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.
원자로 운전중 발생될 수 있는 과도현상에서 가압기의 압력을 보다 정확하게 예견할 수 있는 전산코드를 three region 모델을 도입하여 개발하였다.
이 가압기 모델은 가열기나 분사장치, 밸브 뿐만 아니라, 가압기내에서 발생될수 있는 대부분의 열수력학적 현상들 - bulk flashing 과 bulk condensation, 가압기 벽에서의 열전달, 물과 증기의 경계면에서의 물질과 열전달등 - 을 포함한다.
이러한 열수력학적 현상들을 포함하여 구성된 수학적 모델은 안정도에 제한없이 빠른시간내에 수렴할 수 있도록 역대입 및 반복법을 이용하여 풀려졌다.
이 모델의 정확도를 조사하기 위하여 shippingport 원자력 발전소 및 M.I.T. 의 실험과 TMI 사고에 대한 Simulation이 수행되었다. 또한, Three region 모델과 Two region 모델의 비교 와 가압기 벽의 효과 및 경계면 열전달 효과에 대한 민감도 분석이 더불어 수행되었다.
