Which aging concern is associated with materials used in spent fuel pool racks?

• A. Hydrogen cracking is an aging concern for materials such as stainless steels or aluminum alloys used in racks.
• B. Hydrogen cracking is not a concern for any rack materials.
• C. Aluminum alloys never suffer aging degradation.
• D. Any rack material is immune to hydrogen cracking.

Answer: (D)

Hydrogen cracking, or hydrogen embrittlement, is a real aging concern for metals used in spent fuel pool racks, such as stainless steels and aluminum alloys. In the pool environment, water chemistry, radiation, and corrosion processes can generate dissolved hydrogen or facilitate hydrogen uptake by the metal. Hydrogen atoms can diffuse into the metal lattice, especially at flaws, welds, or high-stress regions, and weaken the material by reducing ductility and promoting crack initiation and growth over time. This means these rack materials can develop cracks as they age under service conditions, rather than being immune to such degradation. Statements that claim no cracking risk or universal immunity do not hold, because hydrogen embrittlement depends on the specific material, its microstructure, and the environmental conditions in the pool.