Suddenly a plane will fall from the sky: nuclear power plants and resistance to external threats

Table of contents:

Suddenly a plane will fall from the sky: nuclear power plants and resistance to external threats
Suddenly a plane will fall from the sky: nuclear power plants and resistance to external threats
Anonim

One of the most common questions about the safety of nuclear reactors is what happens if an earthquake, tsunami, or, for example, a plane crashes? Oddly enough, the designers of nuclear power plants prepared for almost all of these unlikely cases. And even in the case of such external influences, for which the designers did not prepare their reactors, they turned out to be quite safe for others. Let's try to understand in more detail how the nuclear power plant manages to achieve such results.

NPP

People's perceptions of a particular danger often do not correspond to reality. Nuclear power plants are one of the typical examples of this kind. We often hear: a plane may fall on the reactor (or terrorists may send it there). It is capable of failing due to an earthquake or tsunami. In an atomic war, they will become targets for enemy warheads - and thus seriously complicate the survival of any country that has them. Moreover, many people think that if the reactor is subjected to such a serious impact, it can itself explode like an atomic bomb.

The vitality and antiquity of these ideas is extraordinary: even in the first Bond film, released in 1962, a British government agent is engaged in sabotage at a nuclear power plant of a pool type (analogous to it actually existed in that era). He manages to overclock the reactor so that an explosion occurs on the island of the mysterious Doctor No from SPECTRA - and his entire criminal infrastructure comes to an end.

As funny as it may seem, this unreal story is based on the same ideas as the nightmares of our contemporaries described above: a lack of understanding of how reactors actually work.

Let's start with the simplest: no, a reactor cannot explode like an atomic bomb. This requires 47 kilograms of weapon-grade (practically pure) uranium-235, folded in a compact "slide" and then sharply compressed by the explosion. Modern reactors do not use fuel and with 50% enrichment, even 20% is a rarity. Most use fuel in which uranium-235 together with plutonium is no more than 5%. Whatever you do with such fuel, a nuclear explosion will not work out of it. Bond could not have set off a nuclear explosion on Dr. No's Island. Let's go back to more realistic scenarios.

Plane crash

This topic has received a lot of press attention since 2001. Typical judgments here are similar to these from bellona.ru: "Neither the operating, nor the nuclear power plants under construction have serious protection against this."

In fact, everything is not so: for example, for VVER-TOI reactors, protection is provided against a fall of a 20-ton fighter, and the fall of a 400-ton Boeing-747 aircraft is considered as a beyond design basis. But even before the appearance of such enhanced types of protection, there was no real danger from the fall of an airliner for a nuclear power plant.

Image

Ironically, a modern reactor simply doesn't need any special protection against an accidental plane crash - not even a deliberate attack by a passenger airliner like September 11, 2001. The reason is simple: the power unit protects the containment - an outer shell with reinforced concrete walls up to one and a half meters thick.

Let us remind you that airplanes are structures made of duralumin alloys with a typical outer shell thickness of 1.5 millimeters or a thousand times less. Inside, they are practically empty.The really dense parts of the plane are its motors, but in airliners they are spaced far to the side, which is why they cannot provide a blow with a "tightly clenched fist", only with spread fingers.

The chances of such a structure to break through a meter-long reinforced concrete are the same as for a chicken egg to break through a wall half a brick thick. Even if the egg hits the wall at a speed of 500 kilometers per hour - and the airliner can't get any more even in a dive - the brick wall will not fall apart from it.

However, not many people know how thick an airliner skin or reactor containment is. Many people start from the example of the Twin Towers - huge skyscrapers that were killed by attacks by planes under the control of terrorists. There, however, the collapse did not happen from the plane hitting the building, but from the fact that fuel was leaking from the destroyed airliners in the collision. It burned, the steel structures on which the skyscrapers are held warmed up to hundreds of degrees, lost strength and eventually collapsed. In nuclear power plants, this scenario is unrealistic: they are not skyscrapers, their shell is much thicker, so the containment strength cannot be disturbed by heating from the airliner fuel.

Image

But the public rarely thinks about it, so in 2002 in the United States, in connection with public fears, a study was conducted: what would happen if a Boeing 767 crashed into a building with a nuclear reactor inside. It turned out that the situation for the reactor is also facilitated by the fact that the airliner cannot hit it at full speed.

