Investigations for the transient behaviour of the accumulator's discharge flow in pressurized water reactors in consideration of dynamic heat and mass transfer processes Final report / Untersuchungen zum transienten Ausstroemverhalten der Druckspeicher von Druckwasserreaktoren mit Beruecksichtigung dynamischer Waerme- und Stoffuebergangsprozesse Schlussbericht
- Authors
- Publication Date
- Jan 01, 2001
- Source
- OpenGrey Repository
- Keywords
- Language
- German
- License
- Unknown
Abstract
Within the scope of German reactor safety research the thermal-hydraulic behaviour in accumulators was investigated experimentally and analytically for transient injection. The paper includes the description of two test facilities used for separate effect experiments for the discharge flow of accumulators. Results derived from experiments at a glass facility show the dependency of the nitrogen release processes in the water on the depressurization rate during negative pressure transients and a delay of release. This release delay caused oversaturated solutions and this effect has to be taken into account for the modelling of accumulators. It was not observed coalescence of nitrogen bubbles during rising but the appearance of humid nitrogen above the liquid level. At the test facility TRACEI separate effect experiments were carried out for the investigation of the heat and mass transfer to the nitrogen cushion, the release of nitrogen out of saturated pressurized water and the multidimensional distribution of the gas temperature. The measured data in the nitrogen cushion show different conditions of humid nitrogen such as unsaturated and saturated humid nitrogen, the occurrence of water droplets in terms of fog and frozen fog. Intensive distributions of temperature and humidity above the liquid level were detected during fast pressure gradients, hence high depressurization rates. Post test calculations were accomplished with the ATHLET-Code Mod. 1.2 Cycle B for selected TRACEI separate effect experiments. The comparison of calculated results and experimental data shows well calculated liquid level decreasing and a good agreement of the pressure transient even if the friction pressure loss coefficients of the connection pipe between the accumulator simulator and the venting vessel were adapted. Deviations between simulations and experiments arised in calculating the cushion gas temperature. In order to improve the simulation quality it was suggested to calculate the enthalpy, the density, and accordingly the specific volume and the volumetric gas fraction, respectively the volumetric water fraction, by a model of humid nitrogen bearing analogy to the model of humid air in consideration of the basic equations used in the ATHLET-code. The modelling for releasing of solved nitrogen in the water nodes contains a source term of volumetric gas release rate subjected to pressure and depressurization rate and approaches for the determination of bubble rising velocities of the nitrogen bubbles in water. (orig.) / SIGLE / Available from TIB Hannover: F02B1735 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / Bundesministerium fuer Bildung und Forschung, Berlin (Germany) / DE / Germany