A2-2 Initial overpressure

The initial pressurization of the containment is a constant volume phenomenon (the containment volume) and therefore, in order to calculate the final state parameters (e.g. the pressure), it is necessary to equate the initial and final internal energies of the involved fluids. Here it is assumed that the initial pressurization of the containment is relatively fast, for example corresponding to the break of an intermediate or large recirculation pipe 

The initial and final energies of the fluids concerned can be calculated by the following considerations and formulae. 

Specific internal energy of the water — steam mixture, 

The quality, X, of the mixture, before and after the pressurization of the containment, can be calculated from the specific volumes of the water and steam which are known. The weight of water and steam is equal to the released amount (e.g. that of the primary cooling water), while the initial volume is 

Example The containment has a free volume of 60000 m, into which 250 t of primary water are released, with an average temperature of 300°C. Initially the pressure in the containment is equal to 1 bar. Therefore V fP = 0.24 m  

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