Nuclear “Perpetual Motion machine” in my small town
…how do I feel about an experimental nuclear reactor 10 kilometers from my home?
Of course, this has been discussed for a long time. And the construction site for the new nuclear facility was laid several years ago. With the latest news, it becomes obvious that the closed nuclear town in the center of Siberia, where I live, will not open its borders.
I recommend you to see my article with a short story about Seversk, a closed city that a few years ago was not even on the maps:
The first concrete pouring at the construction site of the BREST-300-OD pilot power unit is scheduled for June 8 in the city of Seversk, Tomsk region. A new fast-neutron nuclear reactor with a lead coolant should become a demonstrator of a completely unique technology on a global scale. This is a completely closed nuclear fuel cycle.
On the common site, in addition to the power reactor itself, a nuclear fuel plant and a spent fuel cell recycling facility will be built, closed in a single cycle. This will not only give the BREST reactor full fuel independence, but also allow it to develop new nuclear fuel for other reactors
To date, only Russia has operating fast neutron reactors. BREST is the second generation of such reactors, which surpasses the first in all standards — efficiency, safety and reduction of environmental impact.
Let’s see what they tell us about this new experimental type of reactor:
Lead instead of water
The basis of any nuclear chain reaction is neutral particles from the nucleus of an atom-neutrons. The hit of a neutron in the nucleus of the isotope of uranium-235 causes its spontaneous fission, in which it throws out along with the fragments of fission and 2–3 new neutrons.
It is not difficult to understand that if all the neutrons were disposed of in new fissions, the number of fissionable uranium atoms in such a reaction would grow exponentially. This is exactly what happens in a nuclear bomb, where a chain reaction very quickly turns into an explosion of enormous power. But in an energy reactor, the “extra” neutrons are usually somehow removed, so that the chain reaction goes on, but does not gain excessive power.
A free neutron, although it has no electric charge and can move in any direction from the decay point, does not live long. Usually it is absorbed by neighboring atoms — fuel, reactor structures, its coolant. If the neutron is absorbed by the reactor structure or the coolant, this leads to “induced” radioactivity, when neutrons turn stable nuclei into unstable ones, prone to subsequent decay. This effect is extremely unpleasant, because these nuclei are radioactive, so it is always sought to minimize.
In BREST, lead coolant is used for this purpose. Lead is one of the most suitable elements of the Periodic Table for this purpose: it is radiation-resistant and weakly activated. This means that it is extremely reluctant to absorb neutrons and practically does not accumulate induced radioactivity. Therefore, the coolant of the new reactor can be easily disposed of after the end of its service life.
In addition, lead is chemically passive in contact with water and air — unlike sodium, which was used in first-generation fast reactors, such as the BN-800 operating in Russia. In the event of a violation of the tightness of the circuit in BREST, the coolant will simply flow out, cool down and go into a solid state, and also close the leak site with a lead “plug”.
Another feature of lead is its high boiling point. It is much higher than that of plain water, which is common for reactor cooling systems today. Lead in BREST circulates at a temperature of 1751 °C, being in a liquid state near the boiling point. Recall that the temperature difference is the basis of any thermodynamic cycle: the higher it is, the higher the efficiency of the installation.
For comparison, existing nuclear power plants never heat the primary water above 374 °C, or the so-called “critical point”, after which the water passes into a very unstable state, midway between liquid and steam. This is due, again, to safety: the water vapor in the reactor sharply unbalances the chain reaction.
The molten lead used in BREST is not particularly convenient for the operation of turbines, so they will heat the water of the second circuit. Due to the high temperature of the lead, the resulting water vapor will have supercritical parameters-up to 600 °C. This will allow the power unit with the BREST reactor to have an electrical efficiency limited only by the design of the steam turbine, which is 40–45% — one and a half times higher than the parameters of modern nuclear power plants.
In the future, the use of lead energy will completely eliminate water vapor in the second circuit. For example, molten lead can be used to power a closed-cycle gas turbine, whose efficiency is even higher than that of a supercritical steam steam turbine.
Don’t lose the neutrons!
The use of lead makes it possible to direct almost all neutrons released during nuclear fission back to the fuel assemblies. This is due to another pleasant property of lead — it quickly slows down neutrons, being a good moderator, unlike the usual water of modern nuclear power plants.
Next, we need to go to strict physics, describing the entire chain reaction of uranium.
So, the fission of each uranium-235 nucleus produces sometimes 2, and sometimes 3 neutrons, on average — 2.45. One neutron to maintain a stable chain reaction always needs to be spent on fission of the next nucleus. But here there is a special feature: in 18% of cases, uranium-235, capturing a neutron, does not divide, but turns into a parasitic isotope — uranium-236. With the latter, there is almost nothing to do: it, like lead, does not like new neutrons and reluctantly captures them, and decays for a very long time — more than 23 million years.
