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Calculations on UMSICHT Water Hammer Benchmark (Experiment 329) using TRACE and RELAP5. W. Barten, A. Jasiulevicius, O. Zerkak, R. Macian-Juan LRS-Seminar, PSI, 6 April 2006 . Structure. Introduction UMSICHT water hammer experiments TRACE and RELAP5 models of UMSICHT PPP experiment 329
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W. Barten, A. Jasiulevicius, O. Zerkak, R. Macian-Juan
LRS-Seminar, PSI, 6 April 2006
When the water flows back to the valve the vapor is compressed, and the pressure rises.
The vapor temperature increases above the liquid temperature and even beyond the (with increasing pressure) also increasing saturation temperature.
This leads to condensation of vapor, however for base case parameters not as fast as observed in measurements.
After reflection of the pressure wave at the valve, the pressure and saturation temperature decrease again.
With the water flowing back to the valve, the vapor condenses again, the fluid hits the valve, and the second pressure and steam temperature peaks are encountered.Temperature, condensation and flashing (1)
With respect to this the pressure peak considerably increases, since the damping effect by the “void cushion” on the pressure amplitude is reduced.
Moreover the experimentally observed spiky shape of the first peak is now well represented.
At ~2s both codes yield a large vapor production as a result of the increased vaporization rate, which however is not observed in the measurements.
At that time, TRACE predicts the saturation temperature to fall below the liquid temperature.
The high void fraction for RELAP5 is due to the combined effects of the evaporation in the calculation volume and the convection of vapor from neighboring volumes.Temperature, condensation and flashing (2)
Since no direct measurements of volume averaged liquid temperatures are available, we compare the code-calculated liquid temperatures with a local measurement from the wire mesh sensor.
As in the measurements, the TRACE and RELAP5-calculated liquid temperatures vary within a few degrees;
they reflect qualitatively the pressure decrease at ~0.2s and the temperature increase with the first pressure peak.
The temperature spike of 10 to 30 degrees before the first pressure peak in RELAP5 might be regarded as a model deficiency.Temperature, condensation and flashing (3)
Improvements of the two-phase flow and the condensation and flashing models are necessary.
To capture effects of pressure wave propagation on the piping structures can only be correctly simulated by FSI techniques not available in modern nuclear system codes.
Continue analysis of UMSICHT PPP water hammer experiment 329 (and later exp. 135) using TRACE and RELAP5.
Use 3-D capability of TRACE to analyze e.g. Cold Water Hammer Test Facility experiments (CWHTF at FZR).
Couple a mechanical code, ANSYS, to TRACE to account for FSI and analyze further UMSICHT and CWHTF experiments.
Apply TRACE-ANSYS to LOCA (and possibly RIA) for accurate prediction of pressure wave propagation and FSI.Conclusions and Possible Outlook:It is not the pressure (wave/front propagation) alone …