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ROCOM experiments on the influence of density differences on the coolant mixing inside the reactor pressure vessel of a PWR

Kliem, S.; Prasser, H.-M.; Grunwald, G.; Rohde, U.; Höhne, T.; Weiß, F.-P.

During emergency core cooling (ECC) injection into the cold leg of a PWR an incomplete mixing of the injected water with the natural circulation flow in the loop takes place. Due to the higher density of the ECC water a streak of cold water is flowing downwards the downcomer. This causes thermal loads on the reactor pressure vessel wall. Furthermore, the core behaviour is determined by the resulting parameter distributions at the core inlet.
An experimental study was carried out at the ROCOM test facility, a fluid dynamic model of a German type PWR (KONVOI 1300 MWe) in the scale of 1:5. Natural circulation conditions in one loop were approximated by running the corresponding pump at low rotation speed by means of a frequency transformer system. The higher density of the injected water was simulated by adding sugar. The evolution of the spatial distribution of the ECC water was measured by tracering with sodium chloride. Conductivity distributions reflecting the share of ECC water present at given time and location were measured by electrode mesh sensors, one close to the reactor inlet nozzle (16 x 16 measuring points), two sensors in the upper and lower part of the downcomer (2D grids of 4 radial and 64 angular measuring positions) and one sensor at the core entrance (inlets of each of 193 fuel elements).
The paper presents visualisations of the streak effect in the downcomer. The transition from momentum driven flow in the downcomer to a density driven regime was identified (critical Froude number). In the experiments the relative density difference was varied between 0 and 10 % and the loop flow rate between 0 and 15 % of the nominal. The streak effect is more pronounced at higher density differences.

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2002, Stuttgart, Germany, May 14-16, 2002 Proceedings pp. 65-69
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2002, Stuttgart, Germany, May 14-16, 2002 Proceedings pp. 65-69

Permalink: https://www.hzdr.de/publications/Publ-4225
Publ.-Id: 4225