Review of GKSS 3-vent experimental program and results

Fifteen multivent steam experiments have been completed. Experimental data indicate, that: increasing mass flow rate into the system causes nearly the same system pressure level but different time periods for condensation oscillation (C.O.) and chugging stage, especially a long chugging period under low steam mass rates; increasing pool start temperature reduces pressure amplitudes especially during chugging in a hot pool with 600C start temperature; decreasing pool back pressure causes a lower system pressure level and increasing pressure amplitudes, especially during CO and chugging by 1 bar; complete global replication of test behaviour was only found in experiments with the same pool back pressure of 1 bar and also in experiments with a higher system pressure but only for special time regimes; chugging nature indicates two pulses, a first pulse induced by a steam collapse outside the vent pipe exit with an oscillation of the vent acoustic frequency and a second subsequent pulse caused by a steam torus collapse inside the vent pipe exit, which excites an attenuating frequency obviously controlled by the natural frequency of the wet well pool-structure-system, sometimes the proceeding pulse with vent pipe acoustic frequency is missed; time interval for synchronous chugging at the 3 vent pipe exits is in the range of 50 to 100 ms. (orig./HP)