Slovenia’s TRIGA reactor marks 60 years of research and training

A 250-kW reactor built for hands-on nuclear work is still doing that job 60 years later, and Slovenia is treating the milestone as a live piece of national infrastructure, not a museum piece. On May 25, 2026, the Jožef Stefan Institute marked the TRIGA reactor’s 60th anniversary, and President Nataša Pirc Musar was set to award the institute the Golden Order of Merit for its contribution to science, research and education in nuclear technology.

The Reactor Infrastructure Centre describes the TRIGA Mark II as Slovenia’s central nuclear research infrastructure, with access to the reactor, a hot cells facility and associated equipment for scientific, educational and industrial use. That setup matters because it keeps the work practical: neutron and gamma irradiation, sample handling, training for students and professionals, and the kind of experiments that give reactor physics its real-world edge. The reactor core holds about 70 fuel elements, while a 40-position rotary specimen rack and pneumatic rabbit systems keep irradiation campaigns moving.

The technical record shows why the reactor has stayed relevant. It achieved first criticality on May 31, 1966 at 14:15, was reconstructed in 1991 and equipped for pulse-mode operation, and has continued operating since 1966. Historical and technical sources say it has supported sample irradiation, neutron radiography, reactor-physics experiments, boron neutron capture therapy, environmental studies, advanced materials research and isotope production. IAEA-linked material also notes heavy radioisotope production in the 1970s and 1980s, especially 99mTc and 18F.

The anniversary carries extra weight because the reactor has been tied to Slovenia’s nuclear workforce and safety culture from the start. The institute says the TRIGA contributed to the development of nuclear technology in Slovenia and supported the startup of the Krško nuclear power plant. In February 2026, Foreign Minister Tanja Fajon visited the reactor centre, underscoring Slovenia’s emphasis on responsible nuclear science, international cooperation and science and economic diplomacy.

The site’s hot cells underline that this is still an active working facility, not just a display. The Hot Cells Facility has two hot cells, including VC1, which is connected to the reactor through pneumatic transfer for irradiated samples and fitted with master-slave manipulators. The reactor, hot cells and digester are under continuous radiological spatial monitoring, a reminder that long-lived research infrastructure still runs on discipline as much as hardware.

Leon Cizelj said the reactor’s 60 years have coincided with the institute’s expansion into a multidisciplinary research organization. That is the real story here: the machine that first went critical on May 31, 1966 is still training people, moving samples, producing isotopes and keeping Slovenia’s reactor community connected to the basics that matter.