When I sat down with Moto Kinoshita-san, founder of MSLab Inc. and director at Thorium Tech Solution Inc. (TTS), I wasn’t just meeting an engineer. I was meeting a pioneer. A seasoned nuclear scientist with decades of experience, Moto-san has dedicated much of his life to designing and advocating for molten salt reactors (MSRs) a technology he believes could help redefine how we approach clean, safe nuclear energy. Our conversation stretched from the Cold War to climate change, touching on everything from safety valves to geopolitics. He spoke with a calm intensity, often smiling as he recalled experiments from the 1980s, or pausing to find just the right metaphor to help me, a university student, understand.
What stood out most wasn’t just the facts it was his unwavering belief that Japan can lead again, if it dares.
Moto-san began by pointing out something many of us intuitively feel: current nuclear technology feels dated. “Fukushima reminded us that water as a coolant has risks,” he said. Pressurized water reactors operate under high stress; if things go wrong, the results can be catastrophic. Molten salt reactors change that.
These reactors use liquid fuel, often uranium or thorium dissolved in fluoride salt that flows through the core. If overheating occurs, the salt automatically drains by gravity into a freeze-protected tank and solidifies, safely shutting down the reaction. This kind of passive safety eliminates the need for emergency generators or complex operator actions.
“The salt doesn’t boil until 1400°C,” Moto-san added. “It’s stable, and we can design for gravity-driven safety.”
What’s more, MSRs produce less long-lived waste compared to conventional light water reactors. Especially when using thorium, the waste profile changes significantly, producing fewer transuranic elements and offering potential for more efficient recycling. Moto-san also explained how fission products can be continuously removed from the salt, a kind of real-time cleanup that prevents waste from accumulating inside the reactor.
Another unique feature is the flexibility of fuel options. MSRs can use uranium-235, recycled plutonium, or thorium. The thorium cycle breeds uranium-233, which can then be burned in the same reactor, but with caveats.
Moto-san clarified that uranium-233 has not historically been used in nuclear weapons, but it does have proliferation potential. Careful fuel design and international safeguards are essential to ensure peaceful use.
And beyond electricity, MSRs could fuel a range of future applications. With their high operating temperatures and ability to run for years without refueling, Moto-san noted, MSRs could be used for hydrogen or ammonia production, critical elements for clean fuels and fertilizer.
Even when refueling is needed (after, say, a decade), the process is far simpler than with traditional solid-fuel reactors. “You don’t have to open the reactor vessel,” he said. “Liquid fuel allows sealed refueling systems, no need for giant buildings or 10-meter fuel rod lifts.”
As AI, data centers, and electrification grow, the demand for safe, stable baseload power is increasing. MSRs might be the answer.
Alvin Weinberg, despite being the inventor of the pressurized water reactor (PWR), the standard for nuclear power today, understood its fundamental nature and warned about its risks.
Moto-san is closely involved with compact MSR designs such as the mini-FUJI, “RinR” (Reactor-in-Reactor), and the “UNOMI” concepts, which resemble typical Japanese tea cups.
What sets Japan apart, Moto-san said, is its expertise in advanced chemistry, especially its experience in industrialization.
Today, the molten salt landscape is active around the world. In China, the Shanghai Institute of Applied Physics (SINAP) has already built the 2 MW TMSR-LF1 prototype and is aiming to scale up to 10 MW. Canada’s Terrestrial Energy is working on the Integral MSR, designed with commercialization and licensing in mind from the beginning. In the United States, companies like ThorCon, Kairos Power, and TerraPower are advancing MSR technologies using both fluoride and chloride salts.
Japan is also quietly but seriously engaged. TTS and MSLab, the two organizations Moto-san is closely involved with, are focusing on compact MSR designs like the mini-FUJI and “RinR” (Reactor-in-Reactor) concepts. These reactors aim to recycle plutonium and minor actinides, essentially turning nuclear waste into fuel.
Kairos, Moto-san noted, uses solid fuel, which requires opening the core for refueling. Japan’s designs use liquid fuel, allowing sealed, online refuelin, a major operational advantage.
What sets Japan apart, Moto-san said, is its expertise in advanced chemistry. Handling and purifying molten salts requires a unique skill set, and Japan’s researchers from Kyoto, Tohoku, and Kyushu Universities, to CRIEPI and JAEA are leaders in this field. Companies like Toshiba and Hitachi-GE have also explored advanced reactor technologies, though full commercial MSRs are still a few steps away.
“Each country has its strengths. We need cooperation, not duplication,” Moto-san said.
The mini-FUJI, a 25 MWe modular design, reflects this thinking. However, recognizing that the scale of a 25 MWe commercial reactor is too large for a first step, Moto-san is planning to construct a very compact educational demonstration and test reactor instead. This reactor, nicknamed UNOMI after a traditional Japanese teacup, will be the first of its kind built by Japan. The goal of this low-cost project is to demonstrate the extreme safety and high performance of a liquid fuel reactor.
While the concept is compelling, Moto-san was honest about the challenges.
Corrosion is a major hurdle. Salts like FLiBe and FLiNaK use fluorine, which is the strongest chemical bonding agent in the periodic table. This makes the molten salt chemically stable and also why there’s no risk of a hydrogen explosion like at Fukushima. But it also means fluorine can aggressively corrode metals if the redox chemistry is mismanaged.
Instrumentation is also difficult many sensors can’t survive the extreme temperatures and radiation inside a molten salt reactor. “We’re flying blind compared to conventional reactors,” he said.
Another issue is salt solidification. If the salt freezes inside pipes or tanks, restarting the reactor becomes tricky. But this same trait is a safety feature:
“If something goes wrong, we drain the liquid fuel into a tank below the core, where it freezes solid,” Moto-san explained. “That immobilizes radioactive materials and eliminates the risk of pressure build-up.”
And finally, regulation. Most nuclear safety frameworks weren’t written with MSRs in mind. That means developers often face delays and uncertainty while waiting for approval. The cost implications are significant: R&D, custom materials, and licensing hurdles all stack up.
Still, proponents argue that in the long term, MSRs could be cheaper thanks to simplified design, fewer moving parts, and inherent safety.
Moto-san also touched on the geopolitics of nuclear.
While thorium itself is not directly usable as a weapon, the uranium-233 it breeds must be carefully managed. Moto emphasized that technical safeguards such as fuel dilution, continuous denaturing, and international monitoring are critical to preventing misuse.
He noted that most historical nuclear weapons programs, including those in North Korea, India, and Pakista,n used heavy water or other methods, not thorium or U-233-based cycles.
“We’re not just building hardware,” he told me. “We’re building trust. That takes time.”
Despite these obstacles, Moto-san believes Japan can lead in this space. The memory of Fukushima has created a public mandate for safer, smarter nuclear options. And Japan’s research institutions have the capability to turn ideas into reality.
TTS and MSLab are working on plans for demonstration reactors not just in Japan, but potentially in partnership with other countries. Moto-san envisions an international testbed where fuel recycling, safety testing, and transparent operations can all be validated together.
Public skepticism remains a hurdle, but he believes transparency and international collaboration can rebuild trust. Government support, both regulatory and financial, will be crucial. Partnerships with utilities like TEPCO or regional players could also play a role.
“Japan can show the world how to do nuclear safely and wisely. But we must act now.”
MSRs allow us to think in terms of 50-year timelines, or even 100 years, instead of just five. Elements heavier than uranium, which are currently considered waste, could become valuable resources in the near future with the realization of MSR technology. These elements could then be used for energy production, as well as in the creation of medicines and other industrial and everyday products.