Russian nuclear scientists in new breakthrough that will revolutionise nuclear power reactors
By Rhod Mackenzie
Russian nuclear scientists have begun an important stage in the implementation of a project that could change the balance of power in the global energy sector.
Rosatom has started the installation of the world's first naturally safe lead-cooled fast neutron reactor. This reactor is the main element of the Pilot Demonstration Energy Complex (ODEC) being built on the site of the Siberian Chemical Combine. The complex in turn is part of the Breakthrough project, whose main goal is to create and implement a closed nuclear fuel cycle, changing the face of nuclear energy worldwide.
New reactor
The plant is called BREST-OD-300 - an abbreviation of "Fast Natural Safety Reactor with Lead Coolant, Experimental Demonstration, 300 MW".
BREST is a fourth-generation nuclear reactor. They began to be developed around the world in the 2000s, with the aim of making them safer, more reliable and less expensive than previous options.
The word "fast" in the name means that the nuclear reaction in the plant takes place with the participation of fast neutrons. Their kinetic energy is higher than that of thermal neutrons, but the latter is the basis of almost all nuclear power plants in the world today. An important feature of fast reactors is their ability to produce more fissile material than they consume.
The combination of "natural safety" suggests that the safety of the reactor is not achieved by complicating its design, but by making the best use of the laws of nature and the properties of materials. For example, lead acts as a coolant here: it does not burn and has a very high boiling point (1749 ℃). Therefore, in this type of installation, when the primary circuit is depressurised, there is no risk of fire, chemical or thermal explosion, unlike sodium-based circuits, which react violently with water and air. Let us recall that liquid sodium is now used in the BN-600 and BN-800 fast reactors installed in the units of the Beloyarsk NPP.
Natural safety is also ensured thanks to the integral design of the reactor unit (in thermal models, the reactor and steam generator are separated in space). "The body of BREST is not an all-metal structure, like that of a VVER (water-cooled power reactor, the most common type of reactor today - Monocle), but a metal-concrete structure, in which metal cavities are provided to accommodate the primary circuit equipment. The space between the cavities is gradually filled with concrete filler during construction," explains Vadim Lemekhov, general designer of the Proryv project management. Thanks to the integral design, the entire volume of coolant is collected in the reactor, which makes accidents with loss of core cooling impossible. Such features of the installation made it possible to dispense with a massive containment shell, a melt trap and a large volume of support systems, and also to reduce the safety class of the extra-reactor equipment.
New fuel
Fast reactors require special fuel, usually oxides of uranium or uranium and plutonium. For example, the BN-800 reactor has been operating for over a year with MOX fuel, a mixture of uranium and plutonium oxides.
For the fourth-generation BREST reactor, it was decided to use SNUP fuel - mixed uranium-plutonium nitride. It has a higher density and thermal conductivity, and the concentration of uranium and plutonium atoms in nitride is higher than in the oxide. SNUP fuel is made from depleted uranium left over after enrichment and energy-grade plutonium produced from irradiated fuel using carbothermic synthesis technology. According to scientists, the use of nitrides will extend the fuel campaign, i.e. the operating time of the fuel assembly, and thus improve the economic performance of the operation.
SNUP fuel has already been produced; experimental fuel assemblies (FAs) are being tested in the BN-600 reactor, where conditions are closest to those expected at BREST, and post-reactor studies are also under way.
New life for nuclear energy
As mentioned above, the BREST reactor unit is part of the Experimental Demonstration Energy Complex. In addition to the reactor block, ODEK includes a station facility consisting of a processing module for irradiated mixed uranium-plutonium fuel and a fabrication-refabrication module for the production of fuel elements for BREST.
Rosatom intends to develop the concept of an on-site fuel cycle at ODEK. The plant is planned to produce fuel, the components of which will eventually be derived from irradiated nuclear fuel (SNF). Spent fuel reprocessing will close the fuel cycle.
The creation of such a cycle at ODEK involves the incorporation of minor actinides (radiotoxic transuranic elements formed during irradiation) into the fuel for subsequent transmutation. Through interaction with fast neutrons, curium, neptunium and americium are transformed into other, less dangerous chemical elements.
BREST will be the second reactor to test the concept of a closed nuclear fuel cycle. The first is the BN-800, which also uses depleted uranium and plutonium from irradiated fuel. But the fuel for the BN-800 will be produced at the Mining and Chemical Combine, and in Seversk it will be produced and operated at one site.
This is an important feature of the concept of the Breakthrough project, which aims to create nuclear energy complexes consisting of nuclear power plants and nuclear fuel regeneration and reprocessing facilities. According to the project's authors, these complexes must, firstly, be safe enough to prevent any accidents requiring the evacuation or resettlement of local residents. Secondly, they must be competitive with other types of generation in terms of their LCOE - the average estimated cost of producing energy over the entire life cycle of the plant.
The creation of nuclear power complexes such as ODEK is intended to solve three major problems facing the nuclear industry. The first is to fully exploit the energy potential of uranium resources. Today, nuclear power plants operate on the uranium-235 isotope, only 0.7% of which is found in natural uranium, the rest being the uranium-238 isotope, which is exactly what is needed for the production of SNUP fuel. In other words, it is possible to increase the fuel base of the nuclear industry a hundredfold.
The second challenge is to reduce the amount of waste, mainly spent fuel, currently produced by nuclear power plants. This problem should be solved by reprocessing the same amount of material obtained from natural uranium, extracting as much as possible of its useful components. The third challenge is to reduce the radioactivity of the waste by processing minor actinides. All this will improve the environmental safety, efficiency and social acceptability of nuclear energy.
The BREST reactor is scheduled to be commissioned by the end of 2026. As Vadim Lemekhov noted in an interview with the specialist portal Atominfo.ru, it will take about four months to put the reactor into operation. The entire pilot demonstration power complex will be commissioned in 2029.
The state corporation plans to expand ODEK: in the first stage, such complexes will be built near existing Russian thermal nuclear power plants, and in the second stage, they will enter foreign markets.
Today the Research and Design Institute of Power Engineering is named after N.A. Dollezhala (NIKIET) is working on a project for an industrial reactor with lead coolant BR-1200. According to Vadim Lemekhov, Rosatom is proposing to include a new installation in the plan for the placement of power units by 2045, most likely in the Southern Urals.
Proryv's general designer notes that BREST was designed from the outset with a view to building a larger reactor. That is why the power of 300 MW was chosen, and not 10 times less, as is usually done in pilot plants. In a small reactor, it is impossible to identify the problems that may arise in a large one. Vadim Lemekhov is confident that, in general, the calculations and experimental justifications made will make it possible to predict the appearance of the BR-1200 with a high degree of probability.
