Reactor Pressure Vessel Surveillance Programs in Belgium

摘要

Reactor pressure vessel (RPV) irradiation embrittlement is monitored by means of surveillance capsules containing the RPV beltline materials that are inserted in the RPV before the start of operation. These capsules are placed at locations in which they receive a higher neutron flux than the vessel wall by a factor on the order of two to three. They are regularly retrieved and tested to evaluate RPV irradiation embrittlement according to specific regulatory procedures and standards to guarantee the safe operation of the RPV throughout its lifetime. These procedures often rely on empirical but conservative concepts. Taking advantage of the improved understanding of irradiation effects, analytical tools have been developed to improve the quality of RPV embrittlement assessment. These tools become particularly important in the case of operation beyond the original design life of 40 years. In this framework, an alternative but complementary and enhanced surveillance program assessment has been developed in Belgium that benefits from the latest developments in the area of material science and irradiation effects. By combining a few additional experimental tests and multiple property correlations supported by analytical tools, the data can be assessed in a much more consistent way than relying on the sole Charpy test and empirical correlations. The enhanced surveillance approach has previously been described, and only the main points are summarized herein, the focus being on the application to the Belgian units. The benefits of such an approach in enhancing the confidence in the surveillance results and in demonstrating the existence of additional safety margins with respect to the regulatory approach are highlighted.