Which barrier prevents the escape of fission products from cladding?

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

Answer: (D)

The key idea is that fission products are produced inside the fuel and must be confined by the barriers that surround the fuel. The first line of defense is the fuel itself plus the cladding that surrounds it. The fuel pellet confines most fission products within its solid matrix, and the surrounding cladding provides the next, immediate confinement. Together they form the barrier that prevents fission products from escaping the fuel region.

The other options refer to barriers farther out in the system. Containment is the final outer barrier that prevents release to the environment in an accident scenario, the RCS pressure boundary contains materials within the reactor coolant system, and shielding protects personnel from radiation but does not serve to trap released fission products. Therefore, the barrier most directly preventing escape from the cladding is the combination of the fuel pellet and the cladding.