Fast neutron reactors are a unique development of Russian scientists and the future of the entire nuclear power industry

The peaceful atom is one of the pillars of world energy, without which modern society is simply impossible. Despite all the advantages of existing nuclear power plants, the main flaw has been and remains the disposal of spent nuclear fuel.

It seems that this problem will also be solved - thanks to the unique Russian development of a closed nuclear fuel cycle, the implementation of which is possible in nuclear reactors using fast neutrons.

What is the problem of modern nuclear power

So, the peaceful atom has been serving mankind for generating electricity throughout the world for more than a dozen years. But there is one very serious problem. Not all natural uranium is suitable as fuel for nuclear reactors.

Uranium-238 is widespread in nature (92 protons, 146 neutrons), and its share in the world's reserves is 99.3% of the total uranium on Earth. But it is just not suitable for nuclear reactors as fuel.

Only the remaining 0.7% of the world supply in the form of uranium-235 (92 protons, 143 neutrons) can serve as fuel. But even this remaining part of the uranium cannot be simply taken and loaded into the reactor. It must be pre-enriched and the share of uranium-235 in the total mass of uranium-238 increased by about 700 times.

It turns out that, despite the huge world reserves, uranium that is really suitable for fuel will be enough, according to average calculations, for only 50 years.

Everything is not as gloomy as it seems at first glance. Uranium-238 can still be adapted for nuclear reactors. True, for this it is necessary to convert uranium-238 into plutonium-239, and this process is possible only when exposed to fast neutrons.

As it turns out, this transformation is not easy. After all, most modern reactors operate on "slow" neutrons, which are deliberately slowed down, since uranium-235 "does not want to communicate" with fast neutrons. But uranium-238, on the contrary, is not involved in the transformation process on slow neutrons.

It is not economically feasible to carry out the transformation of uranium-238 into plutonium-239 separately. It is much more efficient to use for this the so-called extra neutrons, which are formed during the decay reaction. Therefore, in modern reactors, they are specially removed using absorbers.

So we need to combine "junk" uranium-238 and "correct" uranium-235 in one place - an atomic reactor. And then it will be possible to both generate electricity and specifically transform "unnecessary" uranium-238 into new nuclear fuel for reactors. But a prerequisite for this is the fact that it (the reactor) must operate on fast neutrons.

But creating such a really working fast neutron reactor turned out to be a big problem for many engineers. And only Russian engineers-scientists coped with the task.

Fast neutron reactors, what is their feature

So, we need a reactor that runs on uranium-235 and at the same time, we need to make it work on fast neutrons. In order for this to be possible, it is necessary to significantly increase the density of the neutron flux (so that uranium-235 becomes more willing to interact with fast neutrons).

This means that it will be necessary to use a more enriched fuel, while the temperature regime and neutron fluxes will be significantly tougher - more stable materials will be needed.

In addition, materials that will slow down neutrons should be avoided. That is, the classic version - water - is not suitable in this case, since it perfectly slows down neutrons.

That is why mercury was used as a coolant in the early stages of developing fast reactors, but this option was quickly abandoned due to the high toxicity of the metal.

At the next stages of the experiments, they tried such metals as lead, bismuth and sodium.

The most promising materials were found to be sodium and lead. And at the first stage, Soviet engineers managed to "tame" sodium.

The first commercial, fully operational fast neutron reactor was the Soviet BN-600 reactor. And already in 2015, Rosatom launched the BN-800 (sodium) reactor. This is a unique reactor of its kind, which is already adapted to operate on plutonium fuel with a full closed breeding cycle.

What is the advantage of fast reactors

Preliminary calculations show that thanks to this technology, the percentage of nuclear fuel suitable for reactors rises sharply from a modest 0.7% to 30%.

Consequently, the effective fuel reserves will increase by about 43 times, which means that they should be sufficient not for some 50 years, but for more than two millennia. I think there is a difference even with a very rough calculation.

In addition, such reactors are capable of fully functioning on spent nuclear fuel from "slow" reactors, which promises a solution to the biggest headache of environmentalists - how to dispose of spent nuclear fuel.

Also, such reactors are much safer. After all, they use sodium instead of heated water under high pressure. Sodium becomes liquid at 100 degrees Celsius, and goes to the boiling stage only at 900 degrees.

Let's remember how the cooling system works on "conventional" nuclear reactors. There, water under enormous pressure acts as a coolant. Obviously, high pressure is a high risk of depressurization and accident.

There are no such problems with sodium. Since the boiling point is high, it can be kept at normal pressure, which means there is no chance of a breakout and accident.

Even in the event of an abnormal situation, the reactivity of sodium will also play in favor of safety. When interacting with oxygen and moisture vapor in the atmosphere, sodium will be bound into persistent chemical compounds that will remain on the territory of the station, and will not scatter around the district, spreading radioactive pollution.

Russia is ahead of the rest

Despite numerous attempts by various countries, only Russia, and in particular Rosatom, has a full-fledged commercial version of a fast neutron reactor.

Indeed, even the French (with their promising development of the "Phoenix reactor") did not manage to deal with the problem of periodic operation of protection systems, and they stopped the project in 2010.

The Japanese also tested their own version - the Monju reactor, but after a series of accidents they decided to disassemble it.

The Indians also wanted to create their own fast neutron reactor, but nothing happened.

In Russia, the technology is developing smoothly, and work is already underway on the BN-1200 fast reactor project, in which molten lead is used as a coolant. According to the plan, it will be fully operational by 2030.

It turns out that Russia is the only country that can really make nuclear energy efficient and truly safe due to a unique design - a fast neutron reactor.