Jules Horowitz Reactor
The Jules Horowitz Reactor (RJH) is a 100 MW, water-cooled and water-moderated materials testing reactor being built at Cadarache in southern France. It follows the European Roadmap for Research Infrastructures (ESFRI) guidance from 2006 and is named after the French nuclear scientist Jules Horowitz. RJH is designed to have a favorable neutron economy, providing a large supply of thermal neutrons around the outside of the core. These neutrons can be used for testing materials, fuels, and other experiments, and the core allows samples to be inserted directly for exposure to high-energy neutrons, which is helpful for isotope preparation.
Historically, many similar reactors were built in the 1950s and 1960s, but most are now aging or retired. This has created challenges for producing medical isotopes, one of the main roles RJH is intended to support. Construction of RJH began with site preparation in 2007, the first concrete in 2009, and the central containment structure completed with a 105-tonne dome in 2013. The project was initially expected to be ready in 2014, but it has faced major delays and a reorganization of management. Current plans place first criticality well after 2030, with estimates around 2032–2034.
RJH will operate at about 100 MW and features a modular design that can support up to 20 simultaneous experiments. It is intended to be adaptable for research by nuclear utilities, fuel manufacturers, research organizations, and safety authorities, and will enable real-time analysis through advanced instrumentation. Its main uses include studying how nuclear fuel performs at existing reactors, testing materials for reactor use, evaluating designs for future fuels, and producing radioisotopes for medicine. The reactor’s isotope production will be coordinated with facilities at Petten in the Netherlands.
Technical and logistical details include an ascending coolant flow of about 2.36 m3/s and maximum pressure around 1.0–1.5 MPa, depending on flow and core head loss. RJH is part of a broader international effort and is funded by a consortium including France’s CEA, the Czech Republic’s NRI, Spain’s CIEMAT, Finland’s VTT, Belgium’s SCK•CEN, the UK’s NNL, the European Commission, and private companies EDF, Vattenfall, and Areva, with two non-European associates, India’s DAE and Japan’s JAEA. The project is also associated with the IAEA’s ICERR program, making RJH available to IAEA member states for education and joint research.
The program has faced substantial cost overruns and schedule slippage, contributing to the cancellation of other projects and a formal government audit in 2019. A new organizational structure was put in place in 2020, with the outlook for completion extended further into the 2030s as of the latest updates.
This page was last edited on 2 February 2026, at 14:07 (CET).