A simplified analysis of the Chernobyl accident (2021)
1–10 of 31 posts
Re: A simplified analysis of the Chernobyl accident (2021)
#2The technical reasons why Chernobyl exploded when AZ-5 was pressed were only half of the reasons for the disaster.
The other half of the reasons Chernobyl failed were human reasons.
It is very important when analyzing large systematic failures to not leave these things out.
Re: A simplified analysis of the Chernobyl accident (2021)
#3> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity.
I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place.
For example, having one section just arbitrarily xenon-poisoned, while another is arbitrarily too hot.
Re: A simplified analysis of the Chernobyl accident (2021)
#4The technical reasons why Chernobyl exploded when AZ-5 was pressed were only half of the reasons for the disaster. The other half of the reasons Chernobyl failed were human reasons. It is very important when analyzing large systematic failures to not leave these things out.
Yes, the RBMK was not an inherently safe design (in fact was deeply flawed) but it could be operated safely if you didn't deviate from procedures. Which they did, because they were never told about the design flaws (it was a state secret).
Re: A simplified analysis of the Chernobyl accident (2021)
#5> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place. For example…
Yes, essentially this happens. PWRs and BWRs have operating limits on their power shape derived from doing those kinds of analyses.
They’re tend do be more physical than “arbitrarily xenon-poisoned” but represent a variety of extreme and nominal states to form an operating envelope, and then healthy margins are applied on top of that.
Re: A simplified analysis of the Chernobyl accident (2021)
#6> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place. For example…
The disaster was a result of fuzzy testing :-)
https://en.wikipedia.org/wiki/Chernobyl_disaster#Safety_test
Re: A simplified analysis of the Chernobyl accident (2021)
#7The technical reasons why Chernobyl exploded when AZ-5 was pressed were only half of the reasons for the disaster. The other half of the reasons Chernobyl failed were human reasons. It is very important when analyzing large systematic failures to not leave these things out.
To me, Chernobyl is an example of the classic conundrum that engineers cannot possibly think of every single weird thing that could possibly happen so that a perfectly safe anything can be made. It applies to software design just as much as a nuclear reactor. Sometimes it takes a failure to actually happen before something can be made safer. Somethings are just more consequential when they fail making the learning from failure much more expensive.
Re: A simplified analysis of the Chernobyl accident (2021)
#8> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place. For example…
Yes. Reactors now are designed to never have positive feedback loops that can result in uncontrollable power spikes. They do the worst case simulations to prove that.
Russian atomic regulator downright shut down the project to design a light water breeder reactor, saying that it's not going to be licensed. Light water breeder reactors are barely theoretically possible, but they require trade-offs to limit the amount of water within the reactor core. So the trade-offs result in a positive void coefficient. It's supposed to be offset by other safety features, but better be safe than sorry.
Re: A simplified analysis of the Chernobyl accident (2021)
#9> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place. For example…
Yes, it wasn't intentionally, but it was at Ingalina.
Re: A simplified analysis of the Chernobyl accident (2021)
#10The technical reasons why Chernobyl exploded when AZ-5 was pressed were only half of the reasons for the disaster. The other half of the reasons Chernobyl failed were human reasons. It is very important when analyzing large systematic failures to not leave these things out.
Yes, the RBMK was not an inherently safe design (in fact was deeply flawed) but it could be operated safely if you didn't deviate from procedures. Which they did, because they were never told about the design flaws (it was a state secret).
The local engineers were effectively scapegoated by the KGB. It was disappointing to see HBO follow the same lead.