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2 Publications

Analysis of PWR core behaviour after the entrance of underborated water

Kliem, S.; Rohde, U.; Weiß, F.-P.

For a realistic description of the coolant mixing during stationary and transient processes inside the reactor pressure vessel, a fast running semi-analytical model has been developed. This model is based on the technique of linear superposition of response functions on Dirac impulse shaped perturbation functions. The model has been coupled to the 3D neutron kinetic core model DYN3D.

A parameter study for a hypothetical boron dilution event including stationary and transient core calculations has been carried out. For the analysis a generic core loading pattern of the PWR KONVOI has been used. By varying the initial slug volume was found, that slugs of less than 16 m3 do not lead to over-criticality in stationary calculations. Transient calculations with higher slug volumes revealed a further conservatism of the calculations. An initial slug volume of 20 m3 is necessary to reach over-criticality in transient calculations. This leads to a significant reactivity insertion into the core and results in a power peak of more than 6500 MW. The power excursion is stopped by the Doppler feedback very effectively. The limited integral energy release does not lead to a significant rise of the coolant temperature. In the calculation with the bounding slug volume, the magnitude of the power peak is with about 8500 MW higher than in the previous calculation. The Doppler feedback stops the further power increase, too. Contrary to the 20 m3 case, the power peak occurs even before the boron concentration has reached its minimum. Because the positive reactivity insertion is continued after the power peak, typical secondary power peaks are observed. At the location of the power maximum, coolant boiling with a maximum void fraction of up to 70 % occurs for a short time. However, no heat transfer crisis was obtained.

The influence of the cross section library on the results of the boron dilution transient has been investigated by using an alternative library. Differences in global core parameters lead to quantitative differences in the time and the height of the power excursion.

A special model, based on a particle-in-cell method for the description of the boron transport through the reactor core has been used. It is shown, that a proper description of the boron transport in case of transients with low fluid velocity is absolutely necessary to calculate the neutron kinetic behaviour of the core in a right manner.

According to all calculations, even a reactivity insertion of about 2 $ connected with a 36 m3 slug did not lead to safety relevant consequences. The power excursion is mitigated and stopped by the Doppler feedback.

  • Lecture (Conference)
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.85-96
  • Contribution to proceedings
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.85-96

Permalink: https://www.hzdr.de/publications/Publ-5421
Publ.-Id: 5421