Over the last 30 years, reactor safety technology has evolved not so much
from a need to recover from accidents or incidents, but primarily from
many groups in the nuclear community asking hypothetical, searching (what
if) questions. This questioning has indeed paid off in establishing
preventive measures for many types of events and potential accidents.
Conditions, such as reactivity excursions, large break, loss of coolant,
core melt, and containment integrity loss, to name a few, were all at one
time topics of protracted discussions on hypothesized events.
Historically, many of these have become multiyear, large-scale research
programs aimed at resolving the "what ifs". For the topic of anticipated
and abnormal plant transients, however, the searching questions and the
research were not so prolific until the mid-1970s. At that time,
probabilistic risk methodologies began to tell us we should change our
emphasis in reactor safety research and development and focus more on
small pipe breaks and plant transients. Three Mile Island punctuated that
message in 1979. The plant transient topic area is a multidisciplinary
subject involving not only the nuclear, fluid flow, and heat transfer
technologies, but also the synergistics of these with the reactor control
systems, the safety systems, operator actions, maintenance and even
management and the economic considerations of a given plant.