Improvement of the design of the series-produced fuel element of the VV�R-440 reactor to increase burnup

Abstract

The fuel elements for the VVER-440, which were developed for a 4-yr run, operate satisfactorily to an average burnup of 59 MW-day/kg of uranium in the most-stressed fuel element with average burnup of the unloaded fuel of 40 MW-day/kg. Through the introduction of end beveling of the pellets, the mobility of the fuel column is increased. Furthermore, the presence of bevels makes possible a reduction of the number of chips and elimination of process crumbs, and the high mobility of the fuel column makes it possible, during outfitting of the fuel element, to eliminate the axial gaps between pellets, which are unacceptable for safety reasons. The increase in the initial helium gage pressure has made possible substantial improvement of the thermomechanical characteristics of the fuel elements and avoidance of high fuel temperatures and large gas release. When the conversion is made to a 4-yr fuel run, the number of fuel assemblies refueled each year decreases from 117 to 90 per power-generating unit, natural uranium consumption is reduced by 11–12% [2], zirconium consumption is lowered, and the effective capacity of burned-up fuel stores is increased.