If Japan is going to lead in clean energy again, I don’t think it’s going to happen through solar panels or wind turbines, at least not alone. That thought kept coming back to me as I sat in a conference room inside the House of Representatives First Members’ Office Building last week, surrounded by engineers, researchers, and policy veterans. We were all there to talk about something most people in Japan haven’t heard about in decades: molten salt reactors. More specifically, thorium molten salt reactors, compact, safe, low-cost nuclear systems powered by a liquid fuel that most of the world has overlooked, and one that Japan quietly helped pioneer decades ago.
I went into the event, the Nuclear Innovation Seminar, expecting a technical presentation. And sure, there were charts, chemical formulas, and policy timelines. But what struck me wasn’t just the content. It was the mood in the room. There was urgency, yes, but also a sense of possibility. People weren’t there just to critique the past or complain about the slow pace of regulatory reform. They were there because they believed Japan still had a card to play. And they wanted to play it now.
One of the first slides on screen said, bluntly: 「脱炭素できなければ人類は生き残れないよね」, “If we can’t decarbonize, humanity won’t survive.” There was no drama in how it was presented. No one gasped. No one needed to. Everyone knew it was true. It set the tone for everything that followed. This wasn’t a sales pitch. It was a quiet but serious proposal: what if molten salt reactors, something Japan once designed but never commercialized, could be part of the answer?
Most nuclear reactors today use solid uranium fuel rods cooled by high-pressure water. That design is complicated, expensive, and comes with serious risk if things go wrong, as we all remember too well from Fukushima. But molten salt reactors flip that model. They use liquid fuel, molten fluoride salts that carry thorium or uranium as part of their chemical makeup. The system runs at atmospheric pressure. If it overheats, the fuel can simply drain into a holding tank and solidify. No explosion. No steam. No high-pressure meltdown scenario.
This isn’t a new idea. In the 1960s, Alvin Weinberg at Oak Ridge National Laboratory in the U.S. built and ran an experimental molten salt reactor for four years without a single accident. Japan picked up the idea in the 1980s and designed its own version, the FUJI reactor, a small, modular molten salt reactor with safety features built into its chemistry and structure. But then it disappeared from public view. Other nuclear projects took priority, and Japan’s energy policy became more cautious, especially after Fukushima.
Meanwhile, the world moved on. China is building one. The U.S. is funding startups. Even India and Turkey are exploring thorium as a long-term energy resource. What I realized, sitting in that room, was that Japan is in a strange position: we were early, but now we’re behind. The country that helped design the reactor might end up importing it.
That contradiction hung over the event, but it didn’t weigh it down. Instead, it made the case for action even stronger. Japan doesn’t have much fossil fuel. Our renewable energy is limited by geography and infrastructure. Our electricity demand is rising, especially with data centers and AI processing. One of the presenters showed a cost comparison slide: traditional nuclear and fossil fuels run around 10 to 30 yen per kilowatt-hour. Renewables can be unpredictable and expensive to store. Molten salt reactors, in contrast, could deliver stable power around 2 to 5 yen per kilowatt-hour. And they could run continuously, day and night.
Of course, there are challenges. The current regulatory system isn’t built to accommodate molten salt reactors. Licensing, materials classification, waste protocols, none of it fits neatly. There’s also public perception. In Japan, “nuclear” still carries fear, not innovation. That’s fair. But the speakers didn’t shy away from it. They acknowledged the trauma and the skepticism. They argued not for erasing that history, but for building something new out of it, something safer, smaller, and smarter.
One solution they proposed was to launch a Japan–U.S. joint development company. Test the first reactor in the U.S., where regulations are more flexible. Use Japan’s engineering expertise to design and refine the technology. Then secure commercialization rights and bring it home. From there, Japan could offer molten salt reactors to the world, not just as a product, but as a model for what thoughtful, safety-first nuclear innovation can look like.
As a student researcher working with the Anthropocene Institute, I’ve spent a lot of time learning about global energy transition technologies. But this was the first time I felt like I was watching a serious proposal for Japan’s long-term energy future take shape in real time. It wasn’t flashy. There were no big declarations. Just calm, focused, technical ambition.
I watched the man sitting next to me, probably an engineer, maybe in his 50s, take photos of almost every slide. During the break, a group of younger researchers gathered in a corner to sketch out licensing scenarios on a notepad. At the end, a few people stayed behind to ask the speakers how they could get involved. It didn’t feel like an ending. It felt like a beginning.
I walked out of the building with a quiet sense of conviction. This isn’t a miracle solution. Molten salt reactors won’t solve every energy problem. But they deserve a place in the conversation, especially in Japan, where the combination of risk awareness, technical discipline, and a deep desire to do better still runs strong.
That seminar didn’t just teach me about a reactor. It reminded me that innovation doesn’t always look like disruption. Sometimes, it looks like returning to an idea that was ahead of its time and realizing its time might finally be now.