In reactor systems such as Inertial Confinement Fusion , Liquid Metal Fast Breeder Reactors , and High Temperature Gas Cooled Reactors the designs allow for even higher temperatures. Due to the high temperatures involved, creep needs to be accounted for when designing nuclear power systems. In order to understand how creep affects nuclear power systems its mechanisms and hence its behavior must first be understood. Before this can be done a review of basic mechanical behavior principles is warranted. First a few definitions are in order.
Stress is defined as the amount of force per unit area.
Strain on the other hand is defined as the extension of a sample divided by its initial length. Elastic behavior, as the name suggests, is the strain of a material that is not permanent and returns to zero when the applied stress is removed. A good example of elastic behavior is the behavior of a rubber band. On the other hand plastic behavior describes a material whose strain does not return to zero when the stress is removed. A good example of plastic behavior is the plastic behavior of taffy.