A Model for Cobalt 60/58 Deposition on Primary Coolant Piping in a Boiling Water Reactor

Opportunity exists in current BWRs to minimize or reduce the radiation fields which are present in the reactor coolant circuitry when the reactor is shut down. The major contributors to this radiation are two isotopes of cobalt, Cobalt 60 and Cobalt 58. Cobalt 58 is important in the early shutdown period, but the real isotope of concern is Cobalt 60, which is long-lived and has a substantial gamma activity. In order to control the radiation buildup, which currently averages about 100 mR per effective full power year, it is important to understand how the cobalt is deposited on the pipe surfaces. It is just as important to understand how the cobalt gets activated to Cobalt 60 and the nickel to Cobalt 58, and how the cobalt gets activated to Cobalt 60 and the nickel to Cobalt 58, and how these species are released from their activation sites and transported to the out-of-reactor pipe surface. However, this paper will address only the deposition of the isotope and a separate effort is underway which will attempt to bring quantitative understanding to the activation, release and transport mechanisms.