The Cobalt Reduction Sourcebook includes a tabulated list of available cobalt reduction methods, with expected costs and estimated time required to observe radiation field reduction benefits.

The most significant contributor to both boiling water reactor (BWR) and pressurized water reactor (PWR) out-of-core radiation fields is elemental cobalt and nickel activating to radioactive Co-60 and Co-58, respectively.

Strategies for preventing or removing cobalt from primary circuit materials are detailed in the Cobalt Reduction Sourcebook (1021103), which supersedes a 1993 guidelines document on cobalt reduction (TR-103296).

The Sourcebook summarizes BWR and PWR system-specific cobalt contributors; reviews plant design, operations, and maintenance actions that may result in higher radiation fields; and describes various mitigation methods. A two-pronged cobalt reduction strategy is provided: 1) A tabulated list of available cobalt reduction methods, with expected costs and estimated time required to observe radiation field reduction benefits (see example below); and 2) A series of flowcharts for implementing a cobalt reduction strategy for BWR and PWR plants.

Much of the information in the 1993 document, such as the guidance on valve replacement, is still valid, but the many intervening advances in cobalt reduction techniques warranted the Sourcebook revision. For example, the Sourcebook recommends evaluation of operational strategies such as zinc injection and decontamination when considering cobalt reduction. The Sourcebook also recognizes that low-pressure turbine blades are significant cobalt contributors in BWRs, and these elemental contributions have been quantified. A technical basis using utility data from the SRMP (Standard Radiation Monitoring Program) and BRAC (BWR Radiation Assessment and Control) programs is provided for most of the technologies described.

For more information, contact Dan Wells at 650.855.8630 or dwells@epri.com.

PWR Cobalt Reduction Options
(partial list; full table evaluates 14 technologies/strategies)

Technology/ Strategy	Benefits	Concerns	Expected Time Before Dose Rate Reduction
Improved valve maintenance monitoring with X-ray fluorescence	Reduce Stellite particles to core	None	2-3 cycles for core fuel replacement needed before expected reduction in reactor water 60Co concentrations. Best case 60Co decay curve after core replacement.
Local system chemical decontamination	High decontamination factors on piping	Waste and critical path	Immediate reduction of dose rates
In-vessel vacuuming	Removes particulate activity	Filters must be handled and stored	Immediate reduction of local particulate radiation fields