Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Nuclear Engineering


Wm. J. Garland


J.-S. Chang


In a pressurizer water nuclear power plant, the pressure of the primary heat transport system is maintained mainly through the operation of a pressurizer. Existing pressurizer models are not satisfactory in predicting pressurizer behaviour in response to operating or accidental transients. This is mainly due to lack of understanding on non-thermodynamic equilibrium and other local two-phase phenomenon in the pressurizer. The primary objectives of this work are to prepare necessary tools for a systematic study of the pressurizer and to investigate pressurizer phenomena under quasi-steady-states and to determine the effects of major pressurizer control parameters to the behaviour of the pressurizer.

To achieve the first objective a rate form of equation of state is analytically derived. It is used as an analytical expression of pressurizer pressure response as well as to support and to guide the rest of the work. lDRIFF, a two-phase simulation code consisting of a lumped homogeneous model and a differentially formulated drift-flux model, is developed to accommodate any physical assumptions in pressurizer modelling. A laboratory scale pressurizer system, complete with a glass pressurizer tank, a simulated primary heat transport system and substantial monitoring facilities is also developed. Together, they provide analytical, numerical and empirical tools needed in a systematic study of pressurizer phenomena.

To achieve the second objective, various quasi-steady-state conditions in the pressurizer are simulated experimentally and four distinct flow regimes are identified in the pressurizer. With the help of numerical extrapolation by using the IDRIFF code, the data are analyzed to produce, among other things, a correlation of average void fraction, a pressurizer flow-regime map with the transitions of flow-patterns semi-analytically modelled, and a general understanding of pressurizer behaviour under quasi-steady-states.

In addition, the effects of changes in pressurizer heater, steam-bleed flow and pressurizer surge-line flow to the behaviour of the pressurizer are investigated. Perturbation transients, where the dynamic effect of the parameters can be isolated from other transient factors, are empirically and numerically simulated. The resulting overall pressurizer behaviour and observed local phenomena are analyzed in terms of their relation to quasi-steady-state behaviour, global and local pressure response, local phase distribution and pressurizer stability. Several flow and heat transfer mechanisms, such as the temperature of the steam being controlled by the liquid saturation pressure, are also summarized.

It is believed that the preparation of research tools and the accumulation of information learnt during the course of the current endeavour has formed an essential basis for a further systematic study of nuclear power plant pressurizer and has brought the study one step closer to the goal of achieving a complete understanding of pressurizer phenomena.

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