
U.S. Nuclear Regulatory Commission

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Anticipated Transient Without Scram (ATWS)

ATWS is one of the "worst case" accidents, consideration of which frequently motivates the NRC to take regulatory action. The accident could happen if the system that provides a highly reliable means of shutting down the reactor (scram system) fails to work during a reactor event (anticipated transient). They types of events considered are those used for designing the plant.