PREDICTION OF VVER-TYPE FUEL-ROD BEHAVIOR AT HIGH BURNUP

Fuel rod in-reactor behaviour is subject to a great number of physical and chemical processes that take place during irradiation of the nucl ear fuel elements. The practical difficulties with long-term experimen tal investigation of an in-reactor fuel rod was a major drawback in ev aluating the influence of the main fuel rod design and operational par ameters on its performance. The FRAPCON-2 computer code was used to an alyse the influence of the major fuel pod design parameters on such sa fety characteristics as maximum fuel temperature and gas-gap pressure. Predictions of fuel rod behaviour during normal operation of a Russia n VVER-type reactor to high burnup values (70 000 MWd/tU) are presente d and calculations varying the fuel rod design and material parameters are shown to indicate the strong dependence of important safety chara cteristics on these parameters. The calculations show the influence of initial gas-gap pressure, pellet-clad gap width, initial fuel density and the size of the central hole in the fuel pellet on the fuel assem bly performance.