SPONTANEOUS WATER HAMMERS IN A STEAM LINE IN THE CASE OF COLD WATER INGRESS

Abstract

Some of the accident scenarios discussed for the Russian type pressurized water reactors VVER-440 assume an overfeed of the secondary side of the steam generators by water coming either from the primary side or from the feedwater system. This may happen, for example, in the case of a leakage from the primary to the secondary side, as well as during earthquakes, and can lead to water ingress into the main steam lines, where condensation-induced water hammer may be the consequence. The present work was initiated to study this phenomenon experimentally. For this purpose, the PMK-2 test facility of KFKI-AEKI Budapest, an integral thermohydraulic model of a VVER-440/W213, was extended by a steam-line model, which is equipped with a novel two-phase flow instrumentation as well as fast pressure and strain-gauge transducers. The applied mesh sensor developed by Forschungszentrum Dresden Rossendorf allows a visualization of the transient flow section during the water hammers. Local void probes detect the propagation of slugs along the pipe. The applied new kind of probe is equipped with microthermocouples to provide local instantaneous temperature measurements along with phase detection. This allows assessing temperature gradients at the boundary between the water and steam. The paper describes the test facility and the new instrumentation. The results of the first tests are presented and discussed. The work is part of the WAHALoads project, which was performed within the fifth EU framework program. The objective of the project was to improve the prediction of loads on equipment and support structures of nuclear power plants that are caused by water hammers and shock waves.