Plenty of radioactive ruthenium-103, ruthenium-106, and stable ruthenium are formed by the fission process. The ruthenium in PUREX raffinate can become oxidized to form volatile ruthenium tetroxide which forms a purple vapour above the surface of the aqueous liquor. The ruthenium tetroxide is very similar to osmium tetroxide; the ruthenium compound is a stronger oxidant which enables it to form deposits by reacting with other substances. In this way the ruthenium in a reprocessing plant is very mobile, difficult to stabilize, and can be found in odd places. It has been called extremely troublesome and has a notorious reputation as an especially difficult product to handle during reprocessing. Voloxidation combined with cold trap collection of the flue gases could recover the volatile ruthenium tetroxide before it can become a nuisance in further processing. After the radioactive isotopes have had time to decay, recovered ruthenium could be sold at its relatively high market value.
In addition, the ruthenium in PUREX raffinate forms a large number of nitrosyl complexes which makes the chemistry of the ruthenium very complex. The ligand exchange rate at ruthenium and rhodium tends to be long, hence it can take a long time for a ruthenium or rhodium compound to react.
At Chernobyl, during the fire, the ruthenium became volatile and behaved differently from many of the other metallic fission products. Some of the particles which were emitted by the fire were very rich in ruthenium.
As the longest-lived radioactive isotope ruthenium-106 has a half-life of only 373.59 days, it has been suggested that the ruthenium and palladium in PUREX raffinate should be used as a source of the metals after allowing the radioactive isotopes to decay. After ten half life cycles have passed over 99.96% of any radioisotope is stable. For Ru-106 this is 3,735.9 days or about 10 years.