This paper focuses on testing results of the impact of water contamination in diesel fuel on the ability of an emergency diesel generator (EDG) to successfully start and operate during an emergency. This testing program resulted from the discovery of degraded vent pipes on diesel fuel feed tanks that could have allowed rain water to enter and collect at the bottom of the diesel fuel system and potentially prevent satisfactory engine start-up and operation. The nuclear regulator notified the nuclear plant of a potential yellow finding.
The initial analysis effort focused on the use of diesel engine combustion software (Ricardo’s WAVE© 1D engine performance simulation software). Two medium-speed diesel engine models were analyzed with added water content ranging from 10% to 40% water in the diesel fuel. The analyses demonstrated that the engines could start and operate with those percentages of water in the fuel, but that the engine output would experience a power loss or derate proportional to the water content. The regulator was not convinced that the analysis was sufficient.
The validity of the analytical findings above was demonstrated by full-scale tests conducted by MPR Associates on a large diesel engine. To accomplish this, Entergy, the nuclear power plant owner constructed a simulation of the diesel fuel supply system at a facility having the same make and model EDG. Water was introduced into the diesel fuel day tank by two different approaches; slow trickle flow and large slugs of water. These conditions simulated either a steady rainfall while the EDG was operating or a large volume of water collected in the system while the EDG was in standby.
Under both water contamination scenarios, which consisted of more than 50 hours of testing, the diesel engine and generator set responded with negligible loss of frequency or voltage. Further, the engine was confirmed to have undergone no increased wear or degradation as a result of the high levels of water in the combustion chambers. Following a detailed review of the test program and the successful results, the regulator concluded that neither a non-cited violation nor a penalty was warranted.