For more than a month, a total of twelve tons of liquid salt flowed through the pipes of the nuclear power start-up Kairos Power in Albuquerque, New Mexico. The company is working on a new type of nuclear reactor that will be cooled with a molten salt mixture. His first large-scale test cooling system exceeded the 1,000 operating hour mark at the beginning of January. This is the second important milestone for Kairos in recent weeks. In December, the US nuclear regulator Nuclear Regulatory Commission (NRC) issued a construction permit for the company’s first test reactor.
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Nuclear power could provide a steady source of carbon-free energy, critical to combating climate change. At the UN climate conference in Dubai last December, 20 heads of state and government spoke out in favor of tripling the capacity of all nuclear power plants in operation worldwide by 2050. But the technology is, firstly, controversial for environmental and safety reasons and, secondly, new buildings have so far been expensive. Recent major nuclear power projects have been plagued by delays and skyrocketing construction costs. Kairos and other young companies working on improved reactor designs hope to change that – by introducing a new version of nuclear power that could reduce costs and construction times.
“Our technology and design approach are fundamentally different from current commercial reactors,” says Edward Blandford, co-founder and chief technology officer of Kairos. Today, almost all commercial nuclear power plants use the same type of enriched uranium as fuel to generate electricity through nuclear fission and steam generation in turbines. The temperature is controlled with a cooling system that uses water.
However, a growing number of companies are working to optimize this formula to improve costs and also safety. In the case of Kairos, the company plans to use an alternative fuel called TRISO (Tristuctural-isotropic fuel), which consists of tiny uranium-containing particles that can be embedded in graphite shells. TRISO nuclear fuel is robust and can withstand high temperatures, radiation and corrosion. Additionally, the cooling system of a TRISO reactor uses liquid salt instead of water.
Less pressure in the reactor
This could be a big help in making nuclear power plants safer, says Kairos CTO Blandford. The cooling system in water-cooled reactors must be kept under high pressure to prevent the water from boiling – which would leave the reactor without coolant and risk it overheating and spiraling out of control. It is technically possible to boil salt, but this could only happen at very high temperatures. Therefore, these high pressures as in pressurized water reactors are unnecessary.
Molten Salt Reactors were first developed in the 1950s and tested in the 1960s, but were largely shelved as the industry moved to water-cooled designs. “Now that the need for low-carbon energy is growing, there is renewed interest in these technologies,” says Jessica Lovering, co-founder and executive director of the Good Energy Collective, a research organization that advocates for the use of nuclear energy. New technologies could help alleviate some of the safety concerns about water-cooled reactors. They can also generate electricity more efficiently.
The molten salt reactor has been greatly improved over the past seven decades. At the same time, such a system never went into commercial operation. A lot of testing still needs to be carried out before this type of cooling system can be used in nuclear technology, which is closely monitored by the authorities. This is where the Kairos test facility comes into play. It is the world‘s largest system built to circulate FLiBe, a fluoride-based coolant.
The system uses electrical heating elements to simulate the large heat that would be generated during nuclear reactions in the finished reactor. The tests involve pumping a FLiBe mixture through a cooling loop while engineers monitor the temperature throughout the system as well as the purity level of the salt. The company has also tested how the reactor can be refilled and how the power coming out of the system should be monitored and adjusted.
Step by step to the new reactor
Building a complete cooling system that will never be used in a nuclear reactor is a significant investment of time, money and resources. But the approach of taking small steps could help Kairos to successfully introduce the procedure. But that is a historically difficult task, says Patrick White, research director at the Nuclear Innovation Alliance, a nuclear power think tank.
“One of the challenges with nuclear power is that the first step is usually to design the reactor on paper. Next, you have to build the whole thing,” says White. Kairos is now trying to take a different approach and test components during construction to speed up development and avoid getting stuck in a late phase of construction.
Kairos is also making progress in the development of an overall facility. In December, the company received approval from the NRC to build Hermes-1, its first test reactor. Hermes-1 will generate around 35 megawatts of thermal power – today’s commercial reactors typically generate around 1,000 megawatts of electricity with correspondingly higher thermal power. Completion is scheduled for 2026. Several other companies also use liquid salt or TRISO fuel in their modern reactor designs. Maryland-based X-energy is developing a gas-cooled reactor that uses TRISO fuel – and TerraPower and GE Hitachi Nuclear Energy are developing a sodium-cooled reactor that also uses molten salt for energy storage.
There is still a long way to go for Kairos and other companies. The company plans to build at least two more large test cooling systems before assembling the parts for Hermes-1, says engineering chief Blandford. The company must also obtain an operating license for Hermes-1 – the second of two steps it must go through with the NRC. Next is Hermes-2, which will include two reactors of similar size and design to Hermes-1, as well as a system to convert the heat generated into electricity. Eventually, the company will move to larger, commercial reactors. All of this will take time, but Kairos and its competitors are convinced that the result will be worth it. “Our technology is unique,” says Blandford, “and it opens up unique opportunities to go into areas that other technologies cannot.”
(jl)
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