Steam generator modeling considerations for analysis of operational transients

Industry efforts in recent years have increasingly emphasized the operator's role in accident mitigation. This is demonstrated by the many programs dedicated to better prepare the operator for emergency response such as symptom-based emergency operating procedures, simulator validation, and safety parameter display systems. To support these programs, the art of accident analyses is evolving toward operational transients using best-estimate methodologies. The analysis codes are also evolving from their licensing role to training tools for both engineers and plant operators. Whereas licensing basis analyses generally focused on the plant response as it affected the fission product barriers, operational transients require special consideration of the plant parameters that affect operator response. Steam generator pressure is one such parameter. It is used as the primary symptom for secondary-side breaks and alerts the operator to pending challenges to secondary-side relief valves. It also affects the primary loop response for certain accidents such as steam generator tube failures. Some considerations are presented for modeling steam generator pressure response for analysis of operational transients based on plant experiences. To investigate nonequilibrium behavior, the affected steam generator pressure data following the tube failure incident at the R.E. Ginna plant was compared to the calculated pressure response using a homogeneous, equilibrium model