engleski

NPP Krsko IB Modelling with GOTHIC and MELCOR Codes

It is important to determine environmental conditions within nuclear power plant buildings in order to properly design and select electrical equipment that has to perform in such conditions. If the plant conditions are consequence of Design Basis Accidents (DBA), the Equipment Qualification (EQ) is necessary to ensure that safety-critical components and systems have met relevant quality standards. In case of Design Extension Conditions (DEC) similar requirements are covered under term equipment survivability. During NEK EQ program we mostly used GOTHIC code to calculate thermal hydraulic condition inputs for equipment qualification. The accident sequences covered under plant DEC program are calculated mostly using MAAP and MELCOR codes. MELCOR code has general nodalization capability and can be used to model thermal hydraulic conditions in rooms directly or indirectly affected by main accident sequence. In order to see capabilities of both codes, when they are applied to the situation which is within their application scope, we modeled NPP Krško (NEK) Intermediate Building (IB) rooms containing steam and feedwater lines with GOTHIC and MELCOR codes. The transient that was initially analyzed is the Main Steam Line Break (MSLB). The similar results were obtained with main reasons for differences being in break mass and energy release representation and in condensation model on heat structures. The developed IB model is then used to predict rooms atmosphere heatup and hydrogen concentration due to containment design leakage after unmitigated SBO sequence. Again, similar results were obtained, this time mostly influenced by different leakage flow model used in GOTHIC and MELCOR code. In the next phase transport of the radioactive material will be added to the containment leakage flow.

thermal hydraulic conditions, equipment qualification, Intermediate Building, MELCOR, GOTHIC, MSLB

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