# what was the worst case scenario for chernobyl **URL:** \ **Category:** Factual Questions\ **Created:** [July 21, 2019, 9:19pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415 "2019-07-21T21:19:09Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [July 21, 2019, 9:19pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/1 "2019-07-21T21:19:09Z")
I’m watching parts of the HBO series on it now. They imply if Chernobyl had melted down into the groundwater it would’ve exploded, causing the other 3 cores to explode. It would’ve made Europe uninhabitable (something like that). Is that a realistic outcome? If the USSR had just tried to pretend nothing was happening and ignored it, whats the worst that could have happened? If the worst case scenario had happened (whatever that is) how many would have died and how much land would’ve become uninhabitable? ---
**Author:** ![UltraVires](https://avatars.discourse-cdn.com/v4/letter/u/ecccb3/32.png) [@UltraVires](https://boards.straightdope.com/u/UltraVires)\ **Post date:** [July 21, 2019, 10:32pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/2 "2019-07-21T22:32:52Z")
I also look to the answer of the OP with interest. ---
**Author:** ![blindboyard](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blindboyard/32/2833_2.png) [@blindboyard](https://boards.straightdope.com/u/blindboyard)\ **Post date:** [July 22, 2019, 3:51pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/3 "2019-07-22T15:51:56Z")
It was the water tanks that were going to explode, not the groundwater. Instant transition to stream due to sudden nuclear pile arrival. After they drained the tanks they started worrying about the groundwater contamination. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 22, 2019, 5:41pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/4 "2019-07-22T17:41:04Z")
This [official report](https://www-ns.iaea.org/downloads/rw/meetings/environ-consequences-report-wm-08.05.pdf) says: > [@](#): > > Sampling of groundwater in the affected areas showed that radionuclides can be transferred from surface soils to groundwater. However, the level of the groundwater contamination in most areas (excluding locations of radioactive waste storage and the Chernobyl Shelter industrial site) is low. Furthermore, the rates of migration from the soil surface to groundwater are also very low. Some areas in the exclusion zone with relatively fast radionuclide migration to the aquifers were found by Shestopalov et. al. (2002) in areas with morphological depressions. Horizontal fluxes of radionuclides in groundwaters are also very low because of the slow flow velocity of groundwaters and high retardation of radionuclides (Bugai et al. 1996). > > Short-lived radionuclides are not expected to affect groundwater supplies, because groundwater residence times are much longer than the physical decay time of short-lived nuclides. The only significant transfer of radionuclides to groundwater has occurred within the Chernobyl Exclusion Zone. In some wells during the last 10 years [sup]137[/sup]Cs-activity concentration has declined whilst those of [sup]90[/sup]Sr continue to increase in shallow ground waters (Fig. 2.57). Transfer of radionuclides to groundwater has occurred from radioactive waste-disposal sites in the Exclusion Zone. After the accident, fuel-containing material and radioactive debris were temporarily stored at industrial sites at the power station and in areas near the floodplain of the Pripyat River. In addition, trees from the “red forest” were buried in shallow unlined trenches. At these waste-disposal sites, [sup]90[/sup]Sr-activity concentrations in groundwaters are in some cases of the order of 1000 Bq L[sup]-1[/sup] (Voitsekhovitch et al. 1996). Health risks from groundwater consumption to hypothetical residents returning to these areas, however, were low in comparison to external radiation and internal doses from foodstuffs (Bugai et al. 1996). ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [July 23, 2019, 2:42pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/5 "2019-07-23T14:42:39Z")
Yeah, I am very curious about this as well. I believe the show said that the steam explosion would have been multiple megatons, which seemed implausible to me, but random intuition isn’t very good. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 23, 2019, 2:46pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/6 "2019-07-23T14:46:18Z")
Wait, there was something that could have gone wrong that they missed? Some engineers must have gotten fired for doing a less than complete job. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 23, 2019, 3:24pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/7 "2019-07-23T15:24:01Z")
> [@Snarky\_Kong](#): > > Yeah, I am very curious about this as well. I believe the show said that the steam explosion would have been multiple megatons, which seemed implausible to me, but random intuition isn’t very good. The physics folks over at Stack Exchange agree with you. It’s extremely implausible. They ended up with a numbers ranging from significantly less than 1 kiloton of TNT to 4 kilotons, which is a few orders of magnitude off from the megaton numbers thrown around in the show. One of the posters there also pointed out that if all it took to make a megaton-level explosion was dropping some molten corium into some water, someone would have tried to do it intentionally and possibly weaponize it long before then. It actually took a lot of effort to create megaton-level explosions. Lots of good details here: > ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [July 23, 2019, 5:02pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/8 "2019-07-23T17:02:32Z")
