Considering the application of the pressure suppression containment concept to nuclear ships, there are many problems.
One of them is that when the accident happened, higher pressure buildup in the containment and greater temperature increase of water in the suppression chamber than those of the nuclear power stations would appear because of the compactness of the containment for marine usage. Accordingly, it is worth while to understand the of condensation mechanism of the vented steam at the exit of the vent tube, the necessary submergence depth of the vent tube and the effects of motions and attitude of the ship. The authors investigated experimentally these problems under the conditions that the saturated steam (air content 0-50%, pressure 1.5-18 kg/cm²) was vented through the oriffice (diameter 2-50 mm) into the water (pressure 1-11 kg/cm², subcool 5-100°C), using microflash-photography and high speed films. The summary is as follows.
There are two patterns of vent; the periodic vent which generates large noise and vibration, and the continuous one which is almost silent.
The transition of the periodic vent to the continuous one appears when the ratio of the suppression water pressure to the steam pressure is nearly critical.
The collapses of steam bubbles at the periodic vent are very rapid, and the equivalent condensation heat transfer coefficients at the surface of collapsing steam bubbles are the order of 10⁵-10⁶ kcal/m²h°C and this value decreases when the air content in the steam increases.
A formula for estimating the necessary submergence depth of vent tube is obtained from the data.
The particular feasures are shown when the steam is vented upward and downward. And all of these would be useful to the design works if the sufficient mixing of the water is effected.
Another problem is brought about according to the small capacity of the container, that is, impact of impingement forces produced by the two-phase jet discharging from rupture at pipe or nozzle sections of the primary system would give missile hazards to machineries and instrument apparatus neighbouring to the rupture points inside of the container.
Therefore, to obtain basic informations about the force is very important for the containment system design.
A test facility was installed and a series of vessel blow-down experiments was carried out.
The experimental parameters are rupture pressures 50-90 kg/cm²G, rupture diameters 0.5 inches - 1.5 inches, and the container conditions i. e., dry or wet.
This paper reports obtained data on the intensity variation of the impact force by distance from rupture point, its transient behaviour after rupture, also blowdown phenomena such as pressure-time transient in the system, as well as analysed results.
These results will favour the application of this concept to the nuclear ships.

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