Which materials are commonly used for control rods in PWRs?

Which materials are commonly used for control rods in PWRs?

• A. Graphite
• B. Uranium
• C. Stainless steel
• D. Boron carbide, silver-indium-cadmium, and hafnium

Answer: (D)

Control rods regulate the reactor by soaking up neutrons, so they’re made from materials with high neutron absorption that stay stable under reactor conditions. Boron carbide is a strong absorber because it contains boron-10, offering a high absorption cross-section for thermal neutrons and good stability at high temperatures. Silver-indium-cadmium alloy is effective across a broad neutron energy range and can be formed into compact, durable rods, providing quick and reliable reactivity control. Hafnium also has an exceptionally high thermal neutron absorption cross-section and behaves well under irradiation, making it a powerful absorber option in control rods. Using this combination gives robust, controllable neutron absorption suited to PWR environments. Graphite acts as a moderator, not an absorber. Uranium is fuel, not a absorber. Stainless steel is structural/cladding material and does not provide the needed neutron absorption for effective control.

Control rods regulate the reactor by soaking up neutrons, so they’re made from materials with high neutron absorption that stay stable under reactor conditions. Boron carbide is a strong absorber because it contains boron-10, offering a high absorption cross-section for thermal neutrons and good stability at high temperatures. Silver-indium-cadmium alloy is effective across a broad neutron energy range and can be formed into compact, durable rods, providing quick and reliable reactivity control. Hafnium also has an exceptionally high thermal neutron absorption cross-section and behaves well under irradiation, making it a powerful absorber option in control rods. Using this combination gives robust, controllable neutron absorption suited to PWR environments.

Graphite acts as a moderator, not an absorber. Uranium is fuel, not a absorber. Stainless steel is structural/cladding material and does not provide the needed neutron absorption for effective control.