Over the past quarter century, several generations have been replaced not only in our society. Today, new generation nuclear power plants are being built. The latest Russian power units are now equipped with only generation 3+ water-cooled reactors. Reactors of this type can be without exaggeration called the safest. Over the entire period of operation of VVER reactors (water-to-water power reactor), there was not a single serious accident. A new type of nuclear power plant in the world in total has already more than 1000 years of stable and trouble-free operation.
The design and operation of the latest reactor 3+
Uranium fuel in the reactor is enclosed in zirconium tubes, the so-called fuel elements, or fuel elements. They constitute the reactive zone of the reactor itself. When the absorption rods are removed from this zone, the flow of neutron particles increases in the reactor, and then a self-sustaining fission chain reaction begins. With this connection of uranium, large energy is released, which heats the fuel elements. A nuclear power plant equipped with VVER operates on a dual-circuit basis. First, pure water passes through the reactor, which was supplied already purified from various impurities. Then it passes directly through the core, where it cools and washes the fuel elements. Such water is heated, its temperature reaches 320 degrees Celsius, so that it remains in a liquid state, it is necessary to keep it under pressure of 160 atmospheres! Then hot water follows to the steam generator, giving up heat. And the liquid of the second circuit then again penetrates the reactor.
The following actions are in accordance with the usual CHP. The water in the second circuit in the steam generator naturally turns into steam, the gaseous state of the water rotates the turbine. This mechanism makes the electric generator generate electric current. The reactor itself and the steam generator are located inside a sealed concrete shell. In the steam generator, the first circuit water leaving the reactor does not in any way interact with the liquid from the second circuit going to the turbine. This scheme of the placement of the reactor and the steam generator excludes the penetration of radiation waste outside the reactor hall of the station.
About saving money
A new NPP in Russia requires 40% of the total cost of the plant itself for the cost of safety systems. The main share of funds is laid on the automation and design of the power unit, as well as on the equipment of security systems.
The principle of defense in depth based on the use of a system of four physical barriers preventing the release of radioactive substances is the basis for ensuring safety in a new generation of nuclear power plants.
First barrier
It is presented in the form of the strength of the tablets themselves with uranium fuel. After the so-called sintering process in a furnace at a temperature of 1200 degrees, the tablets acquire high-strength dynamic properties. They are not destroyed by exposure to high temperatures. They are placed in zirconium tubes forming the shell of the fuel elements. More than 200 tablets are automatically introduced into one such fuel element. When they fill the zirconium tube completely, the automatic machine introduces a spring, which presses them to failure. Then the machine pumps out air, and then completely seals it.
Second barrier
Represents the tightness of the shell of zirconium fuel elements. The fuel element shell is made of zirconium of nuclear purity. It has increased corrosion resistance, is able to maintain shape at a temperature of more than 1000 degrees. Quality control of the manufacture of nuclear fuel is carried out at all stages of its production. As a result of multistage quality checks, the possibility of depressurization of fuel elements is extremely low.
Third barrier
It is made in the form of a strong steel reactor vessel, the thickness of which is 20 cm. It is designed for a working pressure of 160 atmospheres. The reactor vessel prevents the release of fission products under the protective shell.
Fourth barrier
This is a sealed protective shell of the reactor hall itself, which has another name - containment. It consists of only two parts: the inner and outer shell. The outer shell provides protection against all external influences, both natural and man-made. The thickness of the outer shell is 80 cm of high-strength concrete.
The inner shell with a thickness of concrete wall is 1 meter 20 cm. It is covered with a solid steel 8 mm sheet. In addition, its cable ties are reinforced by special systems of cables stretched inside the shell itself. In other words, it is a cocoon made of steel, which compresses concrete, increasing its strength by three times.
The nuances of the protective coating
The new generation’s internal containment can withstand pressure of 7 kilograms per square centimeter, as well as high temperatures of up to 200 degrees Celsius.
Between the inner and outer shells there is an intershell space. It has a system for filtering gases that come from the reactor compartment. The most powerful reinforced concrete shell maintains integrity during an earthquake of 8 points. It withstands the crash of an aircraft weighing up to 200 tons, and also can withstand extreme external influences such as tornadoes and hurricanes at a maximum wind speed of 56 meters per second, the probability of which is possible once every 10,000 years. And yet such a shell protects against an air shock wave with a front pressure of up to 30 kPa.
Feature of Generation 3+ NPPs
A system of four physical defense in depth barriers eliminates radioactive releases outside the unit in case of emergency. All VVER reactors have passive and active safety systems, the combination of which guarantees the solution of three main tasks that arise in an emergency:
- stopping and stopping nuclear reactions;
- ensuring constant heat removal from nuclear fuel and the power unit itself;
- preventing radionuclides from leaving contamination in case of emergency.
VVER-1200 in Russia and the world
Japan’s new generation nuclear power plants became safe after the accident at the Fukushima-1 nuclear power plant. The Japanese then decided to no longer receive energy with the help of a peaceful atom. However, the new government returned to nuclear power, as the country's economy suffered heavy losses. Domestic engineers with nuclear physicists began to develop a safe new generation nuclear power plant. In 2006, the world learned about a new heavy-duty and safe development of domestic scientists.
In May 2016, a grandiose construction in the chernozem region was completed and the successful completion of testing of the 6th power unit at the Novovoronezh NPP. The new system works stably and efficiently! For the first time during the construction of the station, engineers designed only one and the highest cooling tower in the world for cooling water. While previously built two cooling towers for one power unit. Thanks to such developments, it was possible to save financial resources and save technology. Another year at the station will be carried out work of a different nature. This is necessary in order to gradually put into operation the remaining equipment, since it is impossible to start everything all at once. Ahead of Novovoronezh NPP is the construction of the 7th power unit, it will last another two years. After that, Voronezh will become the only region that has implemented such a large-scale project. Voronezh is visited annually by various delegations studying the operation of a nuclear power plant. This domestic development has left behind the West and East in the energy sector. Today, various states want to introduce, and some are already using such nuclear power plants.
A new generation of reactors is working for the good of China in Tianwan. Today, such stations are being built in India, Belarus, and the Baltic states. VVER-1200 is being introduced in the Russian Federation in Voronezh, Leningrad Oblast. The plans are to erect a similar structure in the energy sector in the Republic of Bangladesh and the Turkish state. In March 2017, it became known that the Czech Republic was actively cooperating with Rosatom to build the same station on its land. In Russia, they plan to build nuclear power plants (new generation) in Seversk (Tomsk Region), Nizhny Novgorod and Kursk.