The fact is that when trying to dive at a large angle on such an aircraft, any pilot will either lose control of the aircraft (whose control system was not originally designed for such abrupt maneuvers), or even destroy the aircraft in the air. An attack is possible only with a gentle dive (that is, into the thickest, horizontal part of the containment) and at a moderate speed for an airliner. Otherwise (at high speed) it is difficult to realize precisely controlled flight in the surface layer, and without good controllability it will be difficult to "stick" the plane into a small object.

Fuel in this scenario, by the way, cannot drain from above onto the building: it will be located at the foot, where it will burn out, without seriously endangering either the containment, much less the reactor inside.

Unfortunately, no one has conducted a full-size test of this kind (only simulations). However, a fragment of a wall typical of containment was tested by an old Phantom fighter accelerated to 770 kilometers per hour: This fighter is smaller than airliners, but its motors (the densest part of the aircraft structure) are located very close to each other. Therefore, the effect of the impact of this fighter on reinforced concrete, oddly enough, is quite comparable to the impact on the same wall of a large liner.

After the test, the maximum track depth on reinforced concrete was 60 millimeters. Unsurprisingly, a 2012 French study also considered the destruction of containment from a plane crash dubious.

Well, we made sure that the aircraft itself will not be able to break through the containment. But pipes filled with water go through it - they can leak on impact, right? Purely theoretically, this is possible: if the liner accidentally hits just over the section where the pipes pass. But what will it do? Water from the second circuit is non-radioactive, and, to be honest, it is moderately dangerous from the first, because when it is bombarded with neutrons, a significant amount of long-lived radionuclides is simply not created (fortunately, only hydrogen and oxygen are made of atoms in water).

But what about the "radioactive water of Fukushima", the reader will ask? Alas, no way: the ever-renewing publications in the media about this water are solely the result of radiophobia. Yes, the core of the reactor at Fukushima has partially melted, and the seawater used to cool it will indeed sooner or later begin to be dumped into the ocean.But this will add to the local radiation background received by the inhabitants … 1, 2 microsieverts, that is, less than if they go to x-rays once a year. Moreover: even with this additive, the background in Fukushima will be much less than the natural and completely safe radiation background in a number of other regions of the planet.

The penultimate question: what if the plane falls on the containers where the spent nuclear fuel is stored (as we have already explained, it is incorrect to call it "nuclear waste")? Oddly enough, nothing again. These containers were tested for strength, running in them trains accelerated to high speeds, and could not inflict significant damage on them. The aircraft is made of a much thinner metal of noticeably lower density. In addition, it is lightweight (relative to rail facilities). Because of all this, the airliner will not be able to seriously damage the fuel in such a container.

And finally, the last question: what if the blow hits the control room and destroys it completely, with all the operators? In the case of current reactors, practically nothing. The fact is that now the rods above the core are holding electromagnets. Loss of power supply (likely with the destruction of the control room) or any dangerous unusual behavior of the reactor will lead to the fact that the power supplied to these electromagnets will be turned off, and the rods themselves, under the action of gravity alone, fall into the core, stopping the chain reaction there …

From all this, it becomes clear why terrorist attacks on nuclear power plants rarely get into the media today: there are not so many of them (too protected facility).

Earthquake: what will happen to the reactor after it

The resistance of an object to earthquakes directly depends on how prepared it is for various types of loads. Concrete does not bear the tensile load weakly, therefore it has been reinforced with steel reinforcement for a long time. In the case of a nuclear power plant, this reinforcement is pre-stressed - that is, concrete is poured onto pre-tensioned reinforcing cables. As a result, the building strength of even very old reactor facilities is enormous. In addition, special hydraulic shock absorbers connect the base plate and the station equipment into one whole, preventing it from moving even with very strong shocks.

Image

For the first time, such seismic resistance in the USSR was demonstrated by the Armenian NPP with two VVER-440 reactors built in the 1970s. On December 7, 1988, the Spitak earthquake happened near it. At the epicenter, it gave seven points on the Richter scale, and at the NPP itself - 5.5 points. A total of 25 thousand people died in Armenia then, and not a single one on the territory of the nuclear power plant.

But if the reactors turned out to be durable, then this is already more difficult to say about the Soviet educational foundation. The fact is that at that time in the USSR, anti-nuclear sentiments were at their peak and the press regularly and successfully intimidated the society, talking about the dangers of nuclear energy - it is true, which is typical, more and more without numbers, but with high quality pressure on emotions. From this, a significant part of the unskilled personnel of the Armenian NPP simply fled from their jobs, which required the transfer of personnel from the Kola Peninsula.

