Reactor operators Craig Winder (foreground) and Clint Weigel prepare to start up the ATRC Facility reactor at Idaho National Laboratory after a nearly two-year project to digitally upgrade many of the reactor’s key instrumentation and control systems. Photos: DOE/INL

At first glance, the Advanced Test Reactor Critical (ATRC) Facility has very little in common with a full-size 800- or 1,000-MW nuclear power reactor. The similarities are there, however, as are the lessons to be learned from efforts to modernize the instrumentation and control systems that make them valuable assets, far beyond what their designers had envisioned.

One of four research and test reactors at Idaho National Laboratory, the ATRC is a low-power critical facility that directly supports the operations of INL’s 250-MW Advanced Test Reactor (ATR). Located in the same building, the ATR and the ATRC share the canal used for storing fuel and experiment assemblies between operating cycles.

The Ghana Research Reactor-1, located in Accra, Ghana, was converted from HEU fuel to LEU in 2017. Photo: Argonne National Laboratory

In late 2018, Nigeria’s sole operating nuclear research reactor, NIRR-1, switched to a safer uranium fuel. Coming just 18 months on the heels of a celebrated conversion in Ghana, the NIRR-1 reboot passed without much fanfare. However, the switch marked an important global milestone: NIRR-1 was the last of Africa’s 11 operating research reactors to run on high-enriched uranium fuel.

The 40-year effort to make research reactors safer and more secure by replacing HEU fuel with low-enriched uranium is marked by a succession of quiet but immeasurably significant milestones like these. Before Africa, a team of engineers from many organizations, including the U.S. Department of Energy’s Argonne National Laboratory, concluded its conversion work in South America and Australia. Worldwide, 71 reactors in nearly 40 countries have undergone conversions to LEU, defined as less than 20 percent uranium-235. Another 31 research reactors have been permanently shut down.

International Atomic Energy Agency member states operating or having previously operated a research reactor are responsible for the safe and sustainable management of associated radioactive waste, including research reactor spent nuclear fuel (RRSNF). Management includes storage and ultimate disposal of RRSNF, or the corresponding equivalent waste generated and returned following reprocessing of the spent fuel. Currently, there are 259 research reactors operating, planned, or under construction around the world [1]. An additional 147 research reactors are in extended or permanent shutdown, or under decommissioning.

One key challenge to developing general recommendations for RRSNF management options lies in the diversity of spent fuel types, locations, and national or regional circumstances, rather than mass or volume alone, particularly since typical RRSNF inventories are relatively small. Currently, many countries lack an effective long-term strategy for managing RRSNF. Many research reactor organizations know they have responsibility for the spent fuel, however, they do not know how to decide among multiple options for its management. A methodical review and compilation of technology options for RRSNF management is needed.