IRRADIATION-INDUCED CREEP IN FUEL COMPACTS FOR HIGH-TEMPERATURE REACTOR APPLICATIONS.

Irradiation-induced creep in reactor graphite and in fuel compacts for high-temperature reactors is an important effect leading to a relief of the stresses which build up in fuel elements during reactor operation. In order to obtain information on irradiation-induced creep in these materials at temperatures encountered in a commercial reactor, specimens were subjected to three successive irradiations in the high-flux reactor at Petten. The data were evaluated to obtain the steady-state radiation creep coefficient of the compacts. It was found that, for the materials investigated, the creep coefficient is temperature dependent, but no clear relationship with Young's modulus could be established. Under certain conditions this irradiation-induced plasticity influences the elastic properties, with a concomitant increase of the creep coefficient. This effect coincides with the formation and further opening up of cracks due to stresses caused by irradiation-induced shrinkage of the matrix material.