Which barrier contains radionuclides that escaped cladding or were produced outside cladding?

• A. Containment
• B. RCS pressure boundary
• C. Fuel pellet and cladding
• D. Shielding

Answer: (B)

Radionuclide containment is viewed as a series of barriers. If some radionuclides escape the fuel cladding or are produced outside it, they remain inside the reactor’s primary coolant loop. The boundary that contains them at that point is the Reactor Coolant System (RCS) pressure boundary, which encloses the primary loop and keeps the coolant—and any leaked or generated radionuclides—confined. Only if the primary boundary is breached would radionuclides potentially reach containment, the next barrier. Shielding, while important for dose reduction, does not act as a containment barrier for released material.