Fuel Breakthrough Paves Way For Cutting-edge Nuclear Reactor

The Idaho National Laboratory (INL) has overcome a major challenge in making a Generation IV nuclear reactor feasible. Using a new process, a team developed a more efficient way of processing fuel for cutting-edge molten salt reactors.

One of the main drives to revive nuclear energy in the 21st century is the development of new reactor designs that, just a few decades ago, were considered experimental, with little prospect of becoming practical.

Molten Salt Reactors: A New Frontier

One of the categories of these Generation IV reactors are molten salt reactors, which replace enriched uranium or plutonium fuel rods and water moderator/coolant with a mixture of nuclear fuel and molten salt. While the concept may seem strange initially, it offers numerous advantages over the commonly used pressurized water reactors.

There are various types of molten salt reactors, but they all share common features.

Firstly, they operate at higher temperatures than conventional reactors and at atmospheric pressure. This makes them more efficient, reduces mechanical stresses, and eliminates the risk of a runaway meltdown, as the nuclear reaction is self-limiting. Moreover, dangerous or harmful gases such as hydrogen and xenon can be easily vented through a simple chemical process.

Operating at around 600°C (1,112°F), molten salt reactors offer 50% greater efficiencyThey continuously recycle their fuel, which reduces nuclear waste, and they can add new fuel while removing waste through essentially plumbing

These reactors are also quite versatile, able to handle various types of fuels, which not only enhances their economic viability but also contributes to reducing nuclear weapons proliferation. Additionally, the reactor designs can be modular, allowing for adaptation to small-scale plants that can serve various industrial applications, including petroleum production, hydrogen generation, desalination, floating power plants, and ship propulsion.

Challenges in Building Molten Salt Reactors

Although this all sounds promising, the question remains: why haven’t engineers built molten salt reactors before? The answer is that scientists have known about these reactors since the very beginning of the nuclear age. In fact, one of the first reactor designs for the Manhattan Project, which aimed to build the first atomic bomb, proposed using a slurry of salt and uranium. However, this design was short-lived because they didn’t have enough uranium available, and the molten salt design couldn’t produce plutonium, so they chose a graphite reactor instead.

Since then, there have been several molten salt projects, including one for submarines and another to power aircraft (fortunately, those did not advance). However, these projects never gained traction because nuclear reactors are much more complex than what school textbooks might suggest.

Despite their advantages, molten salt reactors do have limitations. They are prone to corrosion issues, as well as thermal and neutron stresses. Additionally, the salts strip away protective oxide layers from metal components. Another challenge is fuel reprocessing, which is mechanically simple but complicated by the radioactive nature of the fuel.

Challenges in Nuclear Physics and Materials

Furthermore, basing nuclear reactions on flowing mixtures of hot liquids introduces some areas of nuclear physics that are, in technical terms, still uncertain.There is a lack of standardized computational tools for reactor physics simulations, and researchers have limited understanding of how prolonged operation affects structural materials.

As if that weren’t enough to give a nuclear engineer pause, there’s the issue of fabricating the fuel for the reactor. You can’t use metallic uranium like conventional fuel rods. It must be in a form that dissolves in chloride salts, such as uranium chloride (UCl₃) or uranium tetrachloride (UCl₄), which presents challenges related to fabrication complexity, chemical stability, reactivity, additional chemical processing steps, and corrosion.

This is the issue the INL’s Molten Chloride Reactor Experiment (MCRE) is tackling. Since 2020, Bill Phillips and his technical team have been working to find the right uranium compound and methods to produce it in bulk with 90% efficiency.

Collaborative Effort to Build a Demonstration Reactor

The MCRE, in collaboration with Southern Company and TerraPower, aims to build the world’s first critical fast-spectrum molten salt reactor, with the goal of having a demonstration reactor by 2028 and a commercial version by 2035.

The sticking point is that in 2020, INL could only produce two or three ounces (57 to 85 g) of fuel at a time. Unfortunately, the final reactor needs three and a half tons to reach criticality. So, INL started working with denatured uranium, which is much cheaper but chemically identical to fissionable uranium, to produce more fuel per batch.

After much trial and error, along with a custom prototype furnace and specialized equipment, the team discovered how to combine the right conditions, ingredients, and techniques to produce 18 kg (39 lbs) at a time.

Next Steps for Full-Scale Fuel Production

According to INL, the next step is to produce five more batches by October 2025 to demonstrate the potential for large-scale production of enriched nuclear fuel and to charge the MCRE for its first reactor experiments. These experiments aim to study neutron behavior in the reactor, verify theoretical models for fast-spectrum chloride reactors, measure fuel stability, assess the corrosion resistance of structural materials in chloride salts, and examine radiation damage to containment materials.

We started out wasting too much of the uranium metal we had access to, and we wouldn’t be able to make enough fuel salt for the reactor to go critical,” said Nick Smith, MCRE project director. “After years of experimentation and revisions, we finally found the right process to achieve the perfect yield. It takes a special kind of perseverance to keep working on a problem when there’s no guarantee that you’ll find a solution.

Read the original article on: New Atlas

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