[en] Within the framework of research project 15 NU 09485, 'Calculation and configuration of the passive emergency condenser of an innovative, natural-convection BWR (SWR600) using the ATHLET code', which is closely connected with research project 15 NU 9050, 'Emergency condenser for a medium-output BWR - experiments for performance assessment', measurements were carried out at the NOKO experimental facility for identification of flow regimes and condensation processes. The task was to measure the flow regimes in the NOKO tube by means of needle-type conductuivity probes. The probes were placed into a single heat transfer tube (NOKO single tube) specifically installed for this purpose at the NOKO experimental facility. Several probes were inserted in each of two selected flow sections so that the phase distribution could be measured dynamically during liquid level lowering, i.e. at the probes positioned in downward level direction. The shape of the phase boundaries was reconstructed from the measured data. This arrangement of the probes detects and yields measured data of the various flow regimes occurring. (orig./DG)

No abstract available

[en] Published in summary form only

[en] Air-water two-phase flow tests in a large vertical pipe of 194.1-mm inner diameter (i.d.) are reported. Close to the outlet of a 9-m-tall test section, two wire-mesh sensors are installed that deliver instantaneous void fraction distributions over the entire cross section with a resolution of 3 mm and 2500 Hz used for fast-flow visualization. Void fraction profiles, gas velocity profiles, and bubble-size distributions were obtained. A comparison to a small pipe of 52.3-mm i.d. (DN50) revealed significant scaling effects. Here, the increase of the airflow rate leads to a transition from bubbly via slug to churn-turbulent flow. This is accompanied by an appearance of a second peak in the bubble-size distribution. A similar behavior was found in the large pipe; though the large bubbles have a significantly larger diameter at identical superficial velocities, the peak is less high but wider. These bubbles move more freely in the large pipe and show more deformations. The shapes of such large bubbles were characterized in three dimensions. They can be rather complicated and far from ideal Taylor bubbles. Also, the small bubble fraction tends to bigger sizes in the large pipe

[en] Two-phase flow tests in a 194.1 mm diameter vertical pipe (DN200) with an air-water mixture are reported. Close to the upper end of a 9 m tall test section a wire-mesh sensor is installed that delivers instantaneous void fraction distributions over the entire cross section with time resolution of 2500 frames per second. The sensor disposes of 64 x 64 measuring points, which corresponds to a spatial resolution of 3 mm. Beside an fast flow visualisations, void-fraction profiles and bubble size distributions were obtained. Earlier, similar experiments were carried out in a pipe of 51.2 mm inner diameter (DN50). A comparison of the data from the two different facilities allows to study the scaling effects on void fraction profiles, bubbles size distributions and the flow patterns. In the small pipe, the increase of the air flow rate leads to a transition from bubbly via slug to churn turbulent flow. The transition to slug flow is accompanied by the appearance of a second peak in the bubble size distribution that corresponds to the class of large Taylor bubbles. A similar qualitative behaviour was found in the large pipe, though the large bubble fraction has a significantly bigger mean diameter at identical superficial velocities, the peak is less tall but wider. Bubbles move more freely than in the small pipe, since the confining action of the pipe walls to the flow is less pronounced, while the large Taylor bubbles occupy almost the entire cross section in case of the small pipe. Furthermore, the bubbles show much more deformations in the large pipe. Shapes of such large bubbles were characterised in three dimensions for the first time. They can rather be complicated and far from the shape of ideal Taylor bubbles. Also the small bubble fraction tends to bigger sizes in the large pipe

No abstract available

[en] Some of the accident scenarios discussed for WWER-440 reactors assume an over-feed of the secondary side of the steam generators by water coming either from the primary side or from the feed water system. 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 WWER-440/213, was extended by a steam-line model, which is equipped with a novel two-phase flow instrumentation as well as fast pressure and displacement transducers. The poster has the following structure: Introduction; Description of the test facility; Special instrumentation / mesh sensor; Special instrumentation / local void probes; Test conditions / test results

[en] The report presents experiments which were aimed at studying steam condensation in horizontal respectively slightly inclined pipes at high driving temperature differences of up to 200 K. Further specifics are the detailed investigation of the transient behaviour of a non-condensable gas using a novel measuring technique as well as the evaluation of the influence of the gas upon the condensation intensity. For this purpose in the experiment a rapid transient process was realized, which was initiated by suddenly connecting a heat exchanger pipe resting in a pool of cooling water with the steam dome of a pressure vessel. In the pipe, different initial conditions were adjusted by varying the initial pressure of the non-condensable gas (air). Experiments were carried out with atmospheric pressure, with increased air pressure, but also with an evacuated pipe. The new instrumentation consists in novel needle-shaped void probes, which allow the local phase detection combined with a fast temperature measurement. This makes it possible to study the redistribution of steam, condensate and non-condensable as a function of time with a high resolution. The obtained data offer the possibility to validate the models for the prediction of the transport and the effect of non-condensable gases in thermal hydraulic system codes under transient conditions. (orig.)

[en] The present paper deals with advanced conductivity probes for local void measurements, which were equipped with a microthermocouple, which is integrated into the probe at the place of the electrode wire. These probes were used for rapid transient condensation tests in a heat exchanger pipe immersed into a cooling water tank. The experiments serve as data sources for the validation of thermal-hydraulic system codes concerning the modelling of the condensation, particularly with respect to the behaviour and effect of non-condensable gases. The present tests were carried out at the pressurizer test facility DHVA of the University for Applied Sciences in Zittau/Goerlitz, IPM serving as steam source. The slightly downwards inclined condensation tube was connected to the head of the pressure vessel and supplied with steam in this way. The application of a new type of two-phase instrumentation has revealed details about the transient condensation process. Since tests were performed with and without the presence of a non-condensable gas (air), the effect of the gas could be studied. The merits of the probes lie in the ability to distinguish between steam and gas. Without the synchronous temperature and void measurement performed by the probes it would have not been possible to clarify the physical background of the temperature jumps found during the experiments with the non-condensable gas. (orig.)

[en] The paper presents the results of a thermal hydraulic experiment conducted at the PMK-2 test facility within the IMPAMVVER project. The test was dedicated to a loss-of-coolant event during the cool-down phase of the plant, when neither core flooding tanks nor safety injections systems are automatically available. Though fuel rod dryout occurs, the activation of one of four lines of low pressure emergency injection is sufficient to re-establish reliable core cooling. In the cooling-down situation, the primary circuit is pressurised with nitrogen, therefore, non-condensable gas can enter the primary circuit from the pressurizer during the blow-down phase. The transport of the nitrogen along the primary circuit was studied with a novel type of a local void probe equipped with an integrated micro-thermocouple. RELAP5 was found to be able to predict the behaviour of the non-condensable gas in the primary circuit. Despite of some delay in the prediction of the time of the appearance of the gaseous phase in the begin of the process, most details of the transient were well reproduced by the code. (orig.)