Hydrodynamic phenomena in the downcomer during flow rate transients in the primary circuit of a PWR

Mixing phenomena observed when the flow rate in a single loop of the primary circuit is changed can influence the operation of pressurized water reactor (PWR) by inducing local gradients of boron concentration or coolant temperature. Analysis of one-dimensional Laser Doppler Anemometry (LDA) measurements during the start-up and shutdown of pump on a single loop of the ROCOM test facility has been performed. The effect of a step change and a ramped change in the flow rate on the axial and azimuthal velocities was examined. Numerical simulations were also performed for the step change in the flow rate that gave quantitative agreement with the axial velocities. Phenomenological agreement was made on the turbulent kinetic energy; however, observed values were a factor of 2.5 less than the turbulent kinetic energy derived from the measurements.

[1]  M. Michard,et al.  Analysis of the swirl effect on turbulent length scales in an ICE cylinder by two-point LDV , 2001 .

[2]  H. Prasser,et al.  A new electrode-mesh tomograph for gas–liquid flows , 1998 .

[3]  Florian R. Menter,et al.  CFD Best Practice Guidelines for CFD Code Validation for Reactor- Safety Applications , 2002 .

[4]  G. Katul,et al.  Scalar dispersion within a model canopy: Measurements and three-dimensional Lagrangian models , 2006 .

[5]  D. Wilcox.  Turbulence modeling for CFD , 1993 .

[6]  Frank-Peter Weiss,et al.  Coolant Mixing in a Pressurized Water Reactor: Deboration Transients, Steam-Line Breaks, and Emergency Core Cooling Injection , 2003 .

[7]  W. Kastner,et al.  Thermal hydraulics of PWRS with respect to boron dilution phenomena. Experimental results from the test facilities PKL and UPTF , 2001 .

[8]  S. Orszag,et al.  Renormalization group analysis of turbulence. I. Basic theory , 1986, Physical review letters.

[9]  Soeren Kliem,et al.  Fluid mixing and flow distribution in the reactor circuit, measurement data base , 2005 .

[10]  H. Hodson,et al.  Reynolds stress measurement with a single component laser Doppler anemometer , 2002 .

[11]  Fabien Anselmet,et al.  Simultaneous measurements of temperature and velocity fluctuations in a slightly heated jet combining a cold wire and laser doppler anemometry , 2000 .

[12]  A. Paglianti,et al.  Observations on the significance of instabilities turbulence and intermittent motions on fluid mixing processes in stirred reactors , 2005 .