Transient Analysis of the Three Mile Island Unit 2 Pressurizer System

A computer model has been developed to simulate the dynamic behavior of a pressurized water reactor pressurizer system subjected to severe transients. Unique features of this model include

1. a detailed nonlinear model for the surge line that conserves mass, energy, and momentum
2. a three-volume model for the pressurizer volume
3. a kinetic theory model for bulk flashing and condensation
4. representation of spray, heaters, and relief/safety valves.

Two test calculations were performed for verification of the proposed pressurizer system model (PRSZR) including simulation of the Three Mile Island Unit 2 accident, and the planned loss of off-site power at Davis-Besse 1. The results of both tests are in excellent agreement with the plant data. In addition, sensitivity studies were performed that demonstrate that for severe transients the following features of the pressurizer system model are essential—the detailed surge line model, the three-volume pressurizer vessel model, the bulk evaporation/condensation model, and the relief/ safety valve models. It was also found that modeling the electrical heaters and wall condensation were not important, at least for rapid transients.