What materials are typically used for reactor pressure vessel (RPV) internals?

• A. Low alloy steels (SA-508/SA-533) and stainless steel components in select areas
• B. High-strength stainless steel only
• C. Pure copper
• D. Aluminum alloys

Answer: (A)

RPV internals are chosen to endure neutron irradiation, high temperature, and the reactor coolant environment, so the materials must balance strength, toughness, weldability, and corrosion resistance. The typical choice is low alloy steel forging such as SA-508 and SA-533 for the majority of the internal structures, providing reliable mechanical performance under irradiation and after many years of service. In selected areas where corrosion resistance or irradiation behavior is especially important, stainless steel components are added to improve performance where needed. Materials like pure copper or aluminum alloys aren’t used for internals because they don’t deliver the required mechanical integrity and irradiation performance in the reactor water, and relying on only high-strength stainless steel would not provide the overall balance needed for all internal parts. So the standard approach is a combination: low alloy steels for the main internals, with stainless steel in chosen areas.