Timeline for Why was there a "point of no return" in the Chernobyl series that ended in the meltdown?
Current License: CC BY-SA 4.0
12 events
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| Jan 9, 2021 at 18:54 | comment | added | Jirka Hanika | @matt_black - That's correct. There were multiple design flaws in the reactor. They were corrigible to the extent, not corrected after their discovery in the Ignalina power plant, not known to Chernobyl operators, and they were corrected after Chernobyl. However, AZ-5 wasn't expected to be used with that many rods in the highest position; that prior configuration was off the safety protocol and the operators knew that. But they probably had no idea that AZ-5 could speed up the reaction briefly (in this configuration in particular), while other people knew that. | |
| Jan 9, 2021 at 13:56 | comment | added | matt_black | The core point of the show is that there was a known instability in the reactor design and a known flaw in the AZ-5 shutdown mechanism that could tip the reactor into a sudden meltdown. But this knowledge had been suppressed so the engineers didn't know about it. they expected AZ-5 to offer a simple rapid shutdown but at least two other incidents had shown it causing a dangerous power spike (one is described in the show during the investigation). Thus the engineers seeing a power spike wrongly thought AZ-5 would stop it. | |
| Jan 8, 2021 at 23:04 | comment | added | Jirka Hanika | And that's because the average distance a single fission neutron travels from fission to fission in RBMK is measured in meters, not in centimeters. The heat up is local, but not that local. HOWEVER, this logic holds only if the power curve was growing only very slow until AZ-5 was pressed. | |
| Jan 8, 2021 at 23:00 | comment | added | Jirka Hanika | At the bottom of the reactor, the control rod columns are kept pretty "cool", such as under 70 °C per the hypothesis of no runaway power incursion prior to pressing AZ-5. The insertion process interferes with cooling of the particular control column, and the first 3 seconds contribute to extra heat near the bottom part of the particular control column. To make these two ill effects feed into each other at full strength you need to be inserting many rods simultaneously, all of them in a similar phase. | |
| Jan 8, 2021 at 22:53 | comment | added | Jirka Hanika | This is a very balanced answer (I haven't seen the show either). Elaborating on possibility 3: If the engineers weren't aware of any substantial power incursion and pressed AZ-5 just to finish their task of the day, then the fastest + lowest risk protocol for shutting down the reactor would have been to initiate rod insertions individually, spaced 3 seconds apart of each other. A rod takes ~18 seconds to fully insert. But only during the first three seconds there's any risk of the particular rod heating up any particular place as a result of its progress. | |
| Jan 8, 2021 at 17:22 | comment | added | iandotkelly♦ | Hey, no worries. It's all good. No attack assumed, just explaining my perspective | |
| Jan 8, 2021 at 17:21 | comment | added | Nobody | @iandotkelly We can disagree on that point, it's meant to justify why I wanted to add another answer, not attack yours. | |
| Jan 8, 2021 at 17:03 | comment | added | iandotkelly♦ | Good answer (+1) .... I would somewhat dispute that my answer presents things as facts that are not known to be true. My answer is based on the reports and the TV show, which is what the question is about. Yes, it is plausible that the AZ-5 was pressed to shut down the reactor after the test - however as wikipedia states,"RBMK designers claim that the button had to have been pressed only after the reactor already began to self-destruct" and this is the plausible chain of events that are dramatized and what the question is about. | |
| Jan 8, 2021 at 16:35 | history | edited | Nobody | CC BY-SA 4.0 |
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| Jan 8, 2021 at 16:27 | history | edited | Nobody | CC BY-SA 4.0 |
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| Jan 8, 2021 at 16:26 | review | First posts | |||
| Jan 8, 2021 at 20:39 | |||||
| Jan 8, 2021 at 16:20 | history | answered | Nobody | CC BY-SA 4.0 |