Conference Proceedings Paper
FUEL BEHAVIOUR AFTER A LOCA FOLLOWED BY A SITE DESIGN EARTHQUAKE AT 24 HOURS AFTER THE INITIAL EVENT
13th International Conference on CANDU Fuel - 2016 Aug. 15-18
E.R. Istrate (Cernavoda NPP)
Following a LOCA event, the long term decay power removal is ensured by low pressure ECC pumped flow. As per design, a Site Design Earthquake (SDE) can occur at 24 h after the initial assumed event. Following such a sequence of events, electrical power supply may be lost to the ECC pump(s) and no more forced circulation will be actually available for broken loop fuel cooling. Restoration of the alternate electrical power supply is estimated to occur no later than 30 minutes. However, during this time interval, the broken loop will continue to loose water inventory and fuel will be facing reversed flow or even stagnant conditions. Depending on the duration of these conditions, locally the coolant from the fuel channel may evaporate, generating steam while the fuel sheath and adjacent pressure tube will start to heat-up. Supplementary fuel failures may occur if the duration of the stagnant conditions is significant and fuel sheath temperature increases significantly. When the steam reaches one of the end fittings, the metal will start to heat-up and will condense the steam. Finally, the end fitting will heat-up significantly and the steam will be vented to the associated reactor header, allowing the water to re-enter the affected fuel channel. The paper will present the main results related to broken loop fuel behaviour at 24 h ours after a LOCA event when a SDE event is assumed to occur.
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