Crud Behaviors in High-Temperature Water, (III)Chemical Form of Cobalt-60 in JMTR OWL-1 Loop Water

Abstract

Solvent extraction of Co with diethyldithiocarbamate (DDC) has been applied to the determination of the chemical state of Co in OWL-1 loop water installed in JMTR. The 7593% of the "soluble" ⁶⁰Co are in a form to be easily extracted, Co(II)²⁺, and 522% are in a form being transformed to an extractable form at pH 5.5. The rest, a few percent, is in non-extractable state, possibly in a fine particle. These results are consistent with the general concept that majority of ⁶⁰Co in "soluble" fraction is in a state of Co (II)²⁺ in the primary coolant of nuclear reactor. It is also noticed that in contact with air in alkaline media a slow oxidation of Co (II) (OH)₂ to Co (III) (OH)₃ tends to occur at an apparent oxidation rate of
-d[ Co (II)]/dt=k[ Co (II)][O₂]^1/4.
This oxidation leads to the decrease of the extractability.