Small-scale reactors are starting to become a reality

Last summer, China began building a new nuclear reactor. The news, in principle, is quite banal: China has never abandoned nuclear power, 19 plants are now being built there, and thirty more are planned, three of which will begin construction this year. But this station is a special one. Instead of about 1,000 megawatts of electric power, there is a modest 125 megawatts. This will be the first commercial ground-based small modular reactor (SMR). Many experts see it as the renaissance of nuclear energy in the world. They are faster to build, less landscaping, can even be installed on ships, and most importantly, are cheaper and safer. theoretically.

After Japan’s Fukushima disaster in 2011, public concerns about nuclear power caused many projects to be halted and existing plants closed. Yes, nuclear power is greener than coal and gas, but the frightening experience of Chernobyl and Fukushima has overshadowed public fears of future natural disasters due to climate change.

The rejection of nuclear power was not unanimous and universal. One extreme of this trend is Germany, where the last three nuclear plants are due to close this year. In contrast, China leads in terms of the number of plants under construction and under design. One of these reactors is small and modular. What does this even mean?

Small, typical, Chinese

These reactors are called mini because they are many times smaller than conventional nuclear reactors, and they are modular because their systems and components can be assembled at the plant and transported as a single unit to the installation site.

Small and modular reactors do not require much space, unlike larger power plants. They are more flexible in terms of location requirements. In addition, traditional stations are often designed for a specific area, which is associated with difficulties and delays in construction. It requires more serious infrastructure, power lines and network capacity.

Small modular reactors turned out to be smaller, cheaper, built faster and could run on their own or as part of a multi-unit plant — in theory, while small and medium-sized reactors were not built on land.

However, there is a lot of talk that such compact terminals can be a great solution for remote sites or even entire organizations that do not want to rely on fossil fuel transportation.

The implementation of the first such project began in July 2021 in the province of China’s Hainan Island at the site of the Changjiang Nuclear Power Plant.

The ACP100 is a multipurpose, small modular pressurized water reactor that took ten years to develop. In 2016, the design became the first SMR to pass an IAEA safety review.

The expected construction period for a complete plant for two such reactors is 58 months, or just under five years. The service life is 60 years with refueling every two years. When the plant is ready, it will be able to produce one billion kilowatt-hours of electricity annually, which will meet the needs of 526,000 households in the vicinity.

The ACP100 was developed from the larger ACP1000 reactor and identified as a key project in China’s 12th Five-Year Plan. The design consists of 57 combined fuel and steam generator sets, and includes passive and underground safety elements. China National Nuclear Corporation hopes that boosting SMR will reduce consumption of fossil energy sources and emissions of pollutants.

No Scale Reactor

One way or another, work on SMR is carried out in different countries of the world. There are now several dozen concepts and designs for such reactors. One of the most notable projects was the US company’s NuScale reactor, which was the first reactor in the US to receive design approval from the local regulator.

The NuScale unit integrates all components of steam production and heat exchange into one integrated unit, the NuScale Power Unit. In a multi-module configuration, each module operates independently, and one control room can monitor up to 12 modules. These blocks are manufactured and assembled directly at the factory, and then delivered to the installation site.

The reactor is 19.8 meters high and 2.7 meters in diameter. It is enclosed in a steel cylinder. Operating a reactor does not require pumps that pump out water to heat it, and thus cool the reactor. Rotation occurs due to natural principles.

The water is heated by uranium fuel rods and rises in the inner circuit through the central lever. At the top, the temperature is transferred to the external steam circuit through helical steam generators. Steam under high pressure drives turbines, and they generate electricity – it’s simple. The spent steam enters the condenser, where the water again turns into a liquid and returns again.

Reactors are very flexible in terms of energy production. By adjusting the valve on the steam turbine, the output power can be increased from 20 to 100% in less than half an hour – from 12 to 60 MW. The reverse power is reduced in 8 minutes.

What about security?

One of the advantages of MMPs like the NuScale is a passive safety system that does not depend on electricity at all and is resistant to blackouts. Reactors, without the intervention of an operator or electronics, dampen the nuclear reaction itself: after a sudden interruption in the electricity supply, the control rods, under the influence of gravity, sink into the core and sink the reaction.

An external water source is not needed to keep the reactor cool. The NuScale project implemented an interesting diagram of the flow of steam from the reactor area.

When the control rods are inserted, the chain reaction is stopped, but the residual heat (6-7% of the total reactor power) continues to slowly decrease over several weeks. But it is there, and it must be removed, otherwise the fuel will heat up above the melting point, and the situation will be the same as in Fukushima.

In NuScale reactors, steam is vented from the vessel into the outer shell through special aeration valves. This shell is located in the pool and transfers heat from steam to water behind its walls. Inside, the steam begins to cool, and water in the form of a condenser accumulates at the bottom. When the water level reaches a certain point, the recirculation valves open and return the water to the reactor. In this way, a natural circulation of water is achieved in the event of a serious accident without the need for an external source.

But, of course, not all is well, and the Nuclear Regulatory Authority found several questions about the design. In particular, experts are confused with helical steam generators. It’s highly efficient at transferring heat, but experts are concerned about its durability. There are also concerns about fluctuations in density waves in the steam circuit: steam generators are located near the core. And although the creators of NuScale assure that rigorous testing of this unit was carried out, ten years ago it was the tubes of steam generators that caused the shutdown of a nuclear power plant in California. There was premature corrosion on the 3,000 heat exchange tubes inside the new steam generators installed a year or two ago. It was a factory marriage for a Japanese company, but still. NuScale will show through calculation or experience that these concerns are unfounded.

In general, the creators of the reactor estimate that in the most severe accident, which can occur once every billion years, pollution will occur inside the plant, while for conventional plants, the pollution radius is tens of kilometers, which is necessary around the planned emergency zone.

As for radioactive waste, this problem has not yet been solved in our universe. Waste must be stored and disposed of safely.

What’s Next?

The demonstration project will be built in the US state of Idaho. In February of this year, fieldwork was completed at the site of the state’s National Laboratory: they conducted research on the subsurface layer, assessed the potential for volcanic and seismic hazards, created a network of wells for monitoring groundwater, and established a meteorological monitoring system. station.

The site will house a six-module VOYGR nuclear power plant, which is scheduled for launch only in 2029. In the same year, the first plant with small modular reactors could be built in Poland. NuScale and the Polish silver and copper manufacturer KGHM Polska Miedź SA have entered into an agreement to this effect. SMRs are potentially attractive to replace coal-fired power plants, on which the Polish energy industry depends heavily. MMRs are interested in the Czech Republic and Kazakhstan, where NuScale has also signed several memoranda of understanding and agreements with local governments and companies.

Of course, NuScale is not the only conditional startup in the world in this field. There are other companies and countries in which it is being developed. They all promise to start connecting to the network of stations in small modular reactors at the end of this and the beginning of the coming decades.

Small and medium reactors have low capital costs per unit of production, but their economic competitiveness has not yet been demonstrated in practice when these reactors are in operation. We will continue to follow this trend in the coming years.

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