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Multiphase Science and Technology
SJR: 0.124 SNIP: 0.222 CiteScore™: 0.26

ISSN Print: 0276-1459
ISSN Online: 1943-6181

Multiphase Science and Technology

DOI: 10.1615/MultScienTechn.v23.i1.10
pages 1-27


W. Barten
Paul Scherrer Institut; and 2Swiss Federal Nuclear Safety Inspectorate ENSI, Deterministic Safety Analyses DESA, Brugg Switzerland
Audrius Jasiulevicius
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; and Vattenfall Nuclear Fuel AB, 16287 Stockholm, Sweden
O. Zerkak
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
R. Macian-Juan
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; and Department of Nuclear Engineering, TU Munchen, Boltzmannstrasse 15, D-85748 Garching, Germany


In this paper, we assess the capabilities of the TRACE and RELAP5 codes to model coupled two-phase flow and pressure wave propagations in a piping system, since these codes are two of the most widely used tools to model complex system transients of nuclear facilities. With that aim, using the thermal-hydraulic capabilities of both codes in a spatially 1D approximation, the first few seconds after valve closure in the UMSICHT PPP water hammer experiment 329 have been analyzed considering the time-dependent interconnected behavior of pressure, void fraction, and flow rate at different positions in the pipe. With standard code parameters, the overall flow behavior in the first few seconds and the timing of the pressure excursions, as well as the first generation of void downstream of the valve, are well represented by both codes. The measured collapse of void at the first pressure excursion is underpredicted by both codes, and the predicted pressure excursion is thereby dispersed and damped. While the timing of the second pressure excursion is well predicted by both codes, the experimental damping, presumably being at least partly due to fluid-structure interaction (FSI), is not sufficiently reflected in the modeling results. With scoping calculations using TRACE and applying considerably increased condensation heat transfer rate, the calculated collapse of void with increasing pressure due to the reflection of flow at the valve is much more efficient. The timing, shape, and amplitude of the predicted first pressure excursion is in near-perfect agreement with the measured results, including the spiky shape, while the effects of local void generation and distribution still need improvements. The damping of the second pressure peak, being influenced by FSI with vibrations of the pipe structure, is still underestimated. On the whole, this study demonstrates that the best-estimate system codes TRACE and RELAP5 are potentially useful tools for the analysis of a cavitation water hammer in a pipe, and shows how far the models can calculate measured behavior. In order to use these codes for more accurate prediction of cavitation water hammer behavior, further development work is needed in order to better represent the dynamics of direct-contact condensation and flashing in the considered parameter range and, when needed, FSI.