Meaning of TRANSIENT in English
A change in the reactor coolant system temperature and/or pressure due to a change in power output of the reactor. Transients can be caused (1) by adding or removing neutron poisons, (2) by that is increasing or decreasing electrical load on the turbine generator, or (3) by accident conditions.
NRC Nuclear Energy English Glossary. Английский глоссарий ядерной энергии NRC (Национальный научно исследовательский совет). 2012