Molten salt reactors could save nuclear energy

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Molten salt reactors, a type of nuclear reactor first explored in the 1950s, could be the future of clean energy – if we can overcome the problems that have held them back for more than half a century .

Fission 101

Nuclear fission occurs when a neutron hits the nucleus of an atom, splitting the atom. This releases a tremendous amount of energy, along with extra neutrons which can then split more atoms, creating a self-sustaining fission reaction.

Nuclear reactors control the fission process so that the energy, released as heat, can be used to boil water, creating steam that can spin electricity-generating turbines.

The process creates no carbon emissions and can take place whether the sun is shining or the wind is blowing, making nuclear power a potentially important ingredient for a clean energy future.

It takes about 7 years and 10 billion dollars to build a nuclear power plant like the ones we already have.

However, today, nuclear represents only 10.3% of the world’s electricity production, and the number of reactor closures exceeds the number of constructions.

This is partly because it takes about 7 years and $10 billion to build a new nuclear power plant like the ones we already have, and some potential operators are hesitant to make such a large investment, especially when the electricity from natural gas and renewable energies are becoming cheaper.

At the same time, many potential constructions are pushed back by a public concerned about the possibility of a nuclear disaster, such as Chernoby or Fukishima, despite the fact that nuclear energy is historically much safer than coal or natural gas.

Molten salt reactors

To increase the amount of electricity generated by nuclear fission, we may need to rethink how we harness it.

In most nuclear power plants today, water is pumped under high pressure to the reactor core where fuel pellets enclosed in metal rods undergo fission. This heats the water to around 600 F, but the high pressure prevents the water from boiling.

The super hot liquid water is then pumped into a chamber containing more water. Its heat causes this water to boil, creating the steam needed to turn the turbines. The cooler water then returns to the fuel chamber to be reheated so the cycle can continue.

The high pressure needed to keep the super hot water in liquid form increases the likelihood of a leak, and if any water escapes, the fuel can overheat, melt the containment rods and potentially release radioactive material into water and the environment.

To avoid this, reactors require many back-up systems and redundancies, which further increases their cost and complexity.

Molten salt reactors are expected to be cheaper to build and even more reliable than today’s nuclear power plants.

This design isn’t our only option, though.

In the 1950s, American researchers began to explore the concept of molten salt reactors, which use molten salt – salt that is solid at room temperature but liquid at high temperatures – instead of water as the heat transfer material. heat and keeping the fuel at a stable level. Temperature.

The type of salt proposed for these reactors remains liquid at temperatures as high as 2,500 F – without any pressurization. This higher temperature would increase reactor efficiency and generate more electricity, while the lack of pressurization would reduce the risk of leakage.

Nuclear fuel cannot melt if it is already liquid.

Instead of solid fuel rods, separate from the heat-carrying water, some molten salt reactor designs require the fuel to be dissolved in the molten salt itself.

This eliminates the risk of melting – the fuel cannot melt if it is already liquid – and if there were a leak, any salt and fuel that escaped would quickly solidify into rock as it cooled. This would be easier to clean than the water or radioactive steam released in the event of a leak from a pressurized water reactor.

Molten salt reactor designs also include a safety feature called a “freeze valve” or “freeze plug”. This plug separates the molten salt mixture above from a holding tank below. If the mixture ever gets too hot, the valve melts and the molten salt falls into the tank under the effect of gravity, which stops a disaster even if all the backup systems have failed.

molten salt reactor

An example of solid (left) and molten (right) salt. Credit: Oak Ridge National Laboratory

Although we don’t know for sure what it would cost to build a molten salt reactor, analysts expect it to be cheaper to build than standard water reactors since the design includes fewer parts.

Reactors can also be more reliable – today’s reactors typically have to be taken offline every 18-24 months for refueling, but spent fuel dissolved in molten salt could potentially be processed and new fuel added during that the reactor was operational.

However, the promise of molten salt reactors has yet to be realized.

“Even today, no material can function satisfactorily in the high radiation, high temperature, and corrosive environment inside a molten salt reactor.”

MV Ramana

Researchers at Oak Ridge National Laboratory built the first proof-of-concept molten salt reactor capable of self-sustaining fission, the Molten Salt Reactor Experiment (MSRE), in 1965.

But over the next four years it was unexpectedly shut down 167 times – mostly due to technical issues involving various components – and in 1969 it was shut down permanently.

If these technical problems had not occurred, it is still not known how long the reactor could have survived another problem related to the use of molten salt.

“Even today, no material can function satisfactorily in the high radiation, high temperature and corrosive environment inside a molten salt reactor,” wrote energy and resources expert MV Ramana in the Bulletin of the Atomic Scientists in June 2022.

A new era

No one has operated a molten salt reactor since MSRE closed, but with climate change exacerbating the need for cleaner energy, we are now seeing renewed interest in the design.

Bill Gates’ bet

In February 2022, TerraPower, a nuclear energy company founded by Bill Gates, and Southern Company, a gas and electric utility, announced that they were teaming up to build the Molten Chloride Reactor Experiment. (MCRE) funded by the DOE at the Idaho National Laboratory.

When complete, the MCRE will be the world’s first critical fast spectrum salt reactor – fast reactors are able to sustain fission without using a moderator to slow the neutrons released during the fission process, increasing their efficiency.

Data from the test reactor will inform the development of TerraPower’s Molten Chloride Fast Reactor – the company plans to build a 180 megawatt demonstration of this system in the early 2030s, which would be enough to power around 90,000 homes.

The Chinese thorium reactor

In August 2022, China authorized researchers from the Shanghai Institute of Applied Physics (SINAP) to start up an experimental molten salt reactor, fueled by a mixture of uranium and a much more abundant element, thorium.

“For now, there is enough uranium to power all the reactors in operation,” nuclear reactor specialist Sylvain David told FRANCE 24 in December 2021. “But if the number of reactors increases, we could arrive at a situation where the supply would no longer be sufficient, and the use of thorium can considerably reduce the need for uranium.

While SINAP’s molten salt reactor is only designed to generate enough electricity for around 1,000 homes, if tests go well, China is ready to build a larger version that could power hundreds of thousands. of hearths.

molten salt reactor

A sectional view of the SINAP molten salt reactor. Credit: SINAP

The micro-reactor

In October 2022, researchers at Brigham Young University announced the design of a molten salt reactor that they say is powerful enough to power 1,000 American homes with electricity – and small enough to fit in the bed of a 40 foot truck.

This small size would presumably be much cheaper and simpler to build than a standard nuclear power plant and could facilitate the delivery of nuclear power to remote areas, but there are currently no plans in place to build the one of the reactors.

BYU researcher Matthew Memmott, however, told the Register that his team also developed a method to make the salt less corrosive by removing water and oxygen from it. They have already partnered with the San Rafael Energy Research Center in Utah to build a salt refining center for operators of molten salt reactors, both mini and large.

molten salt reactor

BYU researcher Matthew Memmott working in his lab. Credit: Brooklyn Jarvis Kelson/Photo BYU

Look forward

These are just a few of the many groups that are taking a closer look at molten salt reactors, but even if one or more of their designs are built, we won’t know for some time whether they’ve managed to overcome the corrosion problem that has long held back technology.

“The problem with corrosive products is that you only realize their damage five to ten years later,” said Francesco D’Auriam, a specialist in nuclear reactor technology at the University of Pisa, at FRANCE 24.

If today’s researchers can build a molten salt reactor that resists corrosion and overcomes the technical challenges faced by MSRE, the device could increase the amount of electricity generated by nuclear fission – and bring us closer to a clean energy future.

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