Could fast neutron reactors take the place of EPRs?

Could fast neutron reactors take the place of EPRs?

Could fast neutron reactors take the place of EPRs?

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[EN VIDÉO] The difference between nuclear fusion and nuclear fission
What is the difference between fission and nuclear fusion? Both involve reactions to the atomic nucleus, but fusion involves joining two light nuclei, where fission breaks a heavy nucleus into two lighter nuclei.

They were announced by President Emmanuel Macron in February 2022: between 6 and 14 EPR (European pressurized reactor Where is it Evolutionary power reactor) will be built by 2040 in order to maintain the nuclear as the main source of electricity in France. These reactors are based on the same principle as those currently used: da heat is created in the tank by nuclear reactionsthen extracted from kept water liquid below high pressure. This water circulates in a closed circuit in the primary circuit, itself in indirect contact with a secondary circuit. It cools in contact with it, transmitting its heat to the water that circulates there. The latter then vaporizes and spins a turbine which drives a alternator : Electricity is generated!

Uranium resources for less than 100 years

This reactor technology has been favored by France for decades. Since then, a lot of feedback has been available which in particular has made it possible to improve the plant safety. So why change technology when you know how to use the existing one perfectly?

Many reasons. The wastefirst of all: like any industrial exploitation, the nuclear center generate waste. Except most of them are radioactive, some of which have a duration of radiotoxicity for hundreds or even thousands of years. But also the relative cost to the price of materials first, because the resources in uranium they are limited. This element, the heaviest in its natural state on Earth, is 10,000 times rarer than iron. According to the International Atomic Energy Agency (IAEA), uranium resources allow it at least meet demand by 2040. But what about the distant future? Futura questioned a CEA expert about another reactor technology: fast neutron reactors.

This concept is as old as pressurized water reactors (REPRESENTATIVE). Called RNR for fast neutron reactors, these reactors use a different cooling and fuel technique than PWRs, in particular, ” make better use of it atoms fissile and fertile fuel compared to pressurized water reactors, because fast neutrons cause the fission of more nuclei “, explains Eric Abonneau, program assistant 4And generation of the CEA. In fact, in a pressurized water reactor, the neutrons are slowed down by the liquid water that circulates in the tank. This allows them a higher probability (also called cross section) of fission than with a fast neutron, when they encounter an atom of uranium 235 o plutonium 239, fissile isotopes of uranium and plutonium.

But, contrary to the slowed down neutrons, called “thermal”, the fast neutrons they have the ability to fission many more isotopes in addition to those called fissile, because they have a greater power. So, in a fast neutron reactor, on the contrary, “ fast neutron reactors do not require a moderator because neutrons do not have to be slowed down “, E.Abonneau continues. They therefore only require a cooling liquid to carry heat.

The internal inlet temperature is about 390 ° C and the outlet temperature is 550 ° C. The heat is transmitted to a secondary circuit, also in sodium. Subsequently, the secondary circuit exchanges its heat with a tertiary circuit, or through a sodium / water exchanger, or through a sodium / gas exchanger. ” Furthermore, this possibility of fissioning many more nuclei would alleviate the problem of uranium resources: “We could reuse the plutonium that comes from PWRs, as well as use the depleted uranium that is currently stored in France: we would get a much better lifespan”, explains E.Abonneau.

Undeniable advantages for fast but not sufficiently competitive neutron reactors

This technology aroused great interest in the early days of civilian nuclear power.Very soon, scientists realized the interest of spectrum fast for neutrons. From the 1960s we started using fast neutron reactors: first with Rhapsodie, then Phénix and Superphénix ”. explains E.Abonneau. The reactors have been running for a few decades in total, but today all have stopped. ” For SuperPhénix, in the 1990s we had initiated an instruction for its restart, but a political decision led to the closure of the reactor. “

However, while feedback on the experience is minimal compared to that of PWRs, the RNR have undeniable advantages, both in terms of operation and design: “The RNRs operate at atmospheric pressureunlike PWRs where the pressure imposes thick hulls ”. Advantages that, for the moment, do not weigh on PWRs, but could in the near future, in particular for the issue of raw material resources: “With uranium shortages, PWRs will face shortages of supply. It can remain between 50 and 100 years, but no longer. The FNRs could last several thousand years, because they can be isogenerators: they produce as much fissile material as they consume ”.

Despite everything, the question of the coolant remains: sodium in most technologies, a lot reagent with water eair. In other RNRs, leadlead-bismuth or even molten salts, as E. Abonneau explains: “Recently we have also focused on another technology: molten salt reactors. The fuel is there in liquid form, which has purported safety benefits but also brings a number of locks technologies to be removed (corrosion, materials, etc.).

Finally, the question may arise once PWRs lose their competitiveness. Right now, “even if the construction of an RNR costs more than that of a PWR, it will be much more advantageous once in operation in terms of economy, sovereignty and services rendered … “, concludes E.Abonneau.

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