Therefore, from the initial 2.45 neutrons, we subtract 1.2 — that is how many neutrons should be spent on new fission of uranium nuclei. The remaining 1.25 neutrons can be used. As already mentioned, in conventional nuclear power plants, these neutrons are simply absorbed somewhere or even fly out of the reactor, into its biological defense.
Immediately after fission, it is quite easy for neutrons to do this: uranium-235 is divided with the radiation of high-energy,” fast “neutrons, which is why BREST got its name — “Fast reactor with Lead Coolant”. Directly with such fast neutrons, uranium-235 does not divide, for its fission requires low-energy, thermal neutrons. And lead, as already mentioned, is good at slowing down fast neutrons to thermal ones, allowing uranium-235 to divide in a controlled chain reaction.
But the remaining fast 1.25 neutrons in BREST are “disposed” into the nuclei of another isotope of uranium-uranium-238. This isotope, like uranium-236, acts as a pure neutron absorber, but the effect of such absorption is much more interesting. The absorption of fast neutrons by uranium-238 is very easy: it is very “greedy” for high-energy particles flying through it.
By capturing a neutron, uranium-238 turns into an isotope of another chemical element — plutonium-239. This is the basis of all nuclear weapons in the modern world, but in Russia it began to be used as fuel for nuclear reactors: in them plutonium burns no worse than uranium. So it turns out that, ideally, for every separated nucleus of uranium-235, we can get 1.25 nuclei of new plutonium-239, which miraculously appeared right in the reactor from “waste” uranium-238, unsuitable for conventional fission.
Of course, the theoretical limit is unattainable in practice. Even in Brest, neutrons are actively absorbed by the reactor structures, fly out of the core, and react with fission fragments. However, the BREST power unit, due to its well-thought — out design, the special arrangement of fuel cells and the use of a weakly activated lead coolant, allows you to get a fuel reproduction coefficient much higher than one-according to calculations, up to 1.2, which is already very close to the theoretical limit.
Once we load nuclear fuel at the BREST site, we can almost forget about the needs of such a reactor for fresh fuel for centuries to come, and even get about 20% of the new fissile material from each cycle inside the reactor. A kind of “perpetual motion machine”, created in strict accordance with the peculiarities of nuclear physics.
Why are fast neutron reactors so far behind?
The main difficulty in mastering such an attractive (on paper) closed nuclear cycle has always been the design and engineering complexity of fast neutron reactors. If we simplify it, we can say that a fast neutron reactor is much more “hot stuff” than a standard nuclear power unit that uses slow, thermal neutrons and simple water as a coolant.
In fast-neutron reactors, everything is much more intense: it is permeated by destructive neutron fluxes, a coolant with exorbitant temperatures circulates inside, and nuclear reactions in its core are very fast and unpredictable.
(It’s at this point that I literally begin to be tormented by all sorts of doubts… Still, it’s only 10 kilometers to the door of my house. )
Because of this, the technical difficulties and economic costs of creating a full-scale fast-neutron power plant were an order of magnitude higher than for conventional thermal-neutron reactors, which are now the vast majority in the world. Whereas fast neutron reactors are still isolated experimental installations.
The developers encountered problems even on the first generation of fast neutron reactors, which used liquid sodium as a coolant. Of the four countries that started the construction of such reactors in the world, the existing power units, namely BN-350, BN-600 and BN-800, were built only in the USSR/Of Russia. But in the United States, France and Japan, all experimental fast-neutron reactors either did not enter service at all, or were stopped shortly after launch due to a bunch of identified engineering and technological problems.
Having started the BREST project and successfully mastered the technology of liquid sodium in fast neutron reactors, Russia is moving to the next, second generation of power units using a much safer and more promising lead coolant. This is indeed the energy of the future: so far, the availability of uranium-235 has not yet reached the critical values for the industry, but its reserves are not infinite. Sooner or later, the nuclear power industry will face a shortage of cheap natural uranium-235, and then the BREST-type reactors will be the only way out of a difficult situation. After all, they produce nuclear fuel themselves and do not need a uranium mine to replenish its reserves.
…such science-fiction miracles are promised to us by the designers of a new type of reactor. Of course, I am an absolute simpleton in serious science, for me it all sounds like the promise of some”perpetual motion machine”. And in physics classes at school, I was taught that the laws of thermodynamics are unchangeable and “perpetual motion” can not be.