> [@engineer\_comp\_geek](#): > > The physics folks over at Stack Exchange agree with you. It’s extremely implausible. They ended up with a numbers ranging from significantly less than 1 kiloton of TNT to 4 kilotons, which is a few orders of magnitude off from the megaton numbers thrown around in the show. > > One of the posters there also pointed out that if all it took to make a megaton-level explosion was dropping some molten corium into some water, someone would have tried to do it intentionally and possibly weaponize it long before then. It actually took a lot of effort to create megaton-level explosions. > > Lots of good details here: > [thermodynamics - How large would the steam explosion at Chernobyl have been? - Physics Stack Exchange](https://physics.stackexchange.com/questions/480113/how-large-would-the-steam-explosion-at-chernobyl-have-been) Some of lower voted answers suggest that the water could have acted as a moderator and initiated a nuclear explosion, not just flashing the water to steam. seems likely though. Looks like the megaton claim comes from here: [Extract: Voices from Chernobyl by Svetlana Alexievich | Energy | The Guardian](https://www.theguardian.com/environment/2005/apr/25/energy.ukraine) Ok, secondary question. Lets say there is a steam explosion, would that have left Kiev, Minsk, and all the area between uninhabitable? What if the nuclear explosion was possible? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 23, 2019, 5:04pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/9 "2019-07-23T17:04:58Z")
Why are people positing a steam _explosion?_ A genuine explosion would require one of two things: Option A: a slower transfer of large amounts of heat to a body of liquid water contained in a pressure vessel, raising its temperature to well above the boiling point before the vessel ruptures, resulting in a BLEVE. Option B: a near-instantaneous transfer of large amounts of energy to a body of liquid water, raising it all to a temperature well above the boiling point before it (the liquid water) can get out of its own way. Option A? There was mention of water tanks, but if the arriving corium is energetic enough to raise the threat of a megaton BLEVE, wouldn’t it melt or otherwise damage whatever part of the tank it was in contact with? Wouldn’t there have been blowoff valves/plates to vent these tanks before a BLEVE is threatened? Option B is right out. You can’t heat such a large mass of water so quickly. An unlisted option is an actual nuclear criticality explosion somehow happening when the corium reaches the water. like [Oklos.](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor#Mechanism) Except there’s no mention of explosions associated with Oklos: it goes critical, heats up, boils the water away, and cools down, and the water returns, and the cycle starts again. ISTM something similar could be possible during a major nuclear incident like Chernobyl. It might generate a whole lot of radioactive steam over time, but not any sort of mechanically destructive explosion. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 23, 2019, 6:20pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/10 "2019-07-23T18:20:03Z")
There’s also the effect whose name escapes me, that explains why beads of water dance around on a hot frying pan. The heat creates a steam layer which actually insulates between the extreme heat and the liquid water, slowing the evaporation process. I imagine the same thing happening here. The initial failure would be “China Syndrome”, where the overheating core melts down into the earth. (all the way to China, hence the name). The flaw in this is that the suggestion would be that the more material encountered and melted, the more material melted into and diluted into the core melt. At a certain point, the core would be so dilute the reaction would slow and stop (concentration of uranium gets less and less pure, less reaction). If it did reach groundwater first, would it reach as a flat melt the size of a football field and flash it all into steam at once or a more irregular shape where a few fingers of it hit water first and create a layer of steam to push past the rest of the melt, creating a steam layer between? Regardless, we are talking steam explosion not nuclear. Giant steam clouds of water contaminated with nuclear byproducts, not a megaton explosion. ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [July 23, 2019, 7:29pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/11 "2019-07-23T19:29:06Z")
> [@md2000](#): > > There’s also the effect whose name escapes me, that explains why beads of water dance around on a hot frying pan. The heat creates a steam layer which actually insulates between the extreme heat and the liquid water, slowing the evaporation process. I imagine the same thing happening here. > **[Leidenfrost effect](https://en.wikipedia.org/wiki/Leidenfrost_effect)** > > The Leidenfrost effect is a physical phenomenon in which a liquid, close to a solid surface of another body that is significantly hotter than the liquid's boiling point, produces an insulating vapor layer that keeps the liquid from boiling rapidly. Because of this repulsive force, a droplet hovers over the surface, rather than making physical contact with it. The effect is named after the German doctor Johann Gottlob Leidenfrost, who described it in A Tract About Some Qualities of Common Water. ---