Image

The politicians of the late USSR, as you might guess, were the same prey of the media as everyone else. Therefore, without hesitation, they made a decision to stop the station, which was operating at that time absolutely normally, which in fact “did not notice” the earthquake itself. Justification? "Taking into account the general seismic situation in connection with the earthquake in the territory of the Armenian SSR … stop the first unit of the ANPP."

Think about it: the station has survived the event that killed 25 thousand people in its vicinity - not a single crack anywhere, no damage. How can you “given the seismic situation” close what has brilliantly shown the ability to pass through the complexities of such an environment? By the way, the station was designed for a 9-point earthquake - that is, much more powerful than what happened on the territory of Armenia in its history.

Of course, an unreasonable decision was quite expensive. After stopping, it was decided to conduct a "research" - to cut out pieces from the steam generators to see if there were any imperceptible cracks in them. Strictly speaking, such things can be investigated without destruction, but in the era of anti-nuclear sentiments, it seemed obvious that nuclear power plants would never be launched, so the "research" was carried out, which caused the first unit to become unworkable. They began to cut off part of the equipment from it and sell it cheaply - fortunately, the legal and commercial culture of that time did not see anything special in such actions.

However, in the 1990s, economic difficulties began in Armenia, plus some of the traditional routes for the supply of fuel were lost due to the blockade. Therefore, by 1995, the nuclear power plant was restarted - albeit at half capacity, because the first power unit, as we noted above, was successfully destroyed. Today, only the second is working, providing 40% of the republic's electricity.

Yet nuclear power plants had to show their ability to survive a 9-point earthquake. It happened in the Fukushima area. Usually, the events there are assessed as the worst catastrophe in the history of nuclear energy in the 21st century. The nuclear power plant turned out to be close to the epicenter of the strongest earthquake in the history of Japan, but from the earthquake itself literally nothing, not a single object, was out of order. Meanwhile, the range of seismic activity was enormous: from the earthquake itself and the subsequent tsunami, 18, 5 thousand Japanese died or went missing.

And what about the tsunami?

Indeed, one cannot but admit that a tsunami, if it is not provided for by the project, is very dangerous - however, not only for reactors, but for anyone. But the whole question is how exactly it is dangerous.

The well-known events at the Fukushima Daichi nuclear power plant are usually perceived as some kind of disaster. Recall: although the station calmly endured a nine-point earthquake without any problems - and the first tsunami wave four meters high (extremely strong by ordinary standards) - the second wave of 15 meters exceeded the height of the protective dam of 5.7 meters. Therefore, she flooded a large number of auxiliary buildings of the station. Including its diesel generators, which were supposed to provide cooling of the reactors in the event of a complete loss of power supply. The loss, of course, happened: the tsunami partially cut power lines.

Image

In general, there could have been no further serious problems - if the American designers of this rather old station had made its design more thoughtful. For some reason, the standby diesel generators in it, feeding the cooling pumps in the reactors, were located in the basement, and not above ground level, like the rest of the station. Naturally, the basements were flooded with water. Strictly speaking, in areas where flooding is possible, standby generators are located just so that they are not flooded with water. But Fukushima designed the way it was designed, which led to the accident.

Immediately after the start of the tremors, the local reactors were protected in case of severe earthquakes. The rods with the neutron absorbing substance were introduced into the core, that is, the reactors were drowned out.

However, after shutdown, the fuel still gives off some heat, so the reactors need to be cooled down for some time. Big problems have arisen with discouragement. The sealed containment buildings of the Fukushima reactors were designed for a low pressure of five to six atmospheres, and everything that is more, the emergency valves had to be vented into the atmosphere so that the containment would not "burst" by this off-design pressure. This would not be a problem if, after the loss of power, the Japanese reactors could remove the residual heat from the TVEL (fuel element with nuclear fuel inside) themselves, without external water replenishment from pumps outside the containment.

Image

But they could not: Japanese reactors (in fact, American design half a century ago) had only one cooling circuit.The Russian VVER-type reactors under construction today have two-circuit schemes, so there is much more water in the cooling system, and heat can be removed without the participation of any external sources of water supply for 72 hours. There are three cooling circuits at the Beloyarsk NPP.

Another important point: the Fukushima reactor is boiling, that is, the water in it boils, and if it overheats, the heat removal from the fuel rod can sharply decrease. After all, when all the water boils off into steam, the thermal conductivity of which is much lower, the heat removal from the vigorous fuel will fall.

