor completely and resume the test twenty-four hours later. Dyatlov went ballistic. He threatened them, swore at them, bullied them and threatened to replace them with others and even fire them. His manipulation finally yielded the desired result…they caved in.”?
This is not how I read either http://lib.ru/MEMUARY/CHERNOBYL/dyatlow.txt (Dyatlow’s own account), nor accounts of Leonid Toptunov (note correct spelling, please)(Operator) or Alexander Akimov (Head of night shift of Chernobyl-4). Akimov was head of the shift, and only he could have ordered Toptunov anything any way. Yes, both Toptunov and Aikmov died from overdose, but not before their statements were recorded by the investigators, and used in Dyatlov’s trial.
The quip about unqualified personnel that I see all the time is mostly bullshit too. Dyatlov, for example, transferred to Chernobyl from a nuclear submarine shipbuilding plant at Komsomolsk-na-Amure in 1973. Worked at Chernobyl NPP for over 12 years. If 12 years of experience is not qualified, what is?
Note that in 1991 IAEA reworded the causes of the accident, laying heavier blame on the design flaws of RBMK then on the operating personnel.
“By safety specification, it was mandatory that a minimum of 28 of the 210 rods be maintained at all times in the core.” Again, based on how I read RBMK operating manual, until Chernobyl, safety specification was specifying 15 fully inserted rod equivalents. After Chernobyl, safety specifications were amended to minimum of 75 control rods (out of total of 179 control rods). Reference: http://www.reactors.narod.ru/rbmk/03_rbmk.htm and again, Dyatlov’s account, http://lib.ru/MEMUARY/CHERNOBYL/dyatlow.txt
“At this point, 2 minutes from the explosion, they still could have stopped it. All it would have taken was for them to carefully power down the reactor.” Medvedev wrote bullshit again, and you are repeating it. Major part of the problem was the design of the emergency shutdown rods. At this point, the way to safely recover would have been to bring the reactor back to full power, and then shut it down. Hardly seems that powering reactor back up, to shut it down is part of “carefully powering it down”.
“Tuptonov reported a power surge to Akimov, the other senior engineer. Akimov, against all judgment and training, engaged the emergency power reduction system.” Buddy, you have a reactor going over-critical at a much higher speed then you expected (note that “critical” doesn’t mean “nuclear”, just means that it emits more then 1 neutron per each neutron collision, and thus speed of the reaction is increasing, with positive net energy production. Also note that over and sub-critical change happens exponentially), and you are about to go nuclear. Automatic Emergency Shutdown system was designed to operate if the power output was to double in 20 seconds, so it would have triggered at that point any way.
*sigh*
Based on my reading of witness accounts, and my current understanding of what actually happened, I see errors virtually in every paragraph above.
You got served Josh!
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wikipedia is listed as a source. That could be the bad information.