Corrosion monitoring programs at Slovak's nuclear power plants

摘要

Monitoring of corrosion stability of safety related components is an important task for the safety operation and lifetime extension of NPPs. From the operational experience and from the demands of the national regulatory bodies follows requirements for corrosion behaviour monitoring of main structural materials. As the respond to this requirement, several technical solutions have been prepared for the long-term monitoring of NPP materials. The monitoring systems described in this paper are based on the principle of surveillance samples. All specimens made from original materials are placed into the original environment and loaded with stresses similar to the operational ones. Following monitoring systems are under operation: Corrosion loops in primary circuit are the unique equipment that have been installed in primary circuits of Bohunice Unit-3 NPP and Mochovce Unit-1 NPP and provide the possibility to expose sets of samples in original conditions. For Mochovce Unit 3 and 4 there are prepared new corros ion loops. Corrosion monitoring systems placed in interim spent fuel storage pools. The spent fuel interim storage in the NPP Jaslovske Bohunice makes use a wet storing, i.e. the spent fuel assemblies, which are placed in racks, are stored in large water pools. Sets of samples are placed into each water pools and periodically evaluated. Corrosion monitoring system installed into the large underground tank used for storing of liquid radioactive waste. In past there were operated two monitoring systems installed at V-l NPP: Monitoring system on the primary flange of the steam-generator collector enabled a long-term exposition of various samples inside the steam generator above the primary collector flange in secondary circuit conditions. Inside of the water shielding tank around reactor pressure vessel, which was typical construction of V-l NPP, there were placed for several years a specific corrosion monitoring system. Corrosion monitoring systems provide important information about corrosion situation of both materials and equipment. From the corrosion point of view and obtained results it is possible to state, that used structural materials are stable in given standard condition and make possible to extend the lifetime of NPPs.