|Conference:||LJUBLJANA 2012 - Nuclear Energy for New Europe|
|Title:||Two-phase Subcooled Decompression under Temperature Gradient modelled with WAHA code|
|Author(s):||Oriol Costa, Iztok Tiselj|
|Contact :||Oriol Costa|
|Address:||Institut "Jožef Stefan"
|Author's proposal:||Poster presentation|
The subcooled decompression under temperature gradient experiment performed by Takeda and Noda in 1979 has been reproduced using the in-house code WAHA version 3. The sudden blowdown of a pressurized water pipe under temperature gradient generates a traveling pressure wave that changes from decompression to compression, and vice versa, every time it reaches the two-phase region near the orifice break. The pressure wave amplitude and frequency are obtained at different locations of the pipe’s length. The value of the wave period during the first 20 ms of the experiment seems to be correct but the pressure amplitude is over predicted. The main three parameters that contribute to the pressure wave behavior are: the number of volumes used for the calculation, the break orifice and the ambient pressure at the outlet.
Recent studies using RELAP5 code have reproduced the early pressure wave transient of the same experiment reducing the discharge coefficient and the bubble diameter. In the present paper, the long term pipe pressure, i.e. 2 seconds after rupture, is used to estimate the break orifice that originates the pressure wave. The numerical stability of the WAHA code is clearly proven with the results using different Courant numbers. The over predicted pressure amplitude seems to be the consequence of extra friction factors during the experiment that the one-dimensional two-phase flow WAHA code can’t reproduce.