Which material is the primary source of Co-60 in the reactor coolant system?

Which material is the primary source of Co-60 in the reactor coolant system?

• A. Stainless steel
• B. Aluminum
• C. Copper
• D. Stellite

Answer: (D)

Cobalt-60 in a reactor coolant system mainly comes from neutron activation of cobalt-59 that is present in materials exposed to the reactor’s neutron flux. The material contributing most is Stellite, a cobalt-containing alloy used for hard-facing and wear-resistant surfaces on components like valve seats and stems. When irradiated, cobalt-59 captures a neutron and becomes cobalt-60, which then decays and emits gamma radiation, becoming a primary source of activation in the system. Stainless steel does have cobalt only as a trace impurity, and aluminum and copper contain little cobalt, so they contribute far less to Co-60 production. Thus, Stellite is the primary source.

Cobalt-60 in a reactor coolant system mainly comes from neutron activation of cobalt-59 that is present in materials exposed to the reactor’s neutron flux. The material contributing most is Stellite, a cobalt-containing alloy used for hard-facing and wear-resistant surfaces on components like valve seats and stems. When irradiated, cobalt-59 captures a neutron and becomes cobalt-60, which then decays and emits gamma radiation, becoming a primary source of activation in the system. Stainless steel does have cobalt only as a trace impurity, and aluminum and copper contain little cobalt, so they contribute far less to Co-60 production. Thus, Stellite is the primary source.