VALIDATION OF AN ELECTROCHEMICAL MODEL FOR THE OXIDATIVE DISSOLUTION OF USED CANDU FUEL

Measured dissolution rates of UO2 and used fuel powders are compared t o dissolution rates predicted from electrochemical measurements on fue l pellets. This comparison was made for rates as a function of dissolv ed oxygen concentration, carbonate/bicarbonate concentration, and gamm a irradiation dose rate. Measurements were also made as a function of temperature over the range 25-75 degrees C. Good agreement was obtaine d between measured and predicted rates in aerated carbonate solutions confirming that the dissolution reaction is electrochemical in mechani sm and that its rate can be predicted electrochemically. For non-compl exing solutions agreement was not as good since electrochemical measur ements on dissolution of fuel pellets appeared to be inhibited by the formation of secondary phases in occluded grain boundaries. Measured d issolution rates on powders do not appear to be affected in this manne r since few occluded grain boundaries are present. Predicted and measu red rates in gamma irradiated solutions, while measured under differen t conditions, showed the same general trends, and compare well to publ ished literature values. In aerated non-complexing solutions and in ae rated carbonate solutions the effect of gamma irradiation becomes insi gnificant below similar to 1 Gy h(-1) and similar to 10 Gy h(-1), resp ectively. Crown copyright (C) 1998 Published by Elsevier Science B.V. All rights reserved.