The Dawn of the Nuclear Battery: How Project MARVEL is Solving the World’s Water and Energy Crisis

This is Project MARVEL—the Microreactor Applications Research Validation and EvaLuation project.

Led by the U.S. Department of Energy’s (DOE) Idaho National Laboratory (INL), MARVEL is not just another experiment; it is the first new nuclear reactor to be built at INL in over four decades. More importantly, it is the vanguard of a new era: the age of the liquid-metal microreactor.

Part I: The Genesis of MARVEL

The Microreactor Imperative

Project MARVEL was conceived to break this cycle. It is a DOE-authorized test bed, a rapid-prototyping project designed to be built quickly and cheaply to generate the validation data that private industry desperately needs.

The Return of the TREAT Facility

MARVEL is being constructed inside the Transient Reactor Test (TREAT) Facility at INL. TREAT is hallowed ground in nuclear engineering. Built in the late 1950s, it was designed to subject nuclear fuel to extreme bursts of power to see how it held up under accident conditions.

Part II: The Machine – Inside the Sodium-Potassium Core

To understand why MARVEL is special, one must look under the hood. Unlike the commercial reactors that power our cities, which use water under extreme pressure to cool the fuel, MARVEL uses a liquid metal: a eutectic alloy of sodium and potassium (NaK).

Why Liquid Metal?

Water is a good coolant, but it has a fatal flaw: it boils at $100^\circ$C. To keep it liquid at the $300^\circ$C temperatures needed for power generation, you must pressurize it to over 150 atmospheres. This requires massive, thick steel vessels and complex piping that can withstand explosive pressures.

NaK, on the other hand, is a liquid at room temperature (it looks like mercury but is much lighter) and does not boil until it reaches a scorching $785^\circ$C.

This physical property changes the entire safety paradigm. MARVEL operates at high temperatures (around $500-550^\circ$C) but at near-atmospheric pressure. The reactor vessel doesn't need to be a thick pressure cooker; it can be a simple, thin-walled stainless steel canister. If a leak were to occur, the coolant wouldn't explode into steam; it would simply leak out like oil from an engine.

The Heart of the System: Natural Circulation

The most elegant feature of MARVEL is its reliance on natural circulation.

In a traditional reactor, massive electric pumps force the coolant through the core. If those pumps fail (as they did at Fukushima), the reactor is in trouble. MARVEL has no primary pumps. None.

It relies on simple thermodynamics: hot fluid rises, and cold fluid sinks. As the uranium fuel heats the NaK, the liquid becomes lighter and floats up through the core. It travels to a heat exchanger where it gives up its energy, cools down, becomes heavier, and sinks back to the bottom to start the cycle again.

This "passive safety" system is immutable. You cannot "turn off" gravity. If the reactor loses all electrical power, the coolant keeps circulating naturally, removing decay heat and keeping the core safe indefinitely.

• Thermal Output: 85 kW (roughly equivalent to the engine of a small car).
• Electrical Output: ~20 kW (enough to power a small street or a critical facility).
• Fuel: Uranium-Zirconium Hydride (U-ZrH), a "self-regulating" fuel used in research reactors worldwide (TRIGA type). As this fuel gets hotter, it naturally becomes less efficient at sustaining the chain reaction, acting as an automatic brake on power excursions.
• Coolant Loops: Four independent loops transfer heat from the core to the intermediate stage, ensuring redundancy.

The PCAT Validation

Before loading a single gram of uranium, INL engineers built a full-scale, electrically heated replica of the reactor called the Primary Coolant Apparatus Test (PCAT).

Running throughout 2024 and 2025, PCAT was critical. It proved that the natural circulation concept worked exactly as the computer models predicted. It also led to a crucial design pivot: the original plan to use Stirling engines (pistons driven by heat) for heat removal caused too much vibration. Thanks to PCAT testing, the team swapped to a more stable, radiator-like thermoelectric conversion system for the final design, ensuring the reactor would run whisper-quiet.

Part III: The "Produced Water" Revolution

The partners are Shepherd Power (a subsidiary of the oil and gas giant NOV) and ConocoPhillips. Their goal? To use MARVEL to solve the "produced water" crisis in the Permian Basin.

The Invisible Waste of the Oil Age

For every barrel of oil extracted from the ground in places like West Texas, producers also bring up 4 to 10 barrels of "produced water." This is not fresh water; it is a toxic, salty brine, laden with heavy metals, radioactive isotopes, and chemical residues.

Historically, oil companies have dealt with this water by injecting it back underground into deep disposal wells. But this practice has had unintended consequences. The sheer volume of injected water has lubricated ancient fault lines, causing a dramatic spike in earthquakes in regions that were previously geologically stable.

Regulators are cracking down. Injection limits are being tightened, and costs are skyrocketing. Simultaneously, these same regions are facing historic droughts. We are throwing away billions of gallons of water because it is too expensive to clean, while aquifers run dry.

