[jacquesm]

From what I know about it whether or not the core blew up (again, a small part of it blew up in the beginning of the incident and spewed radioactive graphite all over the site) was a dime on its side, the core was well underway towards landing in the water underneath it, the resulting steam explosion could have thrown all of the core all over the surrounding site. That it didn't happen is due to the heroics of a couple of people who never really made a big deal of it, they went underneath the reactor core to manually open the valves that drained the basin.

[garmaine]

This is correct. However the writers for the show played it up to be much larger than that. In one of the episodes Gorbachov asked how big the explosion would be, and the reply was somewhere in the multi-megaton range IIRC, complete with a description of the predicted damage to the surrounding area equivalent to a major nuclear blast.

The biggest steam boiler explosions in history were still many orders of magnitude less than that, and those were purpose-built pressure vessels. The core wasn't going to drop into a pressure vessel, just whatever makeshift containment they had enacted at that time. Had the core come in contact with the water it would have converted a large chunk of it into steam, which would within moments blow open whatever cracks or leaks existed in the containment, blowing a lot of radioactive rubble into the surrounding environment.

That would have been a huge setback, but nothing near a multi-megaton nuclear explosion.

[TheOtherHobbes]

The problem wasn't the immediate explosion but the huge cloud of hyper-radioactive fallout it would have produced.

Chernobyl still managed to poison large areas of Europe, but the effects were mercifully localised and temporary.

A steam explosion would have increased those effects and the areas they affected by some orders of magnitude.

[jacquesm]

Temporary is a bit of an understatement, to this day there are large numbers of people in the Ukraine and in Eastern Poland as well as areas of Russia that ended up with Thyroid cancer due to this.

[garmaine]

Nobody knows that. That’s pure speculation based on the linear no-threshold model.

[lostlogin]

It’s not conclusive it’s far from speculation.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6535271/

[jacquesm]

I think that needs a 'but' in there somewhere, and for Eastern Poland/Ukraine the figures are quite a bit higher than for Turkey.

See: https://pubmed.ncbi.nlm.nih.gov/14752799/ and many other studies done with similar objectives such as https://www.medpagetoday.org/meetingcoverage/ata/54237?vpass... . It is not something that sits well with various politicians because the liability question was never really answered and so this is just another inconvenient truth.

[garmaine]

I'm not debating that. I'm just saying it would not have been a multi-megaton hydrogen-bomb-like explosion physically destroying not just the plant, but the surrounding city as well, like the characters said it would be on the show.

[jacquesm]

Indeed, in fact if that steam explosion had happened it would have likely reduced the chance of the core going critical rather than increased it. It still would have been pretty bad though, especially given that they didn't really have a good way of cleaning up the highly radioactive graphite other than to have guys pick it up by hand...