Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

In the integral test facility "INKA" at AREVA NP GmbH in Karlstein, Germany, different passive safety systems of the boiling water reactor concept "KERENA" are being tested. One of these systems is the emergency condenser (EC) which starts automatically in case of a loss of coolant accident with the descent of the filling level in the reactor pressure vessel causing fast heat dissipation. For the exact balance and description of the processes in the emergency condenser a more precise understanding of the two-phase flow in the EC pipes is essential. In this paper we describe the instrumentation of the EC bundle itself as well as the condensate line with thermo needle probes to determine the phase distribution and phase temperatures with high temporal resolution of 10 kHz along the EC circuit. The needle probes have been designed for fast local measurement of void fraction and temperature under extreme conditions like water-steam ambience under 310°C and 9 MPa. The phase measurement is realized by use of an electrical conductivity signal measured at the probe tip. A micro-sheath thermocouple serves as the measuring electrode, hence the conductivity and the temperature signal can be measured simultaneously exactly at the same position in the flow. With this technology it is possible to differentiate between steam and non-condensable gases. Additionally, the EC return pipe has been instrumented with a multichannel gamma densitometer to measure the cross-sectional gas fraction in the condensate line. The gamma densitometer measures the ray attenuation of gamma rays from a Cs137 source along 34 single beams through the 200 mm steel pipe at 10 Hz sampling rate. From these attenuation data the cross-sectional void fraction can be calculated with an accuracy of about 3 %. The paper gives a short overview of the passive safety concept of the KERENA system, the development of the special instrumentation and measuring techniques for extreme temperatures and pressure and discusses the first experimental results in the INKA test facility in Karlstein.