ABSTRACT
The reliability problem of decay heat removal system falls into the category of a tolerable downtime reliability problem in which failure of safety barriers are hazardous if the duration of failure exceeds its tolerable grace period determined by
1 INTRODUCTION
Sodium cooled Fast Reactors (SFRs) present the characteristic of the large thermal inertia of its coolant systems and high coolant temperature (Saez 2013, Lee & McCormick 2011). This characteristic promotes usage of passive cooling systems and also allows for relatively long times for cooling recovery (Nayak & Sinha 2007) during reactor accidents. Particularly, the large thermal inertia allows a sufficient grace period or tolerance time for the possibility to recover failed components in a DHR system. This possibility of repair within a tolerable downtime or grace period has been further boosted by recent developments in the area of sensor-based online maintenance. For instance, the tools of online integrated risk monitoring system can detect the problem rapidly and possible repair can be realized within the time window given by the thermal inertia of DHR systems (Hashemian 2011, IAEA: TECDOC 1999). Robotic repair system in highly automated plants can restore the fault that was not possible by human interventions (Thomas 2012). Efforts are going on in the area of maintenance to repair a component without hampering the normal operation of a complex engineering system.
