I am a fission reactor designer from Los Alamos National Laboratory. I have worked on the design of large commercial power reactors (at GE) all the way down to small specialized reactors: I led the design of the successfully tested DUFF and KRUSTY reactors. I also visited the Soviet Union twice in the 1980s (’85 and ’87). Overall, the miniseries depicted the people and ethos of the Soviet Union very well (except for most actors’ teeth). It also did well describing all of the factors that caused the accident, but failed miserably on the radiation effects. I wish I had watched the miniseries earlier to chime in when the debate was trending, but here’s my take.
RBMK Reactor Instability
The only episode that I came close to enjoying was Episode 5, because of the excellent depiction of all factors that played into the accident – an “unstable” reactor design accompanied by a huge number of human errors (mostly in blatant disregard of procedure). The RBMK reactors can be considered unstable because of a large number of competing reactivity coefficients (some positive, some negative) combined with a very strong Xe-135 reactivity worth (as well described with the red and blue placards in Episode 5). The physical size of the reactor, combined with a moderated neutron spectrum, also plays a major role in making the reactor unstable. The average travel distance of a neutron (mean free path) is very short relative to the size, such that opposite regions of the core do not “talk” to each other very well, which also promotes instability.
The Physics that Caused the Explosion
At the time of the explosion the core was net supercritical (power increasing) but the bottom region was highly supercritical (power increasing rather fast). The insertion of the scram rods did probably not increase the reactivity of the overall reactor, but likely did increase the reactivity in the bottom region of the core; which at that point was acting as its own reactor, mostly oblivious to what the rest of the reactor was doing. Shortly after the insertion of the scram rods, the loss of water in the bottom region increased reactivity (via positive void coefficient) to cause a very rapid rise in power (apparently doubling power more than once per second to at least >10 times normal power, which severely damaged the core). It is not 100% certain that the movement of the scram rods were the primary cause of this last reactivity insertion, because the bottom of the core may have already been heating fast enough to cause water to vaporize on its own (but the prevailing opinion, i.e. that the biggest effect was the rods displacing the water with graphite, seems more likely).
Shoddy Soviet Engineering
My wife spent a year living in the Soviet Union and has lots of interesting stories about poor Soviet engineering; noting that the fault was not the actual engineers but the managers – meeting milestones at low cost is what advanced careers, not quality (another thing HBO does well in portraying). Even with the RBMK instabilities, the “poor” rod design (use of graphite tip/displacer/follower) and the blatant human error, an adequately engineered scram system could have saved the reactor; i.e. if the rod insertion rate had been significantly faster and more robust. The slow movement of the rods did not quench reactivity fast enough. As a result fuel damage occurred to distort the geometry and prevent the rods from moving in any further. If the rods could have gotten most of the way into the core within a few seconds after pushing the scram button, the explosion would have been avoided (all modern reactors can do this, as well as the retrofitted RBMKs). Note: when I or others refer to explosion it is not what could be called a nuclear explosion, i.e. an explosion of the fuel, it was an explosion caused by high gas/vapor pressure, initially caused by steam and later by the rapid burning of graphite (and maybe zirconium as well). To make things even worse, this was a high-power unstable reactor with no reactor containment! Terrible, no other country has ever done anything close to that careless. The trial should have also blamed whoever approved design, construction and operation in the first place. The Soviets were asking for it, and their incompetence and disregard crippled the nuclear industry worldwide. So, well done HBO for pointing out all of this.
Good job so far HBO, but…
The problem with the miniseries was the exaggeration of radiation effects; not by factors of 2 or 3, but by factors or 100 to 1,000. Most of the supposedly radiation induced gore was severely overdone (e.g. the spontaneous full-body bleeding or skinless bodies) – there are actual pictures of victims of Chernobyl, but nothing gory. The bloody cow massacre was exceptionally ludicrous. On the other hand, dose release comparisons to Hiroshima were accurate (Chernobyl released several hundred times more radioactivity), but totally misleading; the deaths and illness caused by Hiroshima radiation were far worse than Chernobyl (because far more people were exposed to high dose). If you want to fixate on raw numbers, consider that the ocean naturally contains well over 100,000 Chernobyls of radiation (over 10 million Hiroshimas), but of course that is misleading too.
Killing the Continent?