**Author:** ![Precambrianmollusc](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/precambrianmollusc/32/63_2.png) [@Precambrianmollusc](https://boards.straightdope.com/u/Precambrianmollusc)\ **Post date:** [July 23, 2019, 7:56pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/12 "2019-07-23T19:56:44Z")
> [@md2000](#): > > There’s also the effect whose name escapes me, that explains why beads of water dance around on a hot frying pan. The heat creates a steam layer which actually insulates between the extreme heat and the liquid water, slowing the evaporation process. I imagine the same thing happening here. > > The initial failure would be “China Syndrome”, where the overheating core melts down into the earth. (all the way to China, hence the name). The flaw in this is that the suggestion would be that the more material encountered and melted, the more material melted into and diluted into the core melt. At a certain point, the core would be so dilute the reaction would slow and stop (concentration of uranium gets less and less pure, less reaction). If it did reach groundwater first, would it reach as a flat melt the size of a football field and flash it all into steam at once or a more irregular shape where a few fingers of it hit water first and create a layer of steam to push past the rest of the melt, creating a steam layer between? > > Regardless, we are talking steam explosion not nuclear. Giant steam clouds of water contaminated with nuclear byproducts, not a megaton explosion. Leidenfrost effect . ---
**Author:** ![Enola\_Gay](https://avatars.discourse-cdn.com/v4/letter/e/3ab097/32.png) [@Enola\_Gay](https://boards.straightdope.com/u/Enola_Gay)\ **Post date:** [July 23, 2019, 8:49pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/13 "2019-07-23T20:49:03Z")
Off topic, but a fun fact: The fictional movie “The China Syndrome” premiered 12 days before the nuclear accident on Three Mile Island. And as I understand the accident at Chernobyl, the use of graphite in their reactors (in order to save money) was a major contributor to the disaster. They have since retrofitted all the nuclear power plants in the former USSR. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 23, 2019, 9:13pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/14 "2019-07-23T21:13:43Z")
> [@Enola\_Gay](#): > > And as I understand the accident at Chernobyl, the use of graphite in their reactors (in order to save money) was a major contributor to the disaster. They have since retrofitted all the nuclear power plants in the former USSR. It is true that graphite can catch fire, but does that in and of itself make them unsafe? Note that there are still loads of graphite-moderated reactors in use in the UK, not to mention all the RBMK reactors in Russia. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 23, 2019, 9:56pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/15 "2019-07-23T21:56:55Z")
> [@Enola\_Gay](#): > > And as I understand the accident at Chernobyl, the use of graphite in their reactors (in order to save money) was a major contributor to the disaster. They have since retrofitted all the nuclear power plants in the former USSR. Specifically, it was the use of graphite tips on the control rods. The main cause of the accident was getting the reactor into a state where they had almost no control over it. They were attempting to do a safety test, simulating a loss of grid power. The idea was that if the grid power fails, the cooling pumps would stop, and the reactor would melt down. The point behind the safety system was to use the momentum in the generator turbine to power the pumps for the minute or so that it took for the backup generators to come online and take over powering the pumps. They had never successfully tested this system. When they went to do the test, it was at the end of the month when everyone needed to meet their production quotas, so the folks in charge of the grid complained that they wouldn’t have enough power. So instead of doing the test, they postponed it, but they kept the generator in a low power state. This produces xenon gas, which poisons the reactor. At higher power, the xenon gets blown off and isn’t a problem, but because they ran the reactor for so long at a lower power state, the xenon built up. They ended up pulling most of the control rods out to compensate for the xenon poisoning, which left them with very little control over the reactor. So up until this point, it’s all human error screwing the pooch. Where the graphite comes into play is that in this type of reactor, even if you totally screw things up, there is a safety button. If you press it, all of the control rods go back into the reactor and stop it. So it’s fairly idiot proof. And these guys were basically being idiots. The problem with the graphite tips though is that when you first insert the rods, the graphite increases the reaction. Then, when the control rods are more fully inserted, the control rods do their job and slow the reaction down. The engineers apparently didn’t know about the graphite tips causing a momentary surge when the rods are inserted, so when they realized they had not only totally hosed their test but had also totally hosed the reactor, they pressed the safety button, the graphite tips went in first, and the reactor power spiked and blew the whole thing up. While there is definitely a point to be made that