NIST Research Reactor to Restart Following Two-Year Shutdown

This article is republished with minor changes from the Physics Today website.

The Nuclear Regulatory Commission has authorized the restart of the reactor at the National Institute of Standards and Technology’s Center for Neutron Research (NCNR), more than two years after a radiation incident forced the shutdown of what is the nation’s most productive source of experimental neutrons. Located in Gaithersburg, Maryland, NCNR began low-power operation in mid-March and is expected to open for experiments in May or June, depending on how calibrations and tests go, Center Director Robert Dimeo told Physics Today.

NCNR shuttered its reactor in early February 2021 following an incident in which operators failed to properly secure one of its 30 fuel elements during a routine refueling, causing a disruption in coolant flow during start up. The element was damaged and a radiation release resulted in minor exposure to six workers and contamination of the reactor’s primary cooling system. Monitoring of radiation levels outside the building showed that the public received no appreciable dose, NRC confirmed.

Since then, NRC has worked with NCNR officials to establish the root causes of the accident and to verify implementation of the 23 corrective actions that were developed. Among the commission’s findings was that the facility had inadequate operator training, a lack of management oversight during the refueling process, “a culture of complacency,” written procedures that did not capture all the necessary steps to secure fuel elements, and insufficient enforcement of procedures. The tools and equipment used to determine when fuel elements are properly locked into place were also inadequate, according to NRC. NIST’s corrective actions for each cause were verified by the NRC before restart authorization. The commission will also enhance its surveillance of reactor operations for an unspecified period.

“We’ve reached this decision after extensive review of the event, NIST’s corrective actions, and additional work the facility has done to ensure safe operation,” said Andrea Veil, director of the NRC Office of Nuclear Reactor Regulation, in a statement on March 10. “We’re satisfied this research facility’s important systems and components are ready to go, and we’re satisfied the reactor staff are ready to carry out improved procedures for maintaining safety.”

During the hiatus, scientists have had to cope with the loss of a device that accommodated about 40% of the nation’s neutron-scattering experiments. Efrain Rodriguez, a University of Maryland physicist who explores the crystal and magnetic structures of inorganic materials he makes in his laboratory, said he is excited about the restart. During the shutdown, his students had to move many experiments to the High Flux Isotope Reactor at Oak Ridge National Lab in Tennessee. “We were able to get most of what we needed at Oak Ridge,” he told Physics Today. But because he usually accompanied his students to the NCNR, “an educational component was lost” during the closure.

Since graduate students and postdocs have only a limited time to perform their experiments, many have had to travel to European neutron sources, such as France’s Institut Laue-Langevin and Germany’s FRM-II. Rodriguez said he has heard of some researchers who have gone as far as the Australian Centre for Neutron Scattering to obtain access to neutrons.

The reactor will be operational for about a year to clear a backlog of more than 250 experiments selected in the call for proposals that NIST issued just before the shutdown, Dimeo said. Some proposals also were left over from the suspension of NCNR operations during the start of the COVID pandemic.

After NCNR works through the backlog, the facility will close again to install a new cold neutron source that should nearly double the flux of low-energy neutrons. The installation process is expected to last about a year. The new cold source will enable measurements on small biological samples and viruses as well as time-resolved images that show kinetics, Dimeo explained. “Neutron scattering is a flux-starved technique, and any opportunity you have to get more beam on the sample really allows researchers to do better things.”

During the closure, upgrades will also be made to neutron guides, which transport neutrons from the reactor core to the instruments used for experiments. After the upgrade, a new instrument being built in an NSF-funded partnership with the University of Delaware will be commissioned. Known as a neutron spin-echo instrument, it will probe motion in soft materials such as polymers and biomolecules.