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Referring to single phase natural circulation in steam generators with inverted U-tubes, various working conditions can be postulated in response to perturbations in the operating parameters. Clearly, such behaviour is related to potential flow instabilities inherent to parallel channels connected to a common manifold. This paper is aimed at a physical and analytical interpretation of the mechanism governing the onset and eventual divergence of flow surges observed in the LOBI-MOD2 steam generators during the evolution of thermal hydraulic transients relevant to decay heat removal in PWRs. Secondary side heat sink degradation is identified as the primary mechanism leading to the observed instabilities. A generalised analytical steady state model is used to characterise the transient from steam generators' potential operating conditions; a numerical method is then described to account for unstable conditions.

Additional information

Authors: ANNUNZIATO A, JRC Ispra (IT)
Bibliographic Reference: Paper presented: Safety of Thermal Reactors, Portland (US), July 21-25, 1991
Availability: Available from (1) as Paper EN 36237 ORA
Record Number: 199110813 / Last updated on: 1994-12-02
Original language: en
Available languages: en