The Chernobyl accident was a nuclear explosion which took place at the Chernobyl nuclear power plant in the city of Pripyat during the time of the Ukrainian Soviet Socialist Republic of the Soviet Union (USSR).
The Chernobyl incident is one of only two nuclear disasters classified as a level 7 event (the maximum classification) on the International Nuclear Event Scale, the other being the Fukushima Daiichi nuclear disaster in Japan in 2011. The struggle to contain the contamination and avert a greater catastrophe ultimately involved over 500,000 workers and cost an estimated US$235 billion over the past thirty years. Thirty one people died during the accident itself, and there are long-term effects on survivors being investigated to this day.
During an experiment scheduled to test a potential safety emergency core cooling feature, one of the reactors suffered a catastrophic power increase, leading to explosions in its core. These explosions dispersed large quantities of radioactive fuel and core materials into the atmosphere and ignited the combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles carried by the smoke, as the reactor was not double contained.
When did the Chernobyl Disaster Happen?
On 26 April 1986, during a systems test, there was an unexpected power surge that began a series of accidents; leading to explosions, a fire, and ultimately releasing radioactive particles into the air. The deadly particles spread all over a huge area in Europe. Large areas were evacuated and the city of Pripyat, near the accident site, still remains a ghost town today.
In Brief: What Caused the Chernobyl Nuclear Disaster?
According to the International Atomic Energy Agency’s (IAEA) 1986 analysis, the main cause of the accident was an operators’ actions. However, according to the IAEA’s 1993 revised analysis the main cause was the reactor design. Much of the primary data covering the disaster, as registered by the instruments and sensors, was not completely published in the official sources.
Human factors are considered to be a major element in causing the accident. The International Nuclear Safety Group (INSAG) reported that both the operating regulations and staff handled the disabling of the reactor protection correctly, but the operating crew’s deviation from the test program was mostly to blame for the failure. INSAG called attention to the inadequate “culture of safety” at all levels.
The poor quality of engineering, design, operating procedures and instructions, and their conflicting character, put a heavy burden on the operating crew, including the chief engineer. “The accident can be said to have flowed from a deficient safety culture, not only at the Chernobyl plant, but throughout the Soviet design, operating and regulatory organizations for nuclear power that existed at that time.”
Since the Chernobyl disaster, IAEA has strived to improve safety culture around the globe and ensure safety measures are in place and clearly communicated from the design stages onward.
In Detail: What led to the explosion at Chernobyl?
Is there a single thing that can be pointed to and declared – that’s it, that was the problem…
Probably not, as, like all accidents, there are multiple factors that confluence in order to bring it about.
Chernobyl was a massive event, with many hundreds of thousands of man-hours devoted to either finding guilt, apportioning blame or actually finding out what went wrong.
This article can’t even begin to scratch the surface of this cataclysmic event – it’s just intended to keep the memory alive…
You could point to the original design being flawed, or to the culture of secrecy and blind obedience, to the lack of adequate safety measures, or a host of other things, but none of them really tell you why, in the early morning of April the 26th 1986, the number 4 reactor of the Chernobyl nuclear power plant experienced a catastrophic event that led to the worlds’ worst release of radioactive poisons.
But, as we have to start somewhere, let’s start in Iraq…
How Osirak and Operation Opera led to Chernobyl
The French Osirak nuclear reactor was about to come on line. Osirak was a nickname given to it by the French supplier, a combination of the Osiris reactor class name and Iraq. Called the Tammuz 1 by the Iraqis, Saddam Hussain had acquired it with a view to pursuing his long held dream of a nuclear arsenal, but the State of Israel had its own views on that…
The single commonly held view between otherwise fervent enemies, Iraq and Iran, (and other middle eastern States), was the destruction of Israel by any achievable means.
The introduction of a possible nuclear capability into this hostility was simply unacceptable for the Israeli government of the day.
In actual fact, the reactor was specifically designed so as not to generate weapons grade nuclear isotopes, or at least to only do so in a painfully slow manner, but this fact was unknown to the Israelis, and it is doubtful that it would have stopped them, as without sufficient independent controls, fuel loads can be shuffled around and greater neutron flux achieved in order to attain greater weapons grade isotope production.
The problem for the Israelis was that you can’t just go and drop a bomb on a nuclear reactor. Not only is it a hardened target, with an extremely strong containment dome,
it’s also considered to be very poor form by the international community to release enormous amounts of radioactive material into the atmosphere, and poison innocent neighbouring States. To do so would have resulted in the State of Israel becoming an international pariah.
