NUMERICAL SIMULATION OF THE COOLANT FLOW IN PRESSURIZED WATER REACTORS


NUMERICAL SIMULATION OF THE COOLANT FLOW IN PRESSURIZED WATER REACTORS

Höhne, T.

The behavior of PWRs during cold water or boron dilution transients is strongly influenced by the distribution of coolant temperature and boron concentration at the core inlet. This distribution is required as an input to 3-dimensional neutron kinetics to calculate the power distribution in the core. It mainly depends on how the plugs of cold or unborated water formed in a single loop are mixed in the downcomer and in the lower plenum [1]. The reactivity insertion due to penetration of unborated coolant into the core depends on the degree of mixing. Weak mixing can result in recriticality and possibly in significant power release. The same is true for cold water insertion into the core due to overcooling of a coolant loop in the case of a steam line break. Coolant mixing is also of interest under steady state normal operation conditions. Slight differences in the cold leg temperatures can occur due to small asymmetries in the primary circuit loops.

To simulate such mixture phenomena requires the application of 3-dimensional CFD (computational fluid dynamics) codes. The results of the simulation have to be validated against mixing experiments at scaled facilities. The calculations are accomplished using the CFD Code CFX-4.2 [2].

As a first step, steady state mixing conditions in the downcomer and lower plenum are considered. Qualitatively different flow fields were found in different reactor types depending from the downcomer geometry. Calculated results were compared with experiments.

  • Lecture (Conference)
    CFX International Users Conference, Friedrichshafen, Germany 19-24 June 1999, CD-ROM, No. 27
  • Contribution to proceedings
    CFX International Users Conference, Friedrichshafen, Germany 19-24 June 1999, CD-ROM, No. 27

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