Insider word for corrosion products of iron, nickel and cobalt that circulate in the reactor coolant, deposit on fuel cladding where neutrons activate them, then redeposit in piping, valves and steam generators. Activated crud, mainly cobalt-58 and cobalt-60, sets dose rates around primary systems. Chemists manage it with coolant pH, zinc injection and controlled crud bursts during shutdown, when oxidising chemistry releases deposits that cleanup systems then remove.
Crud burst is coming off on the peroxide addition, cobalt-58 is climbing, keep both demins in service.
The popular expansion 'Chalk River Unidentified Deposits' is a backronym; insiders just mean the dirt, and they care most about the cobalt in it.
Also heard as
- corrosion products
- activated corrosion products
Related terms
Activation
The process by which neutrons make stable materials radioactive, creating isotopes such as cobalt-60.
Hot spot
A small spot on piping or equipment with a much higher dose rate than its surroundings.
Flea
Slang for a hot particle, a tiny speck of highly radioactive material found on clothing or skin.
Decontamination
Removal of radioactive contamination from people, tools, surfaces or systems to reduce dose and spread.