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Severe oscillations in loop mass flowrate, observed during the two-phase natural circulation in LOBI Test A2-77A, have been analysed using the RELAP5 code and available experimental data. These oscillations manifest themselves in the form of intermittent flow surges followed by repeating intervals of flow stagnation. They arise from the periodic formation and collapse of water levels in the loop seal pipework and SG U-tubes, via a process which is associated with the flow of steam through various bypass junctions interconnecting the hot and cold legs. This paper addresses the phenomenological aspects of the proposed destabilising mechanism and considers possible implications for other plant.

Additional information

Authors: WORTH B, JRC Ispra (IT)
Bibliographic Reference: Paper presented: Eurotherm Seminar No. 16, Pisa (IT), Oct. 10-12, 1990
Availability: Available from (1) as Paper EN 35589 ORA
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