Safety Aspects of Using Gadolinium as Burnable Poison in Pressurized Water Reactors

Within the framework of an experimental program on the behavior of gadolinium in light water reactors (LWRs), the BR3 power plant, a small 11-MW(electric) pressurized water reactor, was operated successfully with a core containing 5% Gd₂O₃-UO₂ rods. The core reached an average burnup increase of 22 000 MWd/tM, corresponding to 500 effective full-power days in a single cycle. These results lead us to extrapolate the consequences on safety of extending such a control policy to large LWRs. In this context, the following factors were investigated: impact on the design, reactivity control and core behavior operated with lower and more constant boric acid concentration, environmental impact, fuel handling, etc. The results of this analysis suggest that studies on more elaborate models should be pursued and that the field of investigation should be broadened.