Idaho National Laboratory researchers have demonstrated a surrogate reactor concept that replaces neutron-driven signals with beams of LED light, creating a zero-radiation test environment for reactor monitoring and control. In a February 2026 update shared by INL via Newswise, the lab described using light to stand in for neutron flux so engineers can test instrumentation and control behavior without handling fissile material. The setup can mimic key fission-like operating dynamics for control-system development, though whether light-simulated conditions can fully capture the complexity of real fission physics remains an open question.
LEDs Standing in for Neutrons
The concept is deceptively simple. In a conventional nuclear reactor, neutrons collide with fuel atoms to sustain a chain reaction, releasing enormous heat. That process requires enriched uranium or other fissile material, shielding, and layers of safety systems. INL’s surrogate approach strips the nuclear material out of early-stage testing. Instead of splitting atoms, the device uses LED light to replicate neutron behavior signals inside a reactor-like core environment. The result is a testing platform that mimics fission-like reactor dynamics for sensors and control logic while producing no radioactive byproducts, allowing experiments that would otherwise require nuclear material to be conducted in a more flexible environment.
Think of it as a flight simulator for nuclear engineers. Pilots train for years in simulators before flying real aircraft, not because simulators perfectly reproduce turbulence, but because they replicate the decision-making environment with enough fidelity to build skill and catch design flaws. INL’s LED reactor works on a similar principle. It allows researchers to stress-test reactor control logic and instrument response in a setting that behaves like a reactor core from the standpoint of the control system, without the regulatory and physical constraints that come with handling fissile material. INL’s description emphasizes that, for development testing, hazardous reactor materials can be replaced by a controllable field of light that stands in for neutron flux.
How MARVEL’s Control Systems Fit In
The surrogate reactor is not a standalone curiosity. As described by INL, it connects to the control systems being developed for MARVEL, a microreactor project at the lab. MARVEL is intended to demonstrate how compact nuclear plants could provide reliable power in certain applications. By linking the LED surrogate to MARVEL’s control architecture, INL can validate software, sensor arrays, and automated responses before the fueled reactor operates. This integration means engineers can iterate on control system design faster than if every test required a live nuclear core, turning what used to be rare, high-stakes experiments into more routine lab exercises.
The practical benefit here is speed. Licensing and qualifying a new reactor design in the United States can take years and involves extensive evidence that control systems respond correctly under many scenarios. If parts of that verification work can happen on a surrogate that produces no radiation, the testing cycle could compress. Regulators would still need results from actual fission-based testing before final approvals, but the surrogate can help teams reach those later tests with more mature control logic.
What LED Simulation Cannot Replace
There is a reasonable counterargument that deserves attention. LED light, no matter how precisely calibrated, is not a neutron. Photons and neutrons interact with matter in fundamentally different ways. Neutrons can be absorbed, scattered, or reflected by reactor materials, and those interactions change depending on temperature, fuel composition, and the geometry of the core. An LED array can simulate the output signal of those interactions and feed realistic data to control systems, but it cannot reproduce the underlying physics that generate those signals in the first place. This distinction matters because unexpected reactor behavior can emerge from the physics itself, not only from the control system’s response to it.
This limitation does not invalidate the approach, but it does constrain its usefulness to a specific phase of reactor development. The surrogate excels at testing whether instruments read correctly, whether software responds to simulated anomalies, and whether human operators make sound decisions under pressure. It is far less useful for validating neutronics codes, fuel performance models, or material degradation predictions. Those questions still require either computational simulations benchmarked against real reactor data or, ultimately, actual fission experiments. Treating the LED surrogate as a complete substitute for traditional reactor testing would be a mistake. Treating it as a complement is the more defensible position, especially if project teams are explicit about which questions the light-based simulator can answer and which must be deferred to full-scale nuclear trials.
Implications for Small Modular Reactor Development
The timing of INL’s update aligns with a broader push in the United States to accelerate development of small modular reactors and microreactors. Multiple companies are pursuing licensing and demonstrations, and a common challenge is the time required for testing, validation, and regulatory review to prove that a new design is safe. If surrogate reactors can absorb a meaningful portion of control-system testing, the path from concept to later-stage demonstrations could shorten. Any associated cost savings would depend on the specific program and what testing a surrogate can credibly replace.
The potential reach could extend beyond U.S. borders, particularly for training and non-nuclear testing. A radiation-free surrogate that can be operated without nuclear fuel could make it easier for universities and training centers to run realistic drills in instrumentation and control, though it does not eliminate the eventual need for real reactor experience once a project moves from planning into construction and commissioning.
A Practical Tool, Not a Silver Bullet
The most important thing to understand about INL’s surrogate reactor is what it is designed to do and what it is not. It is a testing instrument for control systems, not a replacement for nuclear reactors. It produces no power, no fission heat, and no radiation. Its value lies in its ability to create a realistic operating environment for the electronics, software, and human teams that will eventually manage real fission plants. That is a narrower achievement than the headline might suggest, but it is also a useful one, especially in an industry where incremental improvements in safety assurance and development speed can have outsized effects on cost and public acceptance.
Nuclear energy development has long been hampered by the fact that many steps of the process involve radioactive material, which can make work slower, more expensive, and more regulated. By carving out a portion of the development cycle and moving it into a non-nuclear domain, INL’s LED-based surrogate offers a way to de-risk certain kinds of innovation before any fuel is loaded. It will not resolve debates over waste disposal, proliferation, or long-term economics, and it cannot answer the most complex physics questions that still demand real reactors. But as a bridge between computer modeling and full-scale fission experiments, this zero-radiation “reactor” can give engineers and regulators a shared, low-consequence sandbox in which to refine the systems that ultimately keep nuclear plants safe.
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*This article was researched with the help of AI, with human editors creating the final content.