But, as it was one of the stated intentions of the then Iraqi regime to wipe the State of Israel off the map, it was also completely untenable for Israel to watch Iraq acquire a nuclear facility, so they felt they had to act, and act quickly. To this end, Operation Opera was launched, and before the reactor became fully operational, the Israelis bombed the ancillary components of the reactor – the external cooling and power supply systems.
Nuclear reactors not only generate electricity, they also consume it, and in large amounts.
Without the supply of coolant and electricity, the plant was rendered useless.
The cold war was very much in force when this occurred, and the destruction of this reactor made the Soviet government of the day very nervous – could this happen to their reactors, as a result of a hostile air raid? To this end, they instituted a system check at all their nuclear facilities, designed to test that the steam generation of the reactor was sufficient to continue to power the primary coolant water pumps and control rods until the emergency diesel generators could power up and come on line, taking over the role.
These checks were designed to take place prior to each reactor entering service, but this didn’t happen at Chernobyl…
In this article, we’ll look at what did happen at Chernobyl, why it happened, how it could possibly happen, and why it’s still happening, even today.
But first, back to basics…
Nuclear reactor: The Point of Criticality
A conventional nuclear reactor is essentially a large kettle. It heats up water to create steam, and this steam pushes its way through turbines that drive generators which produce electricity. To heat the water, it makes use of radioactive material, in the form of cylindrical fuel rods.
These rods are composed of various elements (including different combinations of elements within different parts of the reactor), but essentially, they are all primarily comprised of Uranium. Uranium is a radioactive material – but what does this actually mean?
For the purposes of this article, it means a material that decays, emitting neutrons as it does so. Quite a few materials do this, but only the very heavy elements of the periodic table do so in a manner that is both useful for energy production, and only Uranium is available in commercial quantities that warrant its extraction from the ore that it resides in for use in a nuclear power plant.
So, when you’ve managed to get the pure Uranium out of the ore, and then concentrated it, (an eye wateringly expensive process), this means that there are more and more neutrons being discharged from it – this is usually in the form of Alpha radiation (the human skin will essentially stop harmful effects of this).
But not all of the discharge is external – neutrons are being discharged internally as well, by all the atoms that aren’t on the surface of the material. And the more nuclear material you have, the more neutrons there are flying around inside the mass of the material, hoping to have a massive argument. (This is very dependent upon the shape of the material, the sphere being the worst (in terms of critical mass, and the cylindrical rod being the most stable).
When a neutron collides with a Uranium 235 nucleus, several things happen, but the important thing to note here is that 3 free neutrons are released each time such a collision occurs.
Neutrons are emitted many times a second by any given mass of Uranium, (approximately 3×10^4 n/s-g for U235) as it undergoes its natural decay process, but they generally tend to bounce off things, bump against each other and not really make any difference – they just disappear into the atmosphere and contribute to the background radiation level.
But, if you get enough of them together, in the right place and at the right time, all hell breaks loose… basic atomic weapons make use of this by conjoining enough nuclear material together and reaching a point known as criticality – this occurs when the mass of the material is sufficient to sustain a chain reaction.
This means that enough stray Neutrons are emitted from the mass of the material so that there are sufficient collisions to ensure that every time a Neutron collides with a Uranium nucleus, it is guaranteed that another set of collisions will occur that generate enough stray Neutrons to ensure further collisions.
Natural Uranium simply doesn’t have enough concentrated atoms to ensure that this can be achieved – the Uranium has to be concentrated, so that the density of the Uranium nuclei is such that the Neutrons (in essence) can’t find a gap through them.
That process, in itself, isn’t sufficient to produce a nuclear detonation, but it is sufficient to produce both intense radiation and crucially, thermal energy.
This is the point of criticality.
Entropy is real, and it means that everything we know about, touch and interact with simply wishes to be left alone. All materials exhibit a rate of decay, whether it be Iron rusting, or Uranium emitting Neutrons. Radioactive materials also actively exhibit the property of maximum entropy.
To accurately describe this would require an article all on it’s own, so for the purposes of this article, would you mind accepting the very useful lie that everything in the world is in a ‘raised’ state and wants to do nothing more than revert back to primordial slime, and a state of neutrality, with no more energy to be either given or taken?
Expressed differently, you can take two lumps of Uranium that have a sub-critical mass and push them into contact with each other – the result is intense radiation. Separate them, and the neutron flux diminishes immediately.
