SPECIAL REPORT | EMERGENCY DIESEL GENSETS
Finding lessons in the familiar
Emergency diesel generators need care and attention, as much as the rest of a nuclear unit. That should be a reminder for ‘next generation’ nuclear.
DIESEL GENERATORS HAVE BEEN WORKHORSES since Rudolf Diesel invented the engine that bears his name in the closing years of the nineteenth century. But familiarity cannot mean inattention, especially for those diesel generators that provide emergency back-up power to nuclear stations. While they might be among the most easily-recognised pieces of equipment on site to visitors from outside the industry, their task is uniquely testing for both equipment and the personnel who maintain them, as they have to be ready to start up immediately, even if they are never used in an emergency over the many decades of the plant lifetime. Emergency diesel generator (EDG) issues have been cited
several times in performance issue notices published by the US Nuclear Regulatory Commission (NRC) since the start of the century, most of which detail resolution of an issue that allowed plants to be returned to a ‘green’ state from a slightly elevated ‘white’ state. The performance issues were all resolved to NRC’s satisfaction, but they illustrate how important it is that a positive safety culture is pervasive within a nuclear environment and that it extends to the conventional balance of plant.
Plant by plant At Calvert Cliffs, a communication dated 24 April 2023 deals with an event when an EDG experienced an engine cylinder failure and tripped during routine testing, due to foreign material in the engine. Constellation performed and documented a root cause
evaluation and found the foreign material was most likely introduced during maintenance on the 1A EDG on 22 August 2020, and remained there until the failure. It said that larger pieces of foreign material had been present in the system, which had to degrade to a size that would allow introduction into the fuel injector before the performance issue would be detectable. It said there were no opportunities to identify the foreign material present because no maintenance occurred on the 1A EDG diesel fuel oil system after August 2020 that would have allowed identification of any foreign material present. In October 2023 the NRC discussed failure by Calvert
Cliffs to adequately establish and implement maintenance instructions and practices that reasonably ensured the reliability, availability and operability of the 1A EDG since the engine was originally commissioned. It said: “Adequate
Above: An emergency genset experienced an engine cylinder failure and tripped during routine testing at Calvert Cliffs due to foreign material in the engine Source: Constellation Energy
24 | July 2025 |
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