What is creep, and in which reactor components is it a design consideration?

• A. Time-dependent deformation under sustained high temperature; important for hot sections and supports near the core.
• B. Rapid brittle fracture under low temperatures.
• C. Magnetic grain alignment at low irradiation doses.
• D. Chemical corrosion due to coolant pH.

Answer: (A)

Creep is time-dependent deformation under sustained high temperature. When a material carries a steady load in the hot regions of a reactor, atoms can diffuse and dislocations move slowly, causing the part to deform gradually even if the load isn’t large enough to cause immediate yielding. In a nuclear plant, many components near the core stay very hot and bear stresses from pressure, weight, and thermal gradients. These “hot sections” and their supports are prime design considerations for creep, because over years of operation the material can sag, lose precise clearances, or drift out of alignment if it creeps too much. Designers address this by selecting creep-resistant materials, deriving creep-life and safety margins from high-temperature data, and setting operating limits to keep deformation within acceptable bounds. The other options describe phenomena that aren’t about slow, time-dependent deformation at high temperature—brittle fracture at low temperature, magnetic grain effects at low irradiation, and chemical corrosion from coolant chemistry.