This is also known as a ‘Chain Reaction’
The problem for nuclear reactions is fundamentally that Neutrons don’t really want to collide with ‘anything’ – they keep on missing and missing ‘things’, all the time…
So, slow Neutrons are good. Well, if you want a big bang… but they’re also good for the big kettle too…
It’s basic probability theory really – if you’ve got lots and lots of different bits whizzing around at a really high speed, then the incidental chance of them colliding is an exponent of each components relative velocity – think of driving an open top car through a rain shower. The faster you drive, the less wet you will get.
In the case of a nuclear reactor, we want to get wet – so we need to slow the Neutrons down, and make them collide with Uranium atoms more efficiently.
To do this, a moderator is made use of – A moderator is a material that slows down ‘Fast’ Neutrons, but doesn’t absorb them (or accept them into their atomic structure). They are typically reduced from a velocity of 10% of light speed, to a velocity of about a few kilometres per second. (This gets very complicated, very, very quickly, and doesn’t really fall into the ambit of this simple article. So suffice it to say, no Neutrons = no Reactor).
The essential issue is really about how you effectively control these little sods.
In most reactors, the moderator is simply water. In Chernobyl, it was solid Graphite blocks with water channels. This plays a major part in what transpires in the accident.
Slower Neutrons equals more collisions, which equals more thermal output from the reactor. This simply means that it generates more steam per given volume of water flow through the reactor.
In essence, a nuclear reactor is a very, very slow, and controlled nuclear bomb.
This statement does not in any way speak to the issues of nuclear power and the challenges it presents – it simply means what it says . A slow, controlled release of thermal fission energy, with the energy released being constantly thermally channelled away into the production of steam and then further converted into mechanical and then electrical energy.
But even in the worst case scenario, it’s only a potential bomb that could go pop, as opposed to bang (although there are alternate theories to this statement).¹
In Chernobyl, it did go pop. But it was the most devastating pop the world has ever experienced, and continues to experience… The ‘Pop’ occurred not from a nuclear reaction in itself, but as the result of nuclear reactions running out of control, resulting in a massive hydrothermal shock to the reactor, which led to its destruction.
Never underestimate the power of steam.
¹The Chernobyl Reactor: Design Features and Reasons for Accident
Mikhail V. MALKO, Joint Institute of Power and Nuclear Research, National Academy of Sciences of Belarus. Krasin Str.99, Minsk, Sosny, 220109, Republic of Belarus: [email protected]
The Soviet culture was one of the main players in the disaster
In the Soviet era, although diminishing in 1986, the following held true: The boss was the boss. It was as simple as that. The phrases ‘Trade Union” and ‘Soviet Union’ were mutually exclusive. He, (and it was always ‘He’) held the power to fire any individual at the stroke of his pen, and held the livelihood of many hundreds of workers at his behest.
This was especially true in the dormitory town of Pripyat – a town specifically constructed to allow workers at the massive Chernobyl site to live close to their source of employment. By Soviet standards of the day, this was the equivalent of living, say, on the French Riviera. The shops even had food and goods in them. Something that was almost unheard of in most of Russia at the time, at least not without having to queue for an hour or two…
So if you were one of the reactor operators, settled there, with your family – what would you do when a far senior person gave you a command to perform that you didn’t think would be safe to execute? Would you comply, or stand up to him, knowing that your next posting would be in some godforsaken hole in Siberia… And besides, Soviet reactors were bullet proof.
Every Soviet reactor operator knew that – they had never had a single reactor incident, as they were all perfectly designed. Some people, of course, knew that wasn’t true. But those people also had bosses…
The Chernobyl RBMK 1000 reactor design
The Chernobyl RBMK 1000 reactor design was one of several prevalent nuclear reactor types operating in the Soviet Union at the time.
The literal translation of the Russian RBMK acronym is ‘high pressure channel type’, and the number ‘1000’ relates to the thermal output of the reactor, in Megawatts. There were also RBMK 1500 models. Same design, but different scales.
In each case, the electrical output was approximately 1/3 of the thermal output of the reactors, resulting in a quite inefficient design. But they also served the dual purpose of producing Plutonium for nuclear weapons and they didn’t require homogeneously welded containment vessels that high pressure water reactor designs require – this is considered by multiple sources to be beyond the production capabilities of the day for the then Soviet Union.
So they were cheap (in nuclear terms), and simple and serviceable through local personnel – a fundamental requirement of the then Soviet Government.
The RBMK series were essentially two reactors in one, having two independent feed water and pump systems to cycle water into the fuel elements of the actual reactor core.
