Maryland Research Reactor to Restart After Safety Pause

The Nuclear Regulatory Commission (NRC) recently granted the National Institute of Standards and Technology (NIST) the go-ahead to restart its research reactor in Gaithersburg, Maryland, after an unsecured latch caused a fuel element to overheat in February 2021.

 

A shot of the NIST Center for Neutron Research in Maryland. Image used courtesy of the National Institute of Standards and Technology

 

In the two years since then, NIST’s Center for Neutron Research (NCNR) corrected its fuel handling and management activities, emergency response procedures, and other actions that led the NRC to conclude the facility met its requirements to ensure critical systems and components run safely. 

The reactor is home to research using thermal and cold neutrons. Its instruments pass intense beams of cold neutrons through an advanced liquid hydrogen moderator. This gives researchers an unmatched glimpse into molecules, materials, and structures. Built in the 1960s and operational in 1969, the facility accounts for half of all neutron research in the U.S., ranging from material science and vaccines to fuel cells for EVs to high-density data storage systems. Producing 20 megawatts (MW) of thermal power, the reactor operates at a lower temperature and pressure than electricity-generating nuclear plants, which typically produce 1 gigawatt (GW).

 

A 2017 photo of the cold neutron guide hall at the NCNR featuring the disk chopper spectrometer and other instruments. Image used courtesy of the National Institute of Standards and Technology 

 

The NRC recently released its 36-page technical evaluation report detailing what occurred on Feb. 3, 2021, from the reactor starting up and approaching full power to the subsequent shutdown due to indications of high exhaust stack radiation. 

The facility’s gaseous effluent monitors detected a rise in radiation, triggering the reactor’s safety system to automatically insert all four shim rods in a “major scram.” This activated the confinement isolation system, which closed all penetrations, including the ventilation valve, process piping, guide tubes, and staff access. However, one of the 30 fuel elements in the reactor’s core was damaged, resulting in molten fuel material spreading to the nearby lower grid plate by exiting through the coolant system nozzle area. Small pieces of the material also left the top of the upper portion of the element and entered the reactor’s primary coolant system. 

Fortunately, the safety and health of NCNR’s staff and the broader public remain unaffected by the incident, as the maximum radiation release was well below the NRC’s limits. In a Q&A on its website, NIST notes that no other similar events have happened in the reactor’s 54-year history.

 

More About the Safety Incident

According to the NCNR, replacing four of the reactor core’s 30 fuel elements is standard practice after each 38-day run cycle. However, upon restarting the reactor after refueling in early-February 2021, a radiation monitor exceeded its set point and prompted an automatic shutdown. In its event notification report (dated Feb. 3, 2021) to the NRC, NIST disclosed that its stack radiation monitor clocked 100,000 counts per minute amid the release of fission products. Moments earlier, while operating at 50% power (10 MW), the reactor automatically scrammed, and the stack monitor climbed to 50,000 counts per minute. Emergency ventilation mode then kicked in to limit environmental discharge, and employees were decontaminated via showers and changing clothes.

NIST filed another report a month later, revealing that based on video surveillance and radiation readings, NCNR had violated the safety limit requiring the reactor’s fuel cladding temperatures to fall below 842 degrees Fahrenheit. Operations paused while NIST investigated the event and returned to the NRC with its results and proposed corrective actions. 

Seven root causes were identified in the investigation. Some include inadequate management oversight of refueling staffing, a complacent culture, inadequate training/qualification programs, a lack of procedures outlining steps to ensure elements are latched, unenforced procedural compliance, and inadequacies in latch determination equipment and tools. 

The technical report also lays out NIST’s corrective measures and the basis of the NRC’s authorization to resume operations, evaluating the reactor’s structures, systems, and components to ensure no functional damage would bar safe operations. It also said that public health and safety were protected both during and after the event, taking air samples at the site boundary and finding near background radiation levels and below-detectable levels of direct radiation. 

With those conditions met, the reactor is slated to return to full operations shortly, though NIST hasn’t specified a date. In the meantime, NIST’s reactor safety evaluation committee must confirm that all restart conditions have been satisfied before low-power testing begins, which is estimated to take several weeks.

 

NCNR Research Participants and Subject Areas

In a February 2021 meeting at the Gaithersburg campus, NIST Acting Director James Olthoff stated that the reactor ran about 240 days per year and supported 3,000 researchers from 50 American companies, 180 universities, and 30 government agencies. 

But that number has since dwindled after the two-year shutdown. In its annual report last year, NCNR reported fewer research participants than in previous years, including 16 NIST divisions, 22 government laboratories, 32 corporations, and 128 universities. Most of the 723 total research proposals in 2022 focused on the facility’s spectrometers (with 297 proposals), closely followed by small-angle neutron scattering (274) and reflectometers (100). 

 

This graph from NCNR’s 2022 annual report (page 59) charts the facility’s research participant categories since 1986. Image used courtesy of NIST Center for Neutron Research

 

Some of the research at the NCNR ranges from advancing fuel cell technology to identifying vaccine structures to devising methods to sense electric fields through walls. It also works with carmakers on neutron imaging projects. NCNR’s last annual report mentions an ongoing partnership between NIST, General Motors, and Honda, using neutron imaging to visualize hydrogen materials for higher-performing fuel cells for EVs.