The computer code for the accurate prediction of the pressure in the pressurizer under both transient and accident conditions were developed using the three region model.
The mathematical model derived from the general conservation equations includes most of thermal hydraulic processes occurring in the pressurizer: bulk flashing and condensation, wall condensation, interfacial heat and mass transfer etc. The Stanton number for the interfacial heat transfer coefficient was obtained by fitting the experimental results in terms of the surge rate. The bubble rising and rain-out models were developed to describe bulk flashing and condensation, respectively. In order to obtain the wall condensation rate, a one dimensional heat conduction equation was solved by the pivotting method.
The mathematical model was numerically solved by the back substitution and successive iteration method for fast convergence and any stability limitation.
In order to verify the present work, several numerical tests were done on the mild transient in the SHIPPINGPORT NUCLEAR POWER PLANT, the experiment tests done at M.I.T., and the TMI accident. It was proved that results predicted by the present work were in better agreement with experimental tests than those done by the previous model.
Sensitivity analysis was done to see the effect of each model on the behavior of the pressurizer. Discrepancy between results predicted with the three region model and with the two region model became apparent in an outsurge after insurge transient and the former model predicted more accurately than the latter. Although the interfacial heat transfer of the pressurizer can be neglected in the case of the high water level, it becomes one of the most dominant processes in the low level. The wall condensation rate becomes important with an increase in pressure due to an insurge transient.