With the wonderful facility of hindsight, it can be easily argued that multiple sub systems and elements simply add complexity (and therefore different failure modes) to an already exceptionally complex system. This may or may not be true – but it is also equally relevant to understand the risk adverse philosophy of the engineers and physicists who designed the things.
They weren’t idiots. There is sometimes a Western culture of mocking Soviet era technology, but if you take a good step back and consider what they achieved with what they had available to them at the time, the one word that springs to my mind is ‘Robust’.
That’s not to say that mistakes weren’t made – they certainly were.
With a dearth of materials and process technology, they applied what they had available in the most efficient manner (the scientists and engineers), but they were ultimately stymied by the overarching culture that was prevalent in that era. Fear.
That culture of fear led to a host of shortcomings that manifested itself in a multiplicity of ways, from deadlines to short cuts and a simple lack of the required materials.
The Chernobyl accident didn’t happen just because Anatoly Dyatlov, the Deputy Chief Engineer said, “OK, switch everything off, and lets see what happens….” but having said that, he was unbelievably arrogant and reckless in his handling of the test, and to his dying day, refused to take any responsibility for the accident.
The amount of safety systems that had to be bypassed and/or physically disabled includes, but is not limited to, the following:
- Emergency Core Cooling System disabled
- Automatic control rod system disabled
- Manual extraction of almost all control rods
- Steam/water separator alarms repeatedly cancelled
- Feed water flow rate alarms repeatedly cancelled
- Excess steam alarms repeatedly cancelled
- Neutron power alarms repeatedly cancelled
- Emergency thermal-hydraulic parameter alarms repeatedly cancelled
- Two feed water circulation pumps switched off
- Turbine emergency regulating valves disabled
If you actually intended to weaponise a nuclear reactor, you couldn’t have done a better job….
Chernobyl: The event
The test is very well documented – in essence, it assumed a lack of power to the feed water pumps that continually circulate water through the reactor.
If this happened, there were emergency back up generators that would kick in to provide power to the pumps in order to keep the vital flow of water through the reactor.
The problem was that these generators took between 10/15 seconds to kick in, and a further 50 seconds to reach a power level that was sufficient to drive the pumps.
So perhaps the reactor could cool itself for this short period of time?
Even in a total shut down event, this type of reactor would still have about 7% of it’s thermal energy available to its operators, as a steam product. Could this steam be used to drive the pumps for about a minute?
Obviously, there would be hysteresis in the system, but would this be insignificant enough to enable that approximate 1 minute gap to be bridged…?
Every single reactor ever built is unique in its operating properties, power output and individual ‘proclivities’. In short, they’re twitchy, moody little bastards that are extremely stable until prodded with a stick, and on the morning of April 26th, Anatoly Dyatlov wielded a very big stick indeed…
In the case of Chernobyl, the specific rot set in when the No. 4 reactor changed over to the night shift. Reactor 4 was scheduled for a routine maintenance shut down (and test) that morning, and would have been in a stable state, except that the Kiev regional electricity grid controller requested that it remain online in order to supplant supply from other off-line power plants.
In order to run the test, the reactor was required to operate at a minimum output of 700Mw – as this was lower than normal capacity, the reactor had to be cooled (slowed down) prior to the commencement of the test.
The initiation of the slowing down of the neutron flux in the reactor is where the accident, if you really want to isolate it to the pure technical elements, started…
The mix of radionuclides within the reactor core meant that a condition known as reactor poisoning could occur. And, as it could, it did.
One of the radioactive by-products of the reactor is Xenon 135. This is a Neutron absorber.
It’s usually converted into the stable isotope of Xenon 136 via the decay of Iodine 135.
But when the power down occurred, mistakes were made with regard to control rod insertion and position, and this led to a slowing down of the neutron flux to such an extent that the reactor spiralled into a almost ‘cold state’ due to the excess of Xenon 135.
So it was bubbling away at about 30Mw. In this condition, it was almost impossible for the operators to control the steam pressure between the two separate diaurators (steam separator drums).
Think of a playground see saw, but with a big drum of water on each end, and with two inlet pipes, outlet pipes and a connecting pipe. If you slowly move water between them, the see saw will slowly move in the vector of the heavier drum. So you have to divert the flow of water into the other drum to counterbalance this. But it takes time, and the see saw rocks more as the inertia of the system is slower…
With a high pressure system, there’s more room for volatility, but far more room (in terms of time) to take corrective action, and thus decrease the see saw effect. Thus operating stability is more easily maintained. So, for Chernobyl, high pressure was a good thing.
