Above: An emergency diesel genset from China’s CSSC
instructions, guidance, and part replacement frequencies relevant to the 1A EDG and the associated lube oil and fuel oil systems, in part, would have ensured appropriate preventive maintenance actions.” The failure to perform these maintenance tasks consistent with station and vendor guidance caused or contributed to an imbalanced fuel condition in the engine, ultimately resulting in its failure. Root cause analysis by the company and NRC identified
two root causes: ● Site leadership did not consistently engage workers
to reinforce foreign material exclusion programme requirements and behaviours necessary to achieve sustained event-free performance prior to the August 2020 1A emergency diesel generator system outage window.
● Excellence in maintenance foreign material exclusion programme behaviours were not implemented and applied during the August 2020, 1A emergency diesel generator system outage window.
A contributing cause was that the site did not effectively use performance improvement tools to drive foreign material exclusion programme improvements prior to the 1A emergency diesel generator system outage window in August 2020. Finally in April 2024 the NRC concluded that:
● Engineering personnel did not successfully identify fuel injector preventive and predictive maintenance strategies for the Société Alsacienne De Constructions Mecaniques De Mulhouse (SACM) diesel generators, which includes the 1A emergency diesel generator.
● System engineers and engineering managers did not exercise adequate technical human performance behaviours and technical conscience principles when developing the preventive maintenance strategy for the SACM diesel generators.
Catawba At the Catawba plant, in a communication on 24 April 2025, NRC identified the root cause of a failure to implement measures to maintain functionality of the ventilation system in one of the diesel buildings. It said the licensee failed to recognise that the alternate method to operate the system was not described in the Updated Final Safety Analysis Report (UFSAR) and inadequate actions were taken to ensure UFSAR-defined testing was incorporated into surveillance test procedures.
Davis-Besse At the Davis-Besse plant, in January 2022 the NRC confirmed a root-cause analysis regarding the unavailability and
inoperability of its Division 2 EDG. The issue was failing to select a speed switch which was suitable for operation within the safety-related EDGs when it was being relied upon for plant safety. Rather than an issue with the EDG itself, NRC cited less than adequate incorporation, internalisation and anchoring of operating and in-house experiences around the unique design vulnerabilities in the direct current (DC) distribution system.
Joseph M Farley At the Joseph M Farley plant, the NRC put to rest a performance issue in a 24 January 2024 letter. The issue involved a failure to provide adequate qualitative or quantitative acceptance criteria in work instructions during maintenance activities on the ‘B’ EDG. Inadequate qualitative or quantitative acceptance criteria in the work instructions on reassembly of the valve cap for a lubricating oil check valve led to the valve cap being damaged on 11 October 2023, which ultimately resulted in a 2.3 gallons per minute lubricating oil leak. Plant staff evaluation identified two root causes.
The first was that the emergency EDG circulating lube oil pump discharge piping restraint was inadequate to prevent coupling separation. The second was that the circulating lube oil system failure mode was not identified and corrected in November 2022 because of “deficiencies and implementation weaknesses” in the troubleshooting process. Maintenance leadership did not enforce compliance with the company’s ‘Management Model’ processes during the planning of the work order to repair a leak on the ‘EDG lube oil gallery supply check valve. As a result, the risk and potential consequences associated with installation of a gasket was not recognised, and work order instructions did not contain sufficient detail to install the gasket successfully. Additionally, the work order was set to ‘Ready’ status before the engineering work was completed. Engineering leadership did not reinforce the use of technical rigour or enforce compliance with the Management Model processes. As a result, the addition of a gasket was not identified as a configuration change, the risk and potential consequences associated with the repair strategy were not recognized, applicable design considerations and impacts were not evaluated, and no torque value was specified.
North Anna 2
At North Anna 2 the NRC confirmed in a communication dated 24 January 2025 that the root cause of a failure to have documented instructions appropriate to the circumstances for foreign material control was inadequate
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