The Nuclear Regulatory Commission (NRC) published its preliminary special test report on February 3, 2021 at the NIST Center for Neutron Research. The report confirms that the public has been safe at all times and that all security systems and staff are performing as expected. The radiation released during the event remained well below the legal limit values for health and safety at all times.
The research reactor remains decommissioned while NIST conducts a thorough investigation into the root cause of the event. The reactor will not restart until this investigation is complete and the NRC approves a restart.
According to the report, the NRC confirmed NIST calculations and confirmed that each dose for “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 assembly had exceeded a temperature safety limit of 450 ° C (842 ° F). The NRC interim report indicates that this was indeed the case and that the video surveillance inspectors “observed a small amount of material that may have once melted and deposited on the lower tie plate surfaces near the displaced fuel nozzle. While the actual conditions in the fuel bundle are still being investigated during the event, the inspectors note that the aluminum alloy used for the fuel cladding would melt if temperatures reached a range of 580 to 650 ° C. “
The facility is designed to ensure the safety of the public in the event of a fuel failure even more severe than the one on February 3. The NRC reports that “as a result of the incident, members of the public and workers remained safe” and that there was no demonstrable impact on the environment.
As noted in the report, “additional information is required to draw firm conclusions about the condition of the fuel assembly and deposited material.” NIST is continuing its inspection of the reactor interior and is currently planning the safe removal and investigation of the damaged fuel assembly to determine the most likely cause to determine for this damage.
Upon completion of the root cause analysis, NIST will develop a corrective and preventive action plan that will be reviewed by the NRC. In addition, NIST plans to use external, independent experts to assess the event, its cause and planned actions.
The NIST Center for Neutron Research is an important national resource and provides a world-class research facility for around 3,000 US researchers each year. It accounts for more than 50% of the neutron research done in the US and has improved our understanding of a wide variety of materials and phenomena over the past 50 years.
The management and staff of NIST are eager to determine the causes of the February 3, 2021 event and to ensure the safety of our staff, visitors and the community.
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