In its operating condition of 30Mw (thermal) it was impossible to run the test, so the reactor operators were ordered to rapidly increase the power output. To do this within the time available to them in their shift (the last one before maintenance shutdown), they figuratively, and almost literally, pulled out all the stops – the ‘stops’ being the neutron absorbing control rods.
Below is an image of the condition of the reactor at the time of the event, courtesy of Wikipedia.
The important blocks are the Green ones – these are the upper control rods that primarily governed the neutron flux. The number associated with each one is the depth to which it was inserted into the reactor. You’ll see a lot of zeros in the image…
The Red elements are automatic control rods, whilst the Yellow are the minor bottom rods and the Blue are neutron sources (fuel rods).
The RBMK reactors are extremely tall (or deep) constructions, and one of the main problems was that the operators simply didn’t know what was happening near the bottom of the reactor. Sensors only have a limited value in such situations, as they themselves are prone to neutron embrittlement and Gamma radiation.
To further complicate matters, the RBMK reactor series suffered from a condition known as a ‘positive steam void co-efficient’.
Most Western reactors have the reverse of this – a negative steam void co-efficient. This means that when the amount of steam in the reactor increases, the neutron flux diminishes, and therefore the reactivity diminishes.
A positive steam void co-efficient is very succinctly described by the World Nuclear Association, quoted below;
Reactors cooled by boiling water will contain a certain amount of steam in the core. Because water is both a more efficient coolant and a more effective neutron absorber than steam, a change in the proportion of steam bubbles, or ‘voids’, in the coolant will result in a change in core reactivity. The ratio of these changes is termed the void coefficient of reactivity. When the void coefficient is negative, an increase in steam will lead to a decrease in reactivity.
In those reactors where the same water circuit acts as both moderator and coolant, excess steam generation reduces the slowing of neutrons necessary to sustain the nuclear chain reaction. This leads to a reduction in power, and is a basic safety feature of most Western reactors.
In reactor designs where the moderator and coolant are of different materials, excess steam reduces the cooling of the reactor, but as the moderator remains intact the nuclear chain reaction continues. In some of these reactors, most notably the RBMK, the neutron absorbing properties of the cooling water are a significant factor in the operating characteristics. In such cases, the reduction in neutron absorbtion as a result of steam production, and the consequent presence of extra free neutrons, enhances the chain reaction. This leads to an increase in the reactivity of the system.
Operating reactivity margin
The Chernobyl operators really weren’t well appraised as to the specific reactivity margin required for safe operation of the reactor – the basic explanation for this is that for any given state of operational power, an equivalent amount of neutron absorbing rods should be inserted within the core of the reactor, to achieve a balance.
Again, the World Nuclear Association is quoted below;
Although the definition is not precise, the operating reactivity margin (ORM) is essentially the number of ‘equivalent’ control rods of nominal worth remaining in the reactor core. The operators at Chernobyl seemed to believe that safety criteria would be met so long as the lower limit for the ORM of 15 equivalent rods was adhered to, regardless of the actual configuration of the core. The operators were not aware of the ‘positive scram’ effect where, following a scram signal, the initial entry of the control rods actually added reactivity to the lower region of the core.
The ORM could have an extreme effect on the void coefficient of reactivity, as was the case for the core configuration of Chernobyl 4 in the run-up to the accident. Unacceptably large void coefficients were prevented for initial cores by increasing fuel enrichment levels, with the excess reactivity balanced by fixed absorbers. However, with increasing fuel burn-up, these absorbers could be removed to maintain the fuel irradiation levels – shifting the void coefficient in the positive direction and increasing the sensitivity of the coefficient to the extent of insertion of the control and protection rods.
At 01:21, on the morning of the 26th of April, 1986, the reactor was in a state of almost cold shutdown, through many mistakes and arrogant decisions.
I’ve made a concious point of not naming the relevant reactor operators, as I personally believe that they have been vilified enough through the then existing Soviet legal system.
These were people who simply wished to perform their duties to the best of their abilities whilst keeping a roof over their families head.
Suffice it to say, any concerns they raised were shot down in flames by Dyatlov.
At 01:22, they cocked the hammer, by removing almost all of the control rods from the reactor core. Due to their lack of knowledge about the aforementioned steam void coefficient and Operating Reactivity Margin, the reactor power spiked considerably.