In such a situation, the zirconium shells of the fuel elements react with water vapor and form oxygen and hydrogen - an extremely explosive mixture. At Fukushima, it accumulated inside the reactors, and when sparks were supplied to the objects, it also exploded. At the same time, the destruction of the containments did not happen, but in the very fact of the explosion, of course, there is nothing good, even if no one died from it.

Image

However, on modern VVER-type reactors, such a scenario is fundamentally impossible - and here's why. The VVER container has a volume of 75 thousand cubic meters and can withstand an internal pressure of 50 tons per square meter. Consequently, even if a VVER were to suddenly find themselves where tsunamis are possible and were built without a protective dam, then the complete deprivation of its power supply would only lead to boiling water from the primary circuit - and not immediately, but strongly after 72 hours. But even after complete boiling off, the water vapor could not break the containment from the inside - unlike its Japanese counterpart, its size and strength allow it to keep everything inside.

In other words: yes, if the external coolant for cooling the reactor is not supplied for three days - only after that the water will boil - then the fuel elements may overheat with their damage. Zirconium from fuel element cladding is able to react with water and give hydrogen - but in the upper part of the VVER there are hydrogen absorbing reagents, so hydrogen cannot accumulate here in large quantities. This is the end of the list of realistic consequences of any tsunami for modern reactors: in the extreme case, the reactor will "ruin" its core, but will not release anything noticeably radioactive outward.

Invaluated safety of old reactors

Finally, it is worth paying attention to the following. Although the Fukushima reactors were of an extremely outdated design and therefore much less safe than modern ones (the same VVER-1200), oddly enough, they turned out to be very safe for the population during the tsunami.

It sounds strange: after all, the media constantly trumpets us that Fukushima was a terrible nuclear disaster that made vast territories uninhabited and still continues to pollute the ocean with radioactive water. How can you call its reactors "safe for the population"? The answer to this question is simple: numbers.

When the media talk about the Fukushima horrors, they carefully avoid giving specific numbers - the level of radioactive contamination from the accident. Let's make up for their flaw: people in Fukushima Prefecture received and will receive 10 millisieverts in their entire lives as a result of this accident.

Is it a lot or a little? The natural background radiation in Japan is 3.83 millisieverts per year. That is, in the most seemingly affected part of the country, the radiation contamination turned out to be equal to 2.5 years of local background radiation. If we take the United States, where, due to the way of life, the radiation background is 6, 24 millisieverts per year, then we are talking about 1, 5 years of the normal background.

Perhaps the normal background is so much, and it is even slightly dangerous to exceed it? It is known for certain that this is not the case. For example, in 30 years of operation, commercial airline pilots receive 50 millisieverts - five times more than the "victims" from Fukushima Prefecture (we apologize for the quotation marks, but at such a dose it would be dishonest to write this word without them). Maybe the pilots are madly risking their lives and everyone dies as one early? Alas, in practice, their average life expectancy is four to five years higher than that of the general population.

What are the pilots.One computed tomography gives from 10 to 30 millisieverts - that is, in a matter of minutes it delivers more radiation to the body than Fukushima's "victims" receive in a lifetime. People who fled the prefecture in 2011, many of whom never returned to their homes, are afraid of radiation from the station, but no one has ever heard of them being afraid of CT scans. Why is that?

The thing is that modern society is chronically poorly informed: it draws information from the press, and that … Well, to be honest, it lives on clicks. It is clear that writing about Fukushima means getting more clicks, and the journalist himself is not always hardworking enough to find the numbers of doses to the population from the accident and understand that they are lower in their entire life than from one (!) Computed tomography (quite harmless to health).

Of course, the NPP personnel received somewhat large doses - six people received from 309 to 678 millisieverts, which is already quite significant. For comparison, it can be indicated that a NASA astronaut during his career should not receive more than 500 millisieverts in any year of service - that is, a couple of workers at the local nuclear power plant still went beyond the limits of completely safe exposure. But none of these workers have yet died from cancer or other consequences of the radiation they received. They also have no chronic health problems that could be associated with radiation.

Why? The fact is that even 500 millisieverts and more do not always lead to cancer or premature death. In the 1940s in the United States, during an experiment on what was believed to be a terminally ill person, he was injected intravenously with plutonium-238, which caused him to receive 3,000 millisieverts annually, and 64 thousand millisieverts in his life as a whole. Nevertheless, he died at 79 years old - without cancer and other noticeable traces of radiation exposure.

