An Investigation of Oxide Layer Impact on Heat Transfer in MARIA Reactor Fuel Element

Within the framework of test fuel examination it has been performed the irradiation of one of fuel elements to high level of burnup (ca. 60 %). Post-irradiation examinations proved that under high burnup it comes to local detachment of oxide layer from the fuel element cladding. Unilateral breaking away of the oxide layer of strong insulation properties from cladding surface may lead to disturbance of conditions for heat removal from the fuel. This effect has been numerically modeled by means of ANSYS FLUENT code. The numerical results confirmed the existence of heat flux redistribution in the spot of oxide layer detachment. Since the phenomenon for breaking away of oxide layer appears at high fuel burnup the thermal loads are getting lower than in most thermally loaded fuel elements so the safety margins for fuel operation are being preserved.