The Nuclear Desalination Solution

Current desalination technologies, like Reverse Osmosis (RO), are energy hogs. Cleaning produced water—which can be five times saltier than the ocean—requires immense pressure and electricity. Doing this with diesel generators is too expensive and carbon-intensive.

This is where MARVEL steps in.

Nuclear desalination is the "killer app" for microreactors. The MARVEL system provides two things that desalination plants crave:

1. Electricity: To run the high-pressure pumps.
2. High-Grade Waste Heat: This is the secret weapon.

In a standard power plant, 60% of the energy is wasted as heat. MARVEL is designed to capture this heat. By coupling the reactor with a thermal desalination unit (like Multi-Effect Distillation or thermally-enhanced RO), the system can boil or separate the water much more efficiently than electricity alone.

Shepherd Power and ConocoPhillips are targeting a treatment cost of $0.30 to $0.40 per barrel. If they can hit this target, they flip the economic model of the oil industry upside down. Instead of paying to dispose of wastewater, companies could turn a liability into an asset—fresh water for agriculture, hydrogen production, or municipal use.

This pilot program with MARVEL will be the first time in history that a modern microreactor is physically coupled to a produced water treatment facility to validate this synergy.

Part IV: The Regulatory Bridge

One of the most significant, yet invisible, contributions of Project MARVEL is its role as a regulatory icebreaker.

The United States has two pathways for nuclear reactors:

1. NRC Licensing: The rigorous, expensive process for commercial power plants (10 CFR Part 50/52).
2. DOE Authorization: A streamlined process for research reactors located on government sites, overseen by the DOE itself.

MARVEL is a DOE-authorized reactor. This allows INL to move fast and take calculated risks that a commercial startup could not afford. However, the data MARVEL generates is being collected in strict accordance with NRC Quality Assurance standards (NUREG-1537).

This strategy creates a "bridge." Commercial startups like Aalo Atomics (which is developing a larger 20 MW version inspired by MARVEL) can use the data from MARVEL's fuel performance, coolant chemistry, and natural circulation stability to validate their own computer codes.

The Shepherd Power Model

Shepherd Power is particularly interesting because it represents a new kind of nuclear customer. They are not a utility company. They are an industrial service provider. Their business model is "Energy-as-a-Service."

They plan to own and operate fleets of microreactors, deploying them to oil fields, mines, or data centers. The customer (e.g., ConocoPhillips) doesn't buy the reactor; they just buy the heat and water it produces. This model removes the capital risk from the end-user and could be the key to mass adoption.

Part V: Beyond Desalination – The Global Future

While the immediate focus is on Texas oil fields, the implications of MARVEL’s success extend to every corner of the globe.

Water Security in the Global South

Consider the drought-stricken regions of North Africa and the Middle East. Nations like Jordan and Morocco are facing existential water crises. Large coastal desalination plants are energy-intensive and bind these nations to fluctuating fossil fuel prices.

A fleet of MARVEL-style microreactors could be deployed to coastal towns or inland brackish aquifers. Because these reactors are air-transportable and require refueling only once every 10-20 years, they provide energy sovereignty. A nation doesn't need a pipeline or a rail line to keep the power on; once the reactor is delivered, the energy is secured for a decade.

Disaster Relief and Defense

The U.S. military is a key observer of the MARVEL project. The Department of Defense's Project Pele is also developing a mobile microreactor. MARVEL complements this by validating the liquid-metal approach.

Imagine a hurricane strikes a Caribbean island, destroying the grid and contaminating the water supply. Today, we send diesel generators, which require a constant, vulnerable supply chain of fuel ships. In the future, a C-17 transport plane could land with a containerized microreactor. Within days, it could be producing megawatts of power and hundreds of thousands of gallons of clean water, running autonomously for the duration of the recovery.

The "Nuclear Battery" for Data Centers

The MARVEL design—compact, silent, and safe—is perfect for this. The "Shepherd Power" model of owning and operating the reactor on behalf of the customer applies perfectly to Amazon, Google, or Microsoft. The reliability of a NaK-cooled reactor, with its passive heat removal, offers the "five nines" (99.999%) uptime that the tech industry demands.

Part VI: Challenges and The Road Ahead

Despite the optimism, the road for MARVEL is not without potholes.

The fabrication of the MARVEL coolant system by Carolina Fabricators is a success story, but it highlights a weakness. The U.S. supply chain for nuclear-grade components has atrophied. Rebuilding the industrial base to mass-produce these reactors—not just hand-build one test unit—is a monumental task.

MARVEL uses HALEU (High-Assay Low-Enriched Uranium) fuel. Currently, the commercial supply of HALEU is limited, with Russia historically being a major supplier. The U.S. is racing to build domestic enrichment capacity (via companies like Centrus Energy), but ensuring a steady supply for a future fleet of thousands of microreactors remains a strategic bottleneck.