OSAKA - A gauge on the control panel crept upward as students watched closely inside a university nuclear research facility in western Japan.
"0.01 watts. We've reached criticality," one student announced, drawing applause from the group.
About 20 students from Fukui University of Technology were taking part in an August training exercise at Kindai University's Atomic Energy Research Institute in Higashiosaka, Osaka Prefecture, learning how to bring a nuclear fission reaction to a stable critical state.
The Kindai University Reactor, which achieved initial criticality in 1961 as Japan's first reactor built for educational purposes, is now one of only two such university reactors left in the country -- and the only one currently operating.
Its maximum thermal output is just 1 watt, less than that of a candle flame, and it is known as a "zero-power reactor." About 2 meters high and 4 meters in diameter, the reactor is designed to be highly safe and does not produce spent nuclear fuel.
Six educational reactors were once installed at universities across Japan, but only two remain. The other, at Kyoto University, has temporarily suspended operations and is expected to resume practical training no earlier than the next fiscal year.
"I want students to learn what nuclear energy is and how it can be used safely," said Genichiro Wakabayashi, a professor at the Kindai institute.
More than 250 students took part in practical training there in fiscal 2024. The reactor is also widely used by companies for purposes ranging from cancer treatment research to experiments simulating nuclear decommissioning work.
Excluding inspections and other maintenance, it operates for about 130 days a year.
"(It's so busy) there are hardly any days off," Wakabayashi said.
But keeping the reactor running poses a series of challenges.
Kindai University says maintenance and security cost about 200 million yen a year. Revenue from corporate usage fees and government subsidies for practical training amounts to only around 6 million yen annually, with the university covering the deficit from other income.
The reactor also faces a major change in its fuel supply.
The United States, from which the highly enriched uranium fuel was purchased, sought its return because of concerns it could be diverted for use in nuclear weapons. Japanese and U.S. authorities agreed in 2022 that the fuel would be returned.
The reactor must now be converted to use low-enriched uranium fuel, with the university expected to shoulder part of costs estimated at tens of billions of yen.
The financial pressures come as Japan's government has shifted in recent years from reducing dependence on nuclear power in the wake of the Fukushima Daiichi nuclear disaster toward greater use of the technology.
At the same time, however, fewer students are choosing to study nuclear-related subjects.
Education ministry figures show 177 students entered nuclear-related university departments and programs in fiscal 2024, down to about 30 percent of the 579 recorded in fiscal 1994.
Wakabayashi warned that losing educational reactors could further undermine Japan's ability to train the next generation of nuclear specialists.
"If educational reactors disappear, young people could end up going overseas," he said, calling for greater government support to keep them operating.
Shunji Matsuoka, a Waseda University professor specializing in environmental economics and policy, said hands-on experience with educational reactors was important for developing personnel not only to operate commercial reactors but also to work in decommissioning.
Universities, he said, need to "show transparency in how the reactors are operated, broaden understanding of their value to society and train nuclear specialists who are open and engaged with society."
