Analysis of Operator Responses to Mitigate Temperature Rise in Electrical Auxiliary Building

The loss of air conditioning in the electrical auxiliary building at South Texas Project (STP) has been shown in previous work to result in relatively rapid air temperature rise. The heat up is a concern in the Probabilistic Risk Assessment (PRA) because it may be associated with high conditional core damage probability. As a consequence, operator responses to mitigate the building heat up have been developed and proceduralized at STP. The plant’s current loss of electrical auxiliary building HVAC operator procedure was analyzed and improvements have been recommended. This was done using a commercial computational fluid dynamics (CFD) package that modeled the transient air temperature rise of the building and qualitatively assessed the effectiveness of operator actions. A possible methodology for validating the CFD results was developed using coupled energy balance equations for individual rooms. The methodology is a conservative approach to compare the effectiveness operator actions and provide steps for future higher fidelity simulation and validation. While the specific approach is applicable to STP, the overall methods and approaches described should be applicable to other sites that may be subject to excessive room heat up due to loss of air conditioning in critical rooms.