The Wikipedia discussion of why they were doing the test says “over 6 %”. That may not seem like a lot, but none of that heat is being carried away, so temperature of the fuel elements starts rising immediately. The required flow rate at full power was “45 million litres per hour”, so you “only” need 3 million l/h to remove decay heat (actually, maybe “only” a half million l/h, since the test was intended to be run at 700 MW). That’s still a lot of required flow, with a lot of internal resistance slowing it down as soon as the main coolant pumps kick off.
“Midnight In Chernobyl” is one of the best nonfiction books I’ve ever read, and explains how design flaws, an inflexible and poorly adapting regulatory system, politics, substandard manufacture, corruption and human error led to the accident. It’s also excellent on the human side of the catastrophe.
This offers some useful basics on the RBMK reactor and changes made after the disaster.
Though they actually sent them to a clinic in Belarus that specializes in radiation sickness. Someone was actually thinking straight there, so probably not the idiot who came up with the plan to occupy Chernobyl in the first place.
Yes, I want to join with those who have said that the series was both compelling viewing (you almost wish there were further disasters so we could have a second season (joke)), and largely accurate.
I recall watching a breakdown of the accuracy of the series with a nuclear engineer and a doctor. IIRC the main inaccuracy was a bit of artistic license with how and when people got sick; it wasn’t quite as sudden and dramatic as depicted. And, as already mentioned, that many separate people were merged into a couple of protagonists.
Apart from that though, as crazy as all those events seem, it’s pretty much how it all played out.
Thanks. That is helpful.
And thanks to all the other contributors to the thread as well.
Watch the HBO series, N_P, it is one of the best pieces of docudrama I’ve ever seen. Really worthwhile.
Along with Scott Manley’s excellent video that @Whack-a-Mole posted above, I would also recommend this video: What /Actually/ Happened at Chernobyl - YouTube The whole “graphite tips” thing is one of the main inaccuracies of the HBO series. If after the two videos you’re still wondering about the last push over the edge of the neutron flux and the reaction, we dove into it a bit more here: Chernobyl Control Rod Graphite "Tips"
The reactor powers the turbines (reactor boils water to steam and steam spins the turbines).
The power plant not only powers cities, it powers itself. So, electricity from the turbines is used to power the pumps that push water into the reactor to be turned to steam which spins the turbines which powers the pumps. And so on…
If the reactor is stopped for some reason (such as a SCRAM…and yeah…the reactor can be stopped dead in mere moments) then there is not enough steam to spin the turbines and thus not enough electricity to power the pumps that push water to the reactor. Even when the reactor is stopped it produces a whole lot of decay heat (fission products that decay over time and release heat). Even if “only” 6% of top reactor power (say, 3000 megawatts) that is 180 megawatts of heat…which is a lot and needs to be cooled.
That is why all of these power plants have backup diesel generators. In case the reactor goes offline the diesel generators kick in and power the pumps (and the rest of the plant). They need to keep cooling water flowing or they will meltdown.
But, there is a delay between the reactor turning off and the diesel generators turning on. The Chernobyl test was to see if they could bridge that gap.
One thing I have never seen answered is why the chief engineer Anatoly Dyatlov was so super-keen on seeing the test done to the exclusion of all else.
If the HBO series (which I’ve seen twice) is to be believed, his boss was pressuring him because records had been falsified to show the test done before the plant was “completed”, so they needed to have the test done for real to keep it from causing the boss problems with a promotion he was chasing, which would have opened a promotion for Dyatlov.
It was part of the commissioning process of the reactor, which was built in 1983 and had been operational for months without a demonstration that it could weather a loss of grid power. Reactors 1-3 were older and had gone through that process already. Reactor 4 was also scheduled to be taken offline for refueling after the test, so if they didn’t get it done successfully there would be yet more delay in getting its certification finalized (such as it is).
The Soviet system gave out bonuses, incentives, promotions, and accolades for completing projects on-time and on-budget, and the test was part of the completion of the reactor. It sounds like the forms were signed off on without the test having actually been run, so there was pressure from the plant operators to get it over with so they could move on and not risk their promotions and bonuses (@Seanette beat me to it).
I have read of some push back regarding Dyatlov’s attitude towards the rest of the plant operators as depicted in the HBO series. His confidence in the reactor design and his experience were palpable, but it sounds like he wasn’t as standoffish and threatening as portrayed. Supposedly he even defended the (by then deceased) operators. Regardless, he represents a system where you do not question your superiors, their superiors, or the system itself. Even if Dyatlov didn’t say “you will lose your job over this,” the show had to convey that that’s what would happen to those operators raising concern. It’s the overall narrative of the series after all.
You completely miss my point I’m afraid. I’m aware of all that. You asked:
You seem to be assuming that the only situation where they need to use the diesel generators is where the reactor is shut down and so can’t supply power to the pumps. But what about the scenario where the reactor is at high power but for some reason ceases to power the pumps?
I don’t know anything about this stuff but on the face of it it seems to me that if there was, for example, some sort of major failure in the lines carrying steam from the reactor to the turbines, then the reactor might be at high power and need a lot of cooling but not be supplying power to the turbines, so that the diesel backup generators were required.
Totally concur. Fantastic mini-series. @Northern_Piper, if you’re interested in this topic, you really should see it.
The situation being tested is the electric grid going down, i.e. a loss of offsite power (LOOP). The reactor’s pumps aren’t powered directly by the reactor, they’re powered by the rest of the plant and the electric grid at large. That way if something happened to the reactor or the turbines, there’s independent systems in place to keep the cooling pumps running.
That said, if there was a major blackout that took down the whole grid, the reactors are also immediately shut down because (I assume) they can’t safely handle the quick change in load. If they were to keep running, I don’t think it’s possible to just “dump” the electricity being generated into the ground, or vent the steam to atmosphere without affecting the reactor. I’m just spitballing on that, but as a matter of policy, nuclear plants in the US are required to shut down in the event of a LOOP and cannot be brought back online until grid power has been reestablished, so I figure that was done for good reason.
That all makes sense
But presumably if the reactor was at high power they would shut it down in an orderly fashion rather than SCRAM it, so it would take a few minutes, and the idea is they would rely on the kinetic energy in the turbines to get them through the minute or so before the diesel generators ramped up.
Which was what they were testing, whether that kinetic energy would bridge the gap from loss of power to generators taking over.
Yes I know but I was responding to Whack-a-Mole’s query.
How do you treat radiation sickness?
ETA:
Perpetual motion machine!
Well, they found out. So I guess you could say the experiment was successful.
They did not have time to conduct a proper test. The reactor was too busy exploding.