NIST gets confirmatory order 18 months after research reactor fuel failure

August 3, 2022, 7:01AMNuclear News
NIST's Center for Neutron Research in suburban Gaithersburg, Md. (Photo: NIST)

The Nuclear Regulatory Commission announced on August 2 that it had issued a confirmatory order to the National Institute of Standards and Technology (NIST) for violating NRC requirements during a February 2021 fuel failure at the 20-MWt NIST Center for Neutron Research (NCNR) research reactor in Gaithersburg, Md. NIST committed to improving its training for fuel handing procedures and related management activities, safety culture program, reactor facility operations staff and management, corrective action program and operational procedures, and emergency response resources and procedures, among other things.

“Based on the NCNR’s completed and planned actions, as well as its commitments described in the Confirmatory Order, the NRC has not imposed a civil penalty or issued a cited notice of violation and will not pursue any further enforcement action,” NIST stated in its own August 2 press release.

Incident recap: On February 3, 2021, the NCNR reactor was being restarted after a refueling outage. As the reactor approached full power, several radiation monitors, including the confinement exhaust stack radiation monitor, showed a sudden increase, indicating a release of fission products and a probable fuel cladding failure. The reactor automatically scrammed, and staff declared an alert. Investigations showed that one fuel element had not been properly latched in place and was not in normal grid position in the reactor core. This prevented adequate coolant flow to the fuel element, and a fuel cladding failure occurred in a matter of minutes. No reactor structures, apart from the single fuel element, were damaged, and the reactor has remained in a stable shutdown condition since the incident.

NRC findings: In March 2022, the NRC released the findings of a special inspection that identified seven apparent violations, including five related to exceeding the fuel cladding temperature safety limit and damaging a fuel element. Other violations were related to emergency planning and equipment modification. While public health and safety were maintained during and after the event and doses to reactor facility staff were well below regulatory limits, the “most significant” violation, according to the confirmatory order, involved a safety limit that was violated when the temperature of the fuel cladding of a single fuel element in the reactor exceeded 842°F, allowing the fuel element to partially melt.

NIST’s own root cause analysis of the incident was submitted to the NRC in October 2021. NIST opted for a mediated settlement through the agency’s alternative dispute resolution process, and the confirmatory order enforces the results of that settlement.

According to the confirmatory order, the NRC and NCNR agreed that the safety significance of the violations would normally be characterized at Severity Level 1 in accordance with the NRC Enforcement Policy. “Additionally, the NRC concluded that a civil penalty of up to $432,000 would normally be proposed for this violation, as assessed in accordance with the civil penalty assessment process discussed in Section 2.3.4 of the NRC Enforcement Policy. However, due to the robust nature of corrective actions taken and planned by NCNR . . . the NRC determined that waiving a civil penalty is appropriate in this case.”

More on corrective actions: NIST reports it has already completed many corrective actions, including improvements to the NCNR safety culture; changes to how reactor operations are managed and staff members are trained; and updated procedures, including a new requirement for fuel element latch verification through both mechanical and visual methods, which was recently approved by the NRC.

“All of us at NIST are committed to undertaking the comprehensive corrective actions that will ensure a strong safety culture at the NCNR and prevent something like this from happening again,” said Laurie E. Locascio, NIST director and undersecretary of commerce for standards and technology. “We appreciate the NRC’s engagement with NIST, and we have already made many changes and improvements so that this important national resource can return to safe operation.”

NIST has also agreed to contract with a third-party nuclear consultant to conduct an assessment of the NCNR’s safety culture and help the NCNR implement any recommendations and corrective actions identified in the assessment. Additional information on the February incident, including all previous updates from NIST, can be found on the NIST website.

Restart plans: Since the event resulted in a violation of the fuel cladding temperature safety limit, the NRC must formally approve a restart of the reactor, which NIST requested in October 2021.

According to the NRC, a restart will not be considered until “the agency has completed reviewing the restart request and has determined that sufficient corrective actions have been implemented to ensure that the facility will be operated safely by the licensee.” Once a restart is authorized, the NRC would exercise increased oversight of the facility.

The NRC has scheduled a public meeting later this month to discuss restart-related activities, including the agency’s plans to inspect NIST’s corrective actions.

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