TABLE OF CONTENTS An initial release of a steam water mixture with a high internal energy into the containment takes place in many water reactor accident scenarios. Typically, it is the water of the primary cooling system which causes an initial overpressure and a subsequent pressure transient in the containment itself. The following paragraphs describe some simple methods, with essential data, for calculating the pressure with time in these two phases.
A note concerning measurement units used in these calculations has to be added. Due to the long history of the first creation of the related computer program and of its subsequent improvements and tests, the measurement units don't all belong to the Standard International (SI) system. They have been left as they were, in order not to lose the benefit, in terms of reliability, of the long testing of the program. The strongest discrepancy from the SI units is that large calories (Cal) are used instead of Joules and bars or kg/cm 2 instead of Pascals.
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 (an intermediate or large LOCA). Therefore, the heat exchanged with objects internal...