At 01.23, in a state of panic, they pulled the trigger, by pressing the emergency AZ 5 scram button. This re-inserted all of the control rods (simultaneously) into the bowels of the Chernobyl No.4 reactor.
Two things happened almost immediately – the water in those control rod channels was displaced by the rod insertion. Remember, these are very deep reactors, so the rods had to travel over ten meters, at a speed of about 0.4m/s. That’s a skeletal rate of descent in nuclear reactor terms.
For this type of reactor, less water means more reactions. So the Neutron flux spiked… To top that off, the rods themselves had an initial 4.5 meters of Graphite (a Neutron moderator) at their tips. This has been termed the ‘End rods condition’.
So, the water was removed, and the Graphite was added.
It’s estimated that the reactor reached approximately 100 times it’s intended power in the following seconds. It’s widely documented that there were two explosions, within seconds of each other. The first is believed to be the rupturing of localised fuel channels at the base of the reactor that simply burst from intense heat, and that the second (major) steam explosion was as a result of the buckled channels preventing the full insertion of the control rods.
In any event, the second explosion dislodged the 1000 ton steel roof of the reactor, with most sources indicating that it fell back approximately where it was positioned – but the lid was no longer on the kettle…
In the immediate aftermath of the explosion, there was an initial feeling of disbelief, followed quickly by denial. Such is the human condition in all such catastrophic events. In this instance, it was further overshadowed by the culture of blame…
When the Chernobyl number 4 reactor blew itself to smithereens, the operators were immediately ordered to flood water into the reactor (which simply didn’t exist any more).
Following the realisation that this could be a world changing event, the senior management at the plant ordered radiation surveys to be undertaken. These were duly carried out by people whose lives would be severely curtailed through radiation poisoning.
But the news was good – Only 3.5 Roentgens per hour.. (A Roentgen is a now defunct measure of radiation based on the absorption of X rays over time into the body) and although that would exceed your monthly permissible (Western culture) dosage within a few minutes, it could have been an awful lot worse.
There was a tiny little problem – the radiation meters only went up to 3.5 Roentgens.
The real count was between 1000/1500 Roentgens per hour around what remained of the reactor, but, hey – why bother the Communist Party leadership with the truth that will get you thrown in prison (at best), when you can offer a relative olive branch of 3.5?
Only three days later were the many thousand occupants of Pripyat (the dormitory town that the workers of Chernobyl lived in) instructed to ‘temporarily’ leave their homes. There is well documented footage of the exodus being filmed through old film reel cameras, with the radiation showing up on the film as white flashes and streaks.
Needless to say, Pripyat is now a permanent ‘ghost town’.
For the people intimately involved in the accident, in the immediate aftermath, there was a mobilisation of people unlike the modern world has ever seen, except in time of war.
More than 800,000 people were involved in the clean up of Chernobyl, and they were exposed to truly horrible conditions.
Following the accident, the hole blown in the roof and walls of Chernobyl No. 4 reactor was releasing more radioactivity per day than every single nuclear accident in the world, combined. Every day…
The Soviet scientists weren’t daft – they were the opposite. Some of the most talented nuclear engineers on the planet, they realised that they faced an unprecedented challenge.
In order to mitigate this disaster, what do you do? Drop blocks of Lead into the reactor? No…
A single 20 Kg block of Lead (of which hundreds of thousands would be required) dropped from 300 Meters will achieve a kinetic energy of almost 900,000 Joules and potentially smash through the base of the reactor floor, leading to an even worst disaster, one that will be covered shortly…
The eventual temporary fix was a mix of Boron (an extremely efficient neutron absorber) and sand.
They did use Lead though, to protect themselves – below is an image of a helicopter seat covered with Lead to protect the pilot..
The radiation was so intense that every single robot commissioned to remove the hideously contaminated Graphite block fragments from what remained of the roof of Unit 4 either simply stopped working or committed vehicular suicide by driving itself off the roof…
The Ionizing radiation was simply too much for sensitive, microscopic scale, circuit boards. So the Soviet Union decided to deploy ‘Bio-robots’ to remove the stuff from the roof. Yes, you read that correctly.
Approximately 200,000 of them, mostly from the military.
There has been much discussion about avarice in the face of the remuneration they received for their efforts, given the danger pay financial benefits.
But the fact remains that 2 minutes was the maximum single individual exposure time, and everyone involved on the roof dispersal operation reported tingling lips, aching joints and blurred, scraping vision immediately post their exposure.
