[en] The dynamic response of a Mark I pressure-suppression system during the early air discharging phase of a postulated loss-of-coolant accident (LOCA) was studied via scale model experiments. Tests using a 11.7-scale model yielded quantitative information on the vent-clearing process, the pool swell, the loads on the torus and the ringheader, and many other dynamic responses of interest. Corresponding information for the reference plant from which the model is scaled can be obtained from the test results and the scaling laws which are given in the report