The Nuclear Regulatory Commission (NRC) has released its interim special inspection report on the Feb. 3, 2021, event at the NIST Center for Neutron Research. The report confirms that the public was safe at all times and that all safety systems and staff performed as expected. Radiation released during the event remained well below regulatory health and safety limits at all times.
The research reactor will remain shut down while NIST conducts a thorough investigation into the root cause of the event. The reactor will not be restarted until that investigation is completed and the NRC authorizes a restart.
According to the report, the NRC confirmed NIST’s calculations and verified that any dose to “members of the public for this event is less than 0.5 millirem (a standard chest X-ray is approximately 10 millirem).”
On March 2, 2021, NIST reported to the NRC that a single fuel element exceeded a temperature safety limit of 450 C (842 F). The NRC’s interim report indicates this was indeed the case, noting that inspectors observed in the video surveillance “a small amount of material that was potentially once molten deposited on the lower grid plate surfaces near the displaced fuel element nozzle. While actual conditions inside the fuel element during the event are still under investigation, the inspectors note that the aluminum alloy used for fuel cladding would melt if temperatures reached a range of 1076 F – 1202 F (580 C – 650 C).”
The facility is designed to keep the public safe in the event of a fuel failure even more significant than the one that occurred on Feb. 3. The NRC reports that “as a result of the event, members of the public and occupational workers remained safe” and that there was no detectable impact on the environment.
As noted in the report, “additional information is needed to draw definite conclusions about the condition of the fuel element and deposited material.” NIST continues its inspection of the interior of the reactor and is in the process of planning the safe removal and study of the damaged fuel element to determine the most likely cause of that damage.
Once the root cause analysis has been completed, NIST will develop a plan for corrective and preventive actions that will be reviewed by the NRC. Additionally, NIST plans to engage external, independent experts to assess the event, its cause and planned actions.
The NIST Center for Neutron Research is an important national resource, providing a premier research facility to approximately 3,000 researchers from across the U.S. each year. It accounts for more than 50% of the neutron research conducted in the U.S. and over the past 50 years has improved our understanding of a wide variety of materials and phenomena.
NIST leadership and staff are committed to determining what caused the Feb. 3, 2021, event and to ensuring the safety of our staff, visitors and community.