In the course of a nine-day release by the Chernobyl reactor in April-
May 1986, ruthenium was considered to have been emitted at the same ra
te as other refractory elements. In fact, there are indications that t
he release was more important than previously estimated and lasted for
tens of days because of oxidation of Ru into volatile forms. This pap
er demonstrates that, when put in contact with air, small uranium oxid
e particles can release 100% of radioruthenium at temperatures of the
order of 1000 degrees C.