Below is an image of the ‘Bio-robots’ throwing unbelievably radioactive Graphite lumps off the remains of the No. 4 reactor. The white streaks at the bottom of the picture are due to the intense radiation infiltrating the negative of the exposed image.
The workers involved in this effort actually fashioned a form of underwear, made of Lead, and although not clear in the above image, they also made use of Lead waistcoats underneath their outer garb.
The average radiation dose they received was the equivalent of 1000 chest X rays.
In two minutes…
Radiation dosage to the human body has been subject to quite a few different metrics over the past 70 years, and includes Becquerels, Roentgens, Milli-Sieverts and a few other besides, but the simple fact is that it fundamentally isn’t good.
Current theory states that it doesn’t matter when you get exposed, or over what time frame – You have a certain resilience to radiation, and when you exceed that, bad luck.
We’re back to basic probability theory here – your bodily atoms have (X) chance of getting mutated if they are exposed to (X) amount of radiation. As a species, we’re generally conservative – speak to anyone in Brazil – they exist quite happily with over twice the background count for Europe.
But for the people at Chernobyl, that was nothing but intellectual twaddle. This amount will kill you, and if treated as a poison (which it technically is), the radiation dosage placed all of the control room workers of the plant in hospital, and resulted in the deaths of approx. ¾ of them within 3 weeks.
For the people of Pripyat, the majority of them were evacuated to the city of Kiev and other urban areas. They were told that they would be able to re-occupy their homes in relatively short order.
This, of course, didn’t happen.
Pripyat remains a horribly radioactively contaminated ghost town, and will remain so through our, and many other generations lifetimes.
It’s very easy to consign such an accident to history, but the fact is that it happened yesterday in terms of our technological development as a species.
In the relative blink of an eye, humankind was granted access to an almost unlimited energy source.
The child in the image knows the consequences of our desire for more energy – he was born in Ukraine, just at the wrong time…
The initial Soviet response to the accident (at the reactor) was jaw droppingly awesome – it’s probable that no other nation on earth could have put together such a combined effort to such a disaster in the same way.
I’m certainly no fan of the then communist regime, but that doesn’t automatically preclude the individuals that helped to prevent the further spread of radioactivity.
They got rewarded of course, with medals…
A bit of Tin for a few years of your life doesn’t seem like a fair trade to me….
But if you went to Kiev (or were evacuated there), and were lucky enough to receive one of these – a green-coloured ticket to the May day celebrations of that year…
Then you would be celebrating without the presence of any Communist party official or family member – they all skulked off three days prior to the event, having been informed about the impending radiation cloud heading their way…
Meanwhile, back at the reactor, things were only getting worse.
Owing to the immense amount of water that had been poured into the devastated remains of reactor No. 4, both by the reactor operators and subsequent fire suppression attempts, there was a sub basement level machinery space directly below the remains of the reactor and its molten core, and that large space was now full of water…
When, not if, the molten remains of the reactor fuel burned through the Concrete and into that space, the resultant hydro-thermal explosion would be enormous, which, source dependant, would have resulted in an explosion equivalent to between 3 to 5 megatons worth of residual radiation products over a huge distance. That equates to most of Europe becoming uninhabitable for hundreds of years.
And below that machinery space lay a giant aquifer, one that supplies many hundreds of thousands of people with their daily drinking water.
In a truly remarkable event, the officials involved asked for scuba diver volunteers to enter the machinery room and open various valves in order to release the water. This was a suicide mission, given the intense radioactivity of the water.
They got three volunteers, and it would be disgraceful not to mention them by name here. They were; Alexei Ananenko, Valeri Bezpalov and Boris Baranov.
Mr. Ananenko was the only person on shift duty at the time of the request who knew the actual location of the valve, and was assisted by the other two volunteers.
Their actions resulted in the draining of over 5 million Gallons of water over the forthcoming days, and they saved millions of lives as a direct result of their bravery.
To the best knowledge of the author, amazingly, and despite contradictory reports, all three survived the direct results of this encounter with extreme radioactivity, with one of them passing away a few years ago, and the others still being alive.
They are all owed a huge debt of gratitude by, at the very least, every European who was alive at that time. They didn’t design the reactor, they didn’t have any say in how it operated – they simply did what they knew was best for humankind.
The scale of the accident was unprecedented – many sources have placed the amount of total radioactivity released in the region of 3 to 9 billion curies of radioactive matter. This becomes a sum where the numbers rapidly become incomprehensible. A single curie is the equivalent of 37 billion becquerels per second (the SI equivalent of the curie).