Several quotes by our trusted expert, the scientist protagonist with the glasses, were ludicrous: e.g., “The fire will spread this poison until the entire continent is dead” – nothing could be further from the truth. The majority of dangerous core radioactivity (that could provide high dose rates) would have been released in the first week (e.g. I-131 has a half-life of 8 days and most of would have been released in the first day). The fire burned for 10 days, so most of the damage that could have happened, did in fact happen. Continued burning could have released more the solid waste (fuel actinides and solid fission products) but these particles have lower dose rates and do not travel as far from the site as gasses and volatiles. None of <50 potentially radiation related deaths recorded through 2006 were likely influenced by the release of solid radionuclides. So, even though only 3.5% of the solid radioactivity was released, and burning the rest of the radionuclides out of the core would not have had much effect either (except for increasing the size and/or time limits of post-accident exclusion zones); i.e., even it if the fire burned long enough to release it all, the vast majority of damage would have remained to be the short-lived gases and volatiles. Also note that the 30-km Chenobyl evacuation zone was actually scientifically conservative, and the protagonist was once again wrong when he yelled at the boss declaring that it was a stupid uninformed decision made by party officials.
Another dumb quote from the protagonist was “If we fly over the reactor core we’ll be dead within a week”. In reality, even if they hovered over the reactor for a minute, the dose rate at that elevation (above adjacent roof height) would not have provided acute health risk. If they left the windows open at hovered within the plume without a mask for several minutes maybe, but for the most part the flying-over scenario (even just 12 hours after the explosion) would have been less dose than workers that spent 90 seconds outside on the roof – which delivered a benign occupational-limit level of dose. Then, after this highly exaggerated warning about the human risk of flying over the fire, HBO outdid itself. It implied that radiation caused the blades on a helicopter to break apart – I am actually glad they put that in, because you’ve got to hope that most people would know this scene was asinine, and hopefully then question some of the other claims.
The insinuation of the miner scenes (recruitment and on-site) make it seem like they were going on suicide missions, which of course they weren’t. The on-site trailer meeting starts with the protagonist telling the boss that he’s not good a lying, implying that the “lie” would be to tell the miners that they don’t face grave danger. The boss tells him that lying to miners is a bad idea, so instead he doesn’t “lie”. The miner crew chief (my favorite character) asks about the mask and the protagonist’s response implies that it won’t make much difference in the big picture, giving the vibe that you guys are doomed. In reality, their situation was not overly dangerous (maybe their usual risk of cave collapse or toxic inhalation, but not from radiation, especially if they wore a mask), because breathing in radionuclides was their only significant radiation risk. Still, HBO states "It is estimated that at least 100 of them died before the age of 40", but there doesn't appear to be any basis for this statement Even with no mask, and no clothes, it is unlikely that any of the 400 miners experienced serious health effects from radiation, because their doses would have been orders of magnitude lower than the first responders.
The Pregnant Mother:
The most egregious story was that of the pregnant mother. They go at length to emphasize how important it is that she keep her distance, which grossly misrepresents that nature of radiation. The damage done to the workers who approached the core was both internal (cellular) damage caused by ionizing radiation from the exposed reactor core, and external damage to the lungs/skin caused by alpha/beta emissions from radioactive particles. After that point, it is almost certain that all victims were showered and cleaned to remove contamination, so there was subsequently no threat. So back to the pregnant mother. Her husband was likely burned very badly and had grave radiation damage, but he posed no threat to his wife (actually, much lower than if she was home back in Pripyat). My heart sank when the apparently technical credible character (the women scientist from Belarus) reaffirmed this gross technical error, when she by yelled at the nurse for not preventing the mother from getting too close. The craziest claim was that the baby absorbed the radiation and saved the mother. If anything it would be the opposite, the mother’s body would slightly shield the baby from ionizing radiation (i.e. the baby is inside the mother) and from the radioactive particles that came in contact with the mothers skin and lungs. Some radioactivity would enter the bloodstream, but even then, the placenta should have kept the concentration of absorbed contaminants lower in the baby’s blood than the mothers (the only truth would be that the fetus would be more susceptible to radiation damage).
