Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

2 Publications

Coolant Mixing in Pressurized Water Reactors at Constant Coolant Flow in the Primary Circuit

Grunwald, G.; Höhne, T.; Prasser, H.-M.; Weiß, F.-P.

During transients in Pressurised Water Reactors the quality of the coolant may differ from one loop to another. Both an undesired decrease of the boron acid concentration (boron dilution transient) and a decrease of the coolant temperature in case of a main steam line break lead to a positive reactivity insertion, which may cause a power excursion. In general, both temperature and boron acid concentration at the inlet nozzles of the reactor vessel can vary as independent functions of time. On the way to the core entrance the coolant from different loops is mixed in the threedimensional turbulent flow field inside the complex boundary conditions of downcomer and lower plenum. The consequences to the reactor core depend very sensitively on the degree of mixing. In the present work, a German 1300 MW PWR was investigated. For this purpose, the ROCOM test facility (Rossendorf Coolant Mixing Model) was built. The new facility disposes of four complete loops with controllable pumps in each of them. This allows to study a wide range of different mixing scenarios. The presented results on stationary mixing, i.e. mixing of a permanently disturbed coolant flow in one of the loops with running circulation in all four loops are in good agreement with the results of previous work. The maximum value of the averaged mixing scalar at the core inlet was found to be about 90 %, i.e. 90 % of the coolant arriving at the most affected fuel element origins from the disturbed loop. New information was obtained concerning the transient behaviour of the concentration field. The experiments have shown the mechanism of mixing in case of short plugs. Furthermore, strong fluctuations of the instantaneous mixing scalar were found, especially at the slopes of the averaged distribution. These fluctuations where quantified for the first time. It has to be checked whether these effects must be considered in 3D neutron kinetic models.

Keywords: coolant mixing; pressurized water reactor; boron delution transient; main steam line break; coolant mixing experiments; conductivity sensors

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2000, 23.-25. Mai 2000 in Bonn, Proceedings pp. 109-114.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2000, 23.-25. Mai 2000 in Bonn, Proceedings pp. 109-114.

Publ.-Id: 3106