However, in fact, I, as a resident of the city, first of all, of course, do not care about this at all. I live on the extreme street of the city on the side of the industrial zone. From the construction site of the new reactor, near which I have repeatedly visited, to the entrance door of my house in a straight line is only 10 kilometers.
And I have questions, for example, why in other countries work on fast neutron reactors was closed?
There are arguments-doubts about the sad experience of the past, the Chernobyl disaster is now heard, but one of the bricks in the series of initial causes that contributed to that tragedy was the very design of the station with technical solutions that significantly reduced the cost of production and operation of the reactor, but at the same time significantly increased the requirements for compliance with safety measures and maintaining the reactor in a narrower specified regulatory state, violation of which in the first place led to the Chernobyl nuclear power plant with a terrible disaster. And will they now want to save money again and get a cheap but unsafe atom?
Here I look at the regulatory documents and do not understand, does the planned reactor correspond to them?
According to the NP-032–01 — “Placement of nuclear power plants. The main criteria and requirements for the placement of nuclear power plants” and SPAS-99 the following basic requirements are imposed on the placement of nuclear power plants (among other things, I highlighted what is striking even to such a simple layman as me):
within a radius of 25 km from the planned site (the zone of planning of mandatory evacuation measures), the average population density calculated for the entire period of operation of the NPP should not exceed 100 people/km2
and Table 2:
Minimum distances from nuclear power plants to settlements, depending on the number of people:
Number of population Nuclear power plant capacity
up to 4 GW
100 to 500,000 people — 25 km
Seversk is a fairly compact city with a high population density for its size. There are more than 120 thousand inhabitants in Seversk. 10 kilometers from the reactor to my house…
And, again, from school physics and chemistry courses, everyone knows about the toxicity of lead vapors.
On the Internet, you can easily find articles by well-known critics of fast neutron reactors, and the questions they raise, so far, as I understand, do not have an answer.
General Designer of” Afrikantov OKBM “ V. I. Kostin designates the following unsolved technical problems:
maintaining the oxygen concentration necessary to limit the corrosive effect of the coolant on structural materials (~ 10 6 wt. %) with the provision of appropriate control in the coolant, evenly in all places of its location (this is especially important for an integrated single-hull layout containing stagnant zones);
the radiological danger of RU with a “heavy” heat carrier, since these heat carriers do not retain the fission products-caesium and iodine, which pass into the gas circuit, from where they can go beyond the first circuit. In addition, when the lead-bismuth coolant is irradiated, a large amount of radioactive polonium is additionally formed (this process is also characteristic of the lead coolant). To this should be added the problem of tritium accumulation in the second (steam-water) circuit of these reactor plants;
large energy and time costs for melting and maintaining the coolant in the liquid state (it will take 7 months to warm up the reactor at the BREST-OD-300 reactor plant according to the project);
the toxicity of “heavy” heat carriers and the formation of long-lived isotopes of alpha-active lead, alpha — and beta-active bismuth with a half-life of more than 106 years, which exacerbates the problem of their disposal after the termination of operation of the reactor.
Responding to the criticism of V. I. Kostin, the creators of BREST-300 note that Kostin is an interested person who develops and promotes competitive development, but still questions remain.
And there is also a published opinion of a specialist in the field of nuclear physics, academician of the Russian Academy of Sciences, vice-president of the Kurchatov Institute Nikolai Ponomarev-Stepny, who notes the lack of development of the new technology and points out the following questions:
in a large volume of the integrated circuit “BREST”, the uniformity of maintaining the oxygen potential in a narrow allowed range is not ensured (if it is confirmed). To ensure the efficiency of the fuel elements, it is necessary to find the optimal oxygen content in the coolant for a given level and temperature range and to maintain it stably at this level throughout the entire life of the reactor plant;
the operability of structural materials in lead at the accepted temperature and under high neutron irradiation is not justified (molten lead causes severe corrosion of structural materials);
the effect of irradiation in real reactor conditions on the behavior of fuel elements and fuel composition in lead has not been studied;
the problem of mixed nitride fuel itself requires considerable effort and time to solve it;
technical solutions for fuel processing are at the initial stage of development.
I understand that innovation, especially in such a dangerous environment as nuclear power, always looks scary and someone has to try and test new things for global progress. But the guinea pig, especially without any reward other than the hope for the development of the region’s economy, is somehow quite uncomfortable…
Dear reader, what do you think? Next to me, history is being created and a new revolutionary type of nuclear power plant will be launched for the benefit of human civilization, or in a few years you will see a report of a nuclear disaster on the pages of my blog? If I have time to write something, of course, it’s only ten kilometers from the reactor to the door of my house…