Bridge of Death:
Initially, I didn’t mind the bridge scene because they were slightly increasing their chance of cancer, if they were indeed standing outdoors under the plume, because of the increased chance of inhaling highly-radioactive particles -- dangerous for the young kids, especially only a few hours after the explosion. The only statistically significant deaths from Chernobyl radiation, other than first responders, were children that developed thyroid cancer by ingesting radioactive iodine (note: the purpose of taking iodine pills is the saturate the thyroid with “good” iodine so that less radioactive iodine is absorbed). As expected, the number of thyroid cancers increased significantly for the population surrounding Chernobyl, mostly children: 9 of these patients died, many likely due to the radiation. So back to the bridge of death – at the end HBO implied that most of them had died via radiation "Of the people who watched from the railway bridge, it has been reported that none of the survived", but there is no evidence of this, and given the actual scientific facts it is extremely unlikely that any of them did (unless some of the 9 children that died were on that bridge).
The Scientific Consensus:
There were 134 documented emergency first responders with high exposure: 29 first responders died within months from Acute Radiation Sickness (ARS). There were 19 fatalities among this group over the next 20 years, but that was within the expected morbidity range (so no significant radiation effect). None of the 3 “suicide” squad guys sent to open the valves under the reactor died from radiation: 1 died from heart attack and the other 2 are alive today. The troops sent to clear off the roof got doses within the traditional standards for rad workers, which has not been shown to increase cancer risk. There has been no demonstrated statistical increase in cancer mortality with the public in surrounding areas (except for the aforementioned 9 deaths), which is remarkable because so many people have been looking hard find a correlation for decades (usually when people are looking for some sort of statistical anomaly they will find it). From the comprehensive 2006 World Health Organization (WHO) report – “The recent morbidity and mortality studies of both emergency workers and populations of areas contaminated with radionuclides in Belarus, Russia and Ukraine do not contradict pre-Chernobyl scientific data and models”; i.e. no statistical evidence of increase deaths that could be caused by radiation.
Over-Predicted Future Cancer Deaths:
HBO declares "most estimates range from 4,000 to 93,000 deaths", but the scientific data thus far completely debunks this, and the final tally will probably be <100. The low end of the HBO range, 4,000 deaths, was indeed in the range of the "scientific" estimations made in 1986, some of which were included in the 2006 WHO report (only for reference, i.e. they were not endorsed by the WHO). The "scientific" prediction of several thousands dead used the Linear No-Threshold (LNT) model, which is increasingly being identified as incorrect at low dose rates. The LNT model is mostly based on Japanese A-bomb high-dose survivors, which as previously mentioned is apples and oranges. The more-recent scientific data clearly disputes the validity of the LNT model at low dose rates; i.e. these studies have investigated low additional doses (within the annual natural background) have found no negative impacts. Many will actually argue that low doses are beneficial (look up hormesis), but either way the effects are minimal. The cancer predictions displayed in the 2006 WHO report have thus far grossly exceeded what has actually happened for the first 30 years. The same prediction methodology that projected the thousands of eventual deaths, also predicted a 375% increase in cancer+leukemia deaths among the liquidators in the first 10 years (190 deaths versus 40) – this should have been clearly visible in the statistics of this controlled dataset, yet no increase was found. The latency period of solid cancer is decades, so it can still be speculated that a spike will eventually appear, but 30 +years after the accident no increase (certainly not thousands) has been scientifically demonstrated.
Fear of Radiation is Worse than Radiation Itself:
As horrific as ~50 deaths are, there are thousands of manmade, industrial accidents that have caused more fatalities (google it for yourself). In addition, nuclear is proven to be far safer (fewer deaths per energy generated) than any other energy source (cold, oil, natural gas, biofuel, wind, hydro, solar - you can google this too). Why a miniseries? because fear of radiation sells. Tell that to the victims of Fukishima; the tsunami killed thousands, but coverage by the media focused on the reactor and radiation harmed no one (except for some casualties caused by the evacuation due to dear of radiation). The same affect is evident in the regions surrounding Chernobyl: coverage by the media convinced people their bodies were ticking cancer time bombs and fear of radiation made them leave their homes, with extreme detrimental sociological effects (depression, suicides and abortions). Again from the 2006 WHO report “Consensus: The mental health impact of Chernobyl is the largest public health problem caused by the accident to date”; so even for the worst nuclear accident of all time, fear of radiation was worse than the radiation itself. Now, HBO has created a show that spreads the irrational fear of radiation to new extremes (I wish the actors that played the scientists weren't so good!) – their highly successful show has misinformed 10s of millions. This fear of radiation is holding back humanity, because public/political opposition and the corresponding inflated cost (over regulation) has strongly curtailed the use of nuclear energy.