In 2000, Kirk Sorensen was an engineer at the National Aeronautics and Space Administration of the United States. Looking for an alternative method to provide nuclear power for the future gregarious moon, he stumbled upon a book describing a molten salt reactor that used liquid nuclear fuel as a source of energy.
This sounds a bit weird. As far as he knows, all nuclear reactors are fueled with solid uranium. The original "light water" reactors are currently the mainstream in the nuclear energy industry. However, the book explains that the Oak Ridge National Laboratory in Tennessee, USA, has conducted research on molten salt reactors for more than 30 years. Moreover, liquid uranium (ie, thorium-containing fuel) has a unique advantage. For example, even if a catastrophic nuclear reactor core melts, the molten salt reactor will not be affected, and nuclear waste with plutonium and other long-lived radioactive isotopes will not be produced, and those isotopes will be completely destroyed.
Sorensen was puzzled. "Almost all molten salt solutions to nuclear problems are far better than light water reactors. So why not take this approach from the beginning?"
Change is coming soon
In the past decade, many people have been asking this question, not just about molten salt reactors. Due to the war, molten salt reactors are only one of the many alternative technologies that are stranded in the first wave of nuclear commercialization. Other technologies include “fast†reactors capable of burning nuclear waste, as well as industrial carbon-free heating high-temperature reactors that significantly reduce greenhouse gas emissions.
On the whole, these alternative technologies can make up for most, if not all, nuclear power deficiencies. For decades, because the schedule and funding levels are constantly changing, researchers’ attention to these technologies has been intermittent.
The change may be coming soon. Over the past decade, the demand for safe, carbon-free energy in some countries has inspired the government’s interest in alternative nuclear energy technologies. Companies are also working hard to restart and promote some nuclear energy designs. Especially in China and other rapidly developing countries. Optimists believe that even if a disaster at the Fukushima Daiichi nuclear power plant took place last year, it will eventually push people to choose safer nuclear reactors.
Last year, Sorensen founded the Welfare Energy Company in Huntsville, Ala., to promote the commercialization of molten salt reactors. Whether it is a start-up company like Welfare Energy or an industrial giant such as General Electric Hitachi Nuclear, which is using rapid reactors for developers, both large and small companies hope to be ready.
However, revitalizing these technologies is not a success. Although the basic design was completed several decades ago, engineers must also carry out various developments such as the development of radiation protection materials, more efficient heat exchangers, and improved safety systems. Then they must prove to the regulator that all of these security systems work.
However, relevant parties are convinced that the best prospect for the future nuclear industry is to return to the past. Just as Sorensen pointed out that the Molten Salt Project was canceled: "No one ever said, 'We may have been wrong. Maybe we should go back and review the decision.'"
The advantages of molten salt reactors
One of the advantages of solid-reactor fuels is their predictable geometry, and a major disadvantage is the complexity of such reactors. From the intensity of neutron bombardment, the distribution of nuclear fission products to the radiation damage of the fuel crystal structure, everything changes. This has always been a headache for designers, because it is trying to ensure that the reactor can run stably, and trying to convince the debugger that even in the most critical moments, no part of the fuel is allowed to break into critical mass. But when the fuel turns into a liquid, all the problems can be solved. This is also the main reason why the United States developed the molten salt reactor as early as in the 1960s.
As a nuclear fuel, "molten salt" usually refers to uranium tetrafluoride. The liquid state at the operating temperature is mixed with fluorine lithium helium to become a mixture of lithium fluoride and cesium fluoride, uranium tetrafluoride. It acts as a coolant. "It's like a cauldron that doesn't make a sound - it's huge," said Forsberg. "You throw the fuel in and mix it together, but all the ingredients don't change at all."
Sorensen said that liquid fuels also have a big advantage. "If the fuel is not completely consumed, it does not have to be removed from the reactor." Instead, the fuel is recycled through an external recycling device, continuously extracting nuclear fission products and ensuring the fuel. Safe and sound.
Finally, the molten salt design can be applied to a variety of fuels, from conventional uranium to raw nuclear waste or thorium. The reserve of earthworms is probably three times more than that of uranium.
Need new nuclear plant
For all this, reviving molten salt reactors after 40 years of silence is a daunting task. Sorensen said: "We must rebuild a knowledge base that has basically disappeared completely."
In September 2011, Forbes Bay, Peterson, Hu Linwen of the Massachusetts Institute of Technology and Todd Allen, nuclear engineer at the University of Wisconsin-Madison, participated in a three-year US Department of Energy funded nuclear research project. This project took another step forward on the road to the molten salt reactor: the FliBe cooled high-temperature reactor.
Peterson said: "No one has built a salt-cooled solid fuel reactor." If the project is operational, the reactor core will be 4 to 5 times smaller than other designs. Due to the good stability of the salt, the temperature of this reactor is always several hundred degrees lower than the temperature of the destruction limit.
Peterson said that although "it is estimated that it will consume a lot of resources," the company will still build a reactor for testing in the next decade. This is a bold idea. Due to the financial crisis, the financing of all advanced nuclear reactors has been much more difficult since then. In addition, Koladini pointed out that the United States suddenly discovered abundant shale gas. He believes that "in the United States, cheap fossil fuels have caused the construction of some clean energy projects to be postponed, not limited to nuclear energy projects."
In Virginia, there are many unknown factors in the molten salt reactor, but it is worth developing.
However, will nuclear energy really develop further? In fact, people in the industry saw the reason for optimism. In particular, they believe that if climate change causes more and more obvious consequences, it will force the government to set carbon prices. Genia said that even the nuclear disaster in Fukushima may stimulate new nuclear energy technology development. "But it does cause people panic and is more concerned about the safety of nuclear power." However, because people see more clearly, "they will say, hello, these are old factories that have been built for 30 years." At that time, smart new nuclear plants would look much more attractive. (Article from "Nature" Translator: Simei)
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