And this is not the only example. Let's say a person who smokes a pack a day receives 53 millisieverts a year from cigarette smoke into the lungs (cigarettes contain a number of fissile isotopes, in particular polonium). That is, in 19 years of smoking, he will receive a dose higher than any Fukushima employee or NASA astronaut.

The radiation received by a smoker from cigarettes is an order of magnitude higher than what he receives from the natural background radiation, and many times higher than the radiation received by residents of Fukushima Prefecture. But has anyone seen at least one smoker who is worried about this? First, they don't know about it, and what we don't know doesn't bother us. Secondly, even if they suddenly found out about it, they would also know that almost all the risk from smoking is not given by this dose of radiation, but much more dangerous microparticles that cause cardiovascular diseases.

The statements in the press that one of the Fukushima workers allegedly died of lung cancer a few years after the events, alas, do not stand up to scrutiny. First, more than 3,500 people were eliminated from the accident, and the risk of dying from cancer for a Japanese is about 20%. Over the nine years that have passed since then, one of the staff must have died from him. Secondly, the deceased received much less than the peak values ​​mentioned above, that is, his specific risks were minimal. Third, he died from lung cancer, not from leukemia: in other words, from a type of cancer that is not a consequence of radiation accidents.

But what about the periodic publications about the threat of radioactive water, which is about to be dumped from the territory of this nuclear power plant into the Pacific Ocean? Everything is quite simple: the water that was used to cool the molten cores of local reactors is indeed slightly radioactive, but just slightly. Its complete discharge into the ocean will increase the dose to residents of Fukushima Prefecture by 2.01 microsievert. Micro is not milli. That is, it will entail an increase in the annual background dose of radiation to the Japanese living there by less than one thousandth of the usual radiation background. Such an excess is quite safe for health and is much inferior to the loads from air travel. It will not be able to noticeably harm marine life.

In general, it is difficult to wonder that the World Health Organization report on the accident honestly wrote: the doses received from it are so small that the consequences will be below the levels that can be detected by observation or statistically.

Image

Of course, this does not mean that the events in Fukushima did not kill many Japanese: undoubtedly, yes. That's just not radiation, but a "mental epidemic". The fact is that politicians do not fall on our planet from outer space, but are obtained from ordinary people. Therefore, just like ordinary people, they have no idea how many millisieverts threaten a person in the Fukushima area and how much he can get from a harmless trip to computed tomography.

Therefore, it seemed to them that the people in the prefecture were in dire danger. And 164 thousand locals were evacuated. Evacuation-related stress and trauma, as well as poor care for the elderly and sick, resulted in 2,259 excess deaths (Japanese government official estimates).

The problem is that these people cannot be written down as victims of radiation: they are victims of poor education. And not even their own, but Japanese journalists and authorities - it was their gaps in knowledge about the world that led to the decision to evacuate.

As a 2016 scientific paper published in the peer-reviewed journal Process Safety and Environmental Protection concludes, the evacuation ultimately caused many deaths and a marked reduction in the life expectancy of those evacuated. And this, the authors emphasize, despite the fact that in fact there was no need for it. In an amicable way, those who made such a decision should be judged, but, alas, there is no one to do it: judges do not read scientific journals.

From safety for others to safety for yourself

Analysis of the possibilities of terrorist attacks on nuclear power plants, the impact on them of falling aircraft and earthquakes shows that even the oldest nuclear power plants, built in the 60s and 70s, do not pose any threat to others in the event of all these events.

The only case when an external threat managed to bring a nuclear power plant out of service is a unique tsunami that happens in Japan less than once every thousand years. The fifteen-meter wave from it is really dangerous, but even it could only disable the reactors: they “died” at the combat post, but not a single person died. Against the background of 18, 5 thousand deaths from those events at non-nuclear Japanese facilities, Fukushima looks good. It shows that the degree of stability of the nuclear power industry in the event of external threats is indeed seriously underestimated.

This does not mean that nuclear power plants have nowhere to grow. In the Fukushima situation, new designs of the VVER-1200 type would not only not cause harm to anyone, but they would not fail themselves with a high probability: for three days they would be discouraged due to the “built-in” passive safety. And even if the working generators had not been brought up during these days, the reactor itself would have been able to keep the situation from an explosion of hydrogen (due to the built-in absorbers of this gas). Finally, after Fukushima, nuclear power plants in the tsunami zone will be built only if there is a dam that protects even from such a wave, which happens once in a thousand years.

Popular by topic