The surveillance results of the Belgian units were presented and it was shown that they can be adequately represented by the FIS formula, except for Doel 1-2 welds whose chemical composition falls out of the range of applicability of the FIS formula and for which the U.S. Regulatory Guide 1.99 rev. 2 is used instead. The new prediction formula recently proposed in the U.S. does not seem to adequately represent the behavior of the low copper steels used in the Belgian units and tend to underestimate the Charpy shift. This underestimation is not systematic, but it is nevertheless clear that this new formula does not bring an improvement for this class of materials, although it is conceptually more attractive because it is based on the present physical understanding of the embrittlement mechanisms. The Master Curve approach was applied on fracture toughness measurements performed on some steels that were affected by specific problems in the regulatory evaluation, or just to check the conservatism of this evaluation. It can be shown the shift of the T_0 temperature is generally comparable to the RT_(NDT) shift. In terms of fracture toughness evaluation in irradiated condition, the Master Curve makes it possible to use a direct measurement, affected by uncertainties that are much smaller than the combined uncertainties of the regulatory approach (initial RT_(NDT) + Charpy shift). It can be shown that in some cases the conservatism of the regulatory approach is very large. Even if these results are not used directly in the regulatory approach they are important in a "defence in depth" philosophy to demonstrate that, in some cases, there exist very large margins in the current approach explaining apparent outlier behaviour. The "advanced surveillance" approach, combining fracture toughness measurements with other advanced techniques like modelling, generalized load diagram and microstructural evaluation, improves our understanding in the RPV material behaviour and evolution and provides and increased confidence in the results that are obtained in the surveillance program. It therefore contributes in an important way to the safety of operation of the Belgian units.
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