What materials are commonly used for spent fuel pool racks and what aging concerns exist?

• A. Stainless steels (304/316) or aluminum alloys; aging concerns include corrosion, irradiation damage, and hydrogen cracking.
• B. Carbon steel with epoxy coatings; aging concerns include galvanic corrosion.
• C. Titanium alloys; aging concerns include hydrogen embrittlement only.
• D. Copper alloys; aging concerns include thermal expansion.

Answer: (A)

Racks in spent fuel pools are chosen for their ability to resist water-based corrosion and to hold up under neutron irradiation while staying compatible with pool chemistry. Stainless steels such as 304/316 and aluminum alloys are commonly used because they combine strong corrosion resistance in the borated pool environment with good mechanical properties and manageable activation after irradiation.

Aging in service is driven by three main concerns. First, corrosion from the circulating water can lead to general or localized degradation and, in some cases, stress corrosion cracking depending on water chemistry. Second, irradiation damage from neutrons can alter the metal’s microstructure, causing hardening, embrittlement, and other property changes that reduce the rack’s toughness and durability. Third, hydrogen-related cracking is a risk because radiolysis of water produces hydrogen that can diffuse through metal under stress, promoting cracking in susceptible materials.

These materials balance resistance to corrosion, stability under irradiation, and a manageable aging profile, which is why they’re favored. Other options like carbon steel with coatings, titanium, or copper alloys face greater issues with coating degradation, hydrogen embrittlement, or unfavorable neutron interactions, making them less suitable for long-term pool service.