the graphite tips were a bad thing (and they have since been replaced in similar reactors), if they hadn’t operated the reactor in such a way as to completely poison it and get it into a fragile state with barely any control rods in it, they wouldn’t have needed to rely on the safety button to try to get them out of it. It’s kinda like racing down a hill, stomping on the gas, disconnecting your brakes, then finding out the hard way that your emergency brake actually hits the accelerator before applying the brakes. Yeah, that emergency brake is a problem, but you shouldn’t have gone racing down the hill and disconnecting the brakes in the first place. I wouldn’t call the graphite tips so much a major contributor to the accident as I would call them the final nail in the coffin. If they had done the test as designed and hadn’t poisoned the reactor, they would have never gotten the reactor into a state where they needed to press the safety button. It’s a long chain of events that ended with the graphite tips spiking the reactor’s power output and causing the accident. A break anywhere in that chain would have prevented the explosion. > [@DPRK](#): > > It is true that graphite can catch fire, but does that in and of itself make them unsafe? Note that there are still loads of graphite-moderated reactors in use in the UK, not to mention all the RBMK reactors in Russia. Graphite is still used as a moderator. It’s only the graphite on the tips of the control rods that was changed out so that the safety shutdown wouldn’t blow up the reactor if they managed to get the reactor into a screwed-up state like they did at Chernobyl. ---
**Author:** ![yo\_han\_go](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yo_han_go/32/130_2.png) [@yo\_han\_go](https://boards.straightdope.com/u/yo_han_go)\ **Post date:** [July 24, 2019, 12:30am UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/16 "2019-07-24T00:30:54Z")
Chernobyl was basically fizzled Hiroshima type event. Still it yielded 0,5 KT, but it most of that energy was not a blast. Remember that glowy thing in E1 going straight up? That was no laser show. It could reach similar critical mass when that hot radioactive blob reached basement and then underground water. But this time, the rest of the plant would probably gone into the air too. Or at least into way serious ruins. So yes, much worse. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 24, 2019, 1:45am UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/17 "2019-07-24T01:45:38Z")
> [@engineer\_comp\_geek](#): > > Graphite is still used as a moderator. It’s only the graphite on the tips of the control rods that was changed out so that the safety shutdown wouldn’t blow up the reactor if they managed to get the reactor into a screwed-up state like they did at Chernobyl. If by “changed out” you mean “lowered so it hangs 125 cm lower”, then yes. The “new” manual control rods have the same graphite tips of the same length, but the water column at the bottom of the core when the rod was withdrawn has been eliminated. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 24, 2019, 2:05am UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/18 "2019-07-24T02:05:18Z")
> [@yo\_han\_go](#): > > Chernobyl was basically fizzled Hiroshima type event. Still it yielded 0,5 KT, but it most of that energy was not a blast. Remember that glowy thing in E1 going straight up? That was no laser show. > It could reach similar critical mass when that hot radioactive blob reached basement and then underground water. But this time, the rest of the plant would probably gone into the air too. Or at least into way serious ruins. So yes, much worse. I have not done even back-of-the-envelope calculations, but I have read that such criticality excursions are much less destructive than however many pounds or tons of actual TNT, since most of the fission energy is deposited as heat rather than as kinetic energy. I understand that an additional steam explosion was, at least initially, taken into account as a potential risk and therefore personnel risked their lives to drain all the water below the core, cool down the soil, and related activities. “Glowy thing going straight up” sounds like some radiation-related phenomenon, but even a ridiculously lethal radiation field is not the same as a “blast”. I mean, you’ll die quickly after being bombarded by subatomic particles, but you wouldn’t feel even a gust of wind. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [July 24, 2019, 7:35am UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/19 "2019-07-24T07:35:46Z")
> [@Enola\_Gay](#): > > And as I understand the accident at Chernobyl, the use of graphite in their reactors (in order to save money) was a major contributor to the disaster. They have since retrofitted all the nuclear power plants in the former USSR. Actually [Vlogbrothers has pointed out that the design](https://www.youtube.com/watch?v=hIGtTImeYU4)was not to save money, but a feature of the very high efficiency of the design. Basically they did everything as badly as they could have… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 24, 2019, 2:20pm UTC](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415/20 "2019-07-24T14:20:23Z")
Why would anyone ever use graphite as a moderator, considering that water is an even better moderator, and just about the cheapest substance on the planet? [Next page](https://boards.straightdope.com/t/what-was-the-worst-case-scenario-for-chernobyl/837415.md?page=2)