Pressure stresses are induced in vessels containing pressurized materials. What is a prime example?

• A. Cooling pipes
• B. Fuel rods
• C. Containment shell
• D. Reactor vessel

Answer: (D)

When a vessel holds a fluid at high pressure, the fluid pushes outward on the walls, creating tensile stresses in the vessel material that must be resisted. The reactor vessel is the prime example because it routinely contains reactor coolant at high pressure to prevent boiling. That internal pressure drives significant hoop (circumferential) and longitudinal stresses in the vessel walls, which the vessel must be designed to withstand with adequate margin. The containment shell also experiences pressure, but its role is to contain pressure during abnormal events, not to house the primary pressurized medium in normal operation. Cooling pipes and fuel rods don’t contain pressurized material in the same way—the coolant flows through the system, and fuel rods themselves are solid fuel assemblies surrounded by coolant, not large pressurized vessels. So the reactor vessel most directly illustrates pressure stresses from a pressurized medium.