Criteria for ATWS

An anticipated transient without scram (ATWS) is defined as an abnormal transient followed by failure of a reactor scram. Since the Super LWR is a simplified LWR, the probability of an ATWS is expected to be on the same order as that of LWRs. An ATWS of the Super LWR is classified as a beyond design basis event (BDBE). A deterministic evaluation of an ATWS is a global requirement because it is a potential safety issue that may lead to core damage under postulated conditions. Also, it is expected that inherent safety characteristics of nuclear reactors, not only reactivity feedback but also reactor system dynamics, can be clearly identified at ATWS conditions due to a scram failure. Therefore, deterministic ATWS analyses are carried out for the Super LWR in Sect. 6.7 as well as the abnormal transients and accidents. 

Despite the significantly low probability of an ATWS compared to other accidents, the same criteria as those of accidents are applied, as in LWRs. It should be noted that release of fission product gases to the coolant does not bring about an 

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