The problem is, there are measurement units to describe the power of the emission source, different units to describe the absorption into organic material and yet still different units to describe the probable biological damage done to cell structure upon radiation absorption. To tie all these together into meaningful statistics becomes both impossible and irrelevant – only the end result provides the meaningful answer.
This is further complicated by the combined use of both S.I. and non standard units.
So the simple fact is that an awful lot of radiation was emitted by Chernobyl. A really, really vast amount. The EURT (East Urals Radioactive Trace), pales into insignificance by comparison. This was a radioactive release from the Mayak Plutonium plant, close to Kyshtym.
Many radioactive particles were released from an accident that never happened in 1957.
Chernobyl has resulted in a large exclusion zone and a continuing maintenance of the site, at vast cost. Recently, the new containment dome has been slid into place to cover the now crumbling original sarcophagus that covered the smoking remains of the reactor (in and of itself, a remarkable feat of engineering and human endurance).
This houses ‘the elephant’s foot’ – a nickname given to the molten remains of the core. This actually gave birth to a new element, known as ‘Corium’. This photo was taken via a remote robot controlled camera:
The clean up process is a huge challenge to the world as a whole, but perhaps the following image places the initial effort made by the soviet government into perspective. Everything you see below can never be used again by human beings, owing to the radioactivity they came into contact with;
The above image represents only a fraction of the total machinery deployed in the aftermath of Chernobyl. The loss of machinery is, of course, nought when compared to the human suffering that this accident has caused. Chernobyl is simply too big an event to confine to a simple article, but I’ve done my best to attempt to do so, because in my personal view, humanity has discovered a power that it is, as yet, ill equipped to manage.
In terms of total human development and existence as we now understand it to be, Chernobyl happened a couple of minutes ago on the timeline.
There are some universal truths in engineering – if it can go wrong, it will, and, to expand on that, if there is any possibility – no matter how remote, that a mechanism or system can get into a pathological state, then that will eventually happen.
That isn’t to say that the engineers aren’t equipped with sufficient knowledge, quite the opposite. It speaks more to the utterly moribund state of the nuclear industry, political self interest, profit (never forget the profit…) and the status quo.
The regulatory side of the nuclear industry has seen many billions of dollars invested into itself. This means that no matter how inefficient a design may be, as long as it doesn’t have a propensity to go ‘pop’, it will probably be given a green light.
In terms of energy production, I personally, am a realist. I love renewable energy technologies, but, in my humble opinion, they simply aren’t currently capable of sustaining certain high load situations that our present rate of development and consumption demands. So that leaves fossil fuels… Or….
There are some really amazing research reactors in operation, most of which are generations ahead of the existing technology.
The LFTR reactor is a wonderful case in point – switch it off and go home. The cryogenically cooled plug at the base melts, and the Flouride/Thorium radioactive salt mix exits the base of the reactor, being dispersed into non-critical masses.
Then switch it on again when you go back to work… I had hoped to refrain from opinion in this article, but nuclear power is an extremely emotive topic, so I’ll end with something that I can’t find an answer to.
Only in the last 100 or so years have we been able to semi-reliably decipher Egyptian hieroglyphics.
Plutonium has a half life of 50,000 years – that basically means that after 50,000 years, half of it isn’t there any more, but the rest of it is just as radioactive. A simplistic interpretation, I know, but essentially valid.
So, 50,000 years from now, will our descendants take a look at a radiation symbol and think ‘What’s that’?, or will they think ‘Hang on, that’s not good…’
The assumption of continuity of knowledge through generations, and indeed civilisations, is probably the largest wholesale failing of mankind.
Text © K.I.S.S. 2017
If you have an interest in further material regarding Chernobyl and associated nuclear matters, may I draw your attention to the following links?
The day I blew up a nuclear reactor
A fascinating short video describing how an American physicist who was involved with experimental reactor safety, and pushed it to the limits. A mini Chernobyl.
Chernobyl – surviving disaster
A truly gripping drama describing the events following the accident. Stars Ade Edmonson, a U.K. comic, in a far from comedic role. Extremely emotive and with a high degree of factual content.
Zero hour – disaster at Chernobyl
A by the minute countdown of the sequence of events that let to the accident. Filmed in the control room of Chernobyl No.3 reactor, it lends itself to a verisimilitude of the actual event.
This is a 1969 safety film produced by Calder Hall, the then U.K. Plutonium processing plant.
A employee training film, it has laughable 1969 graphics and animations, but the science is bang on. The best description of criticality on the internet.