Event at the National Institute of Standards and Technology (NIST) Center for Neutron Research

Aerial view of the NIST Center for Neutron Research in Gaithersburg, Maryland
Aerial view of the NIST Center for Neutron Research in Gaithersburg, Maryland.  Visit the NIST facility locator page for more information.


On February 3, 2021, the NIST test reactor shut down automatically in response to a higher than normal radiation level in the air leaving the reactor building.  All safety systems functioned properly to shut down the reactor and the reactor remains safely shut down today.  The Nuclear Regulatory Commission (NRC) staff are confident that public health and safety continue to be protected.  Radiation doses inside NIST property were a small fraction of the regulatory limits for members of the public.  Radiation doses beyond the NIST property would have been even lower.  NRC inspection staff are monitoring NIST’s response to the event and NRC approval will be required before NIST can restart the reactor.

Description of the Event and NIST and NRC Responses

On February 3, 2021, NIST restarted its test reactor after a shutdown for refueling and maintenance.  During the startup, shortly after 9 a.m., the safety system automatically shut down the reactor because detectors showed much higher than normal radiation levels in the air leaving the reactor building through the ventilation system.  The reactor operators declared an “Alert” in accordance with the NIST emergency instructions reported it to the NRC shortly before 10 a.m.  An “Alert” designates an event that could be hazardous to personnel in the facility or indicate a problem with the reactor, but shouldn’t have any significant consequences for the public or environment.  After the reactor was shut down, the workers left the building and monitored the reactor using a special station designed for that purpose.  NIST ended the event later that day at 7:35 p.m. Eastern Standard Time because radiation levels were below the criteria in the emergency instructions.

The event had no significant radiological consequences for NIST workers, the public, or the environment.  No one was injured.  Several NIST workers who were inside the building during the event were contaminated with radioactive material and exposed to higher than normal radiation levels.  All workers were decontaminated, and radiation exposures were well below regulatory limits for radiation workers.  Measurements made near the boundary of the NIST campus, about 400 meters from the reactor, showed that radiation levels were near naturally occurring levels.  During the event, potential radiation doses beyond NIST property would have been less than one millirem, a very small fraction of the regulatory annual public dose limit of 100 millirem (the limit is roughly equivalent to several chest X-rays in one year).  The NRC website provides more information about radiation doses in our daily lives.

On February 9, 2021, the NRC began a Special Inspection to examine NIST’s response to the event.  Since then, the NRC inspectors and additional NRC technical experts have been monitoring NIST’s response to the event using onsite inspections at the reactor, virtual attendance of meetings, and remote inspection of documents.  The NRC issued an interim inspection report on April 14, 2021.  The NRC may issue additional interim reports and will issue a final inspection report after concluding the special inspection.

On February 10, 2021, NIST conducted a public meeting to inform the local community about the event.  Several NRC staff attended the meeting to help address public questions and concerns.  Questions and answers from the meeting are available on NIST's website.

As required by the NRC license for the reactor, NIST submitted a report on February 16, 2021, that described the circumstances of the event.  NIST updated the report on March 4, 2021, revising the concentration of airborne radioactive material released during the event slightly upward, but releases were still a small fraction of the regulatory limits.

On March 2, 2021, NIST notified NRC that the temperature of one fuel element exceeded the safety limit during the event and submitted an additional report to the NRC on March 5, 2021.  The report explained that a complete evaluation of the conditions in the reactor and cause of the event will likely take several months.  NIST provided an update to Event Report #55120 on May 7, 2021, and submitted a follow-up written report on May 13, 2021, with a preliminary analysis of the cause of the event.  The report also notified NRC that NIST did not meet several operational requirements in the facility license during the event, in addition to exceeding the fuel temperature safety limit.  NRC regulations require NIST to receive approval from the NRC before restarting the reactor.

NIST submitted a report to the NRC on October 1, 2021, as supplemented on October 15, and 21, 2021, containing the results of its root cause investigations, an analysis of proposed improvements to the fuel element latching mechanism, and a list of recovery items related to the event.  The report also included proposed corrective actions to be completed prior to and following restart of the NIST reactor, and a request to restart, upon completion of the necessary corrective actions.
The NIST root cause investigations revealed one fuel element was not properly latched during the routine refueling outage performed in January 2021.  The improperly latched fuel element became displaced/tilted which blocked the coolant flow into the element and caused the element to overheat while the reactor power level was increased.
The corrective actions that NIST proposed include improvements to the latching procedures and enhancements to operator training.  The list of recovery items includes cleanup of the primary system, evaluation of the fuel elements in the core at the time of the event for reuse, removal of the damaged element, and an operational review of the balance of plant systems.
In response to NIST’s report and request, as supplemented, the NRC staff identified additional information necessary to inform the restart decision.  The NRC sent the information request to NIST in a letter dated November 18, 2021.
The NRC staff will only make a restart decision after fully understanding the event.  The restart decision will be informed by numerous activities including the NRC’s inspection activities and a technical review of NIST corrective actions.  The NRC staff has not committed to a restart schedule and will only authorize restart once the NRC is confident that the facility can be operated safely.  The NRC decision on the NIST request to restart will be based on a finding of reasonable assurance that the facility will be operated in a safe manner and within its existing licensing basis.

Page Last Reviewed/Updated Friday, December 03, 2021