Analysis of mechanisms induced by sliding and corrosion: dedicatedapparatus for PWR environments

摘要

In pressurized water reactors (PWR), some components are submitted to relative motions duernto necessary operational processes (localisation and positioning adjustment) or by not wishedrneffects (flow induced vibration). Thus, components and associated supports are typicallyrnexcited by a large range of kinematics so than complex combinations of wear can occur.rnThose excitations can lead to sliding, fretting, impact…rnFurthermore, typical environment in PWR coupling of temperature (320℃), pressure (154rnbars) and chemistry solution (deaereted, low conductivity water) involve specific corrosionrnprocesses.rnApparently, research performed to date did not deal with all the specific parameters involvedrnat PWR conditions. For this purpose, a specific apparatus has been developed in FramatomernTechnical Center for a better understanding of this complex degradation mechanism wherernmechanical and corrosion effects are occurring at the same time.rnThanks to electromagnets excitation, mechanical investigations can be proposed with thernfollowing combined contact type: pure impact, pure sliding and impact plus sliding for severalrnkinds of sample as rod in a ring, rod against a guide. Motion can be induced on a local area orrnfor the total length (orbital excitation). The relative displacement and the contact force arernacquired continuously and permit to establish normal and tangential forces, angular position,rnsliding distance.rnOn the other hand, electrochemistry measurements have been adapted to the specificrnapparatus and work in the high temperature water environment. The standard mounting withrnthree electrodes has been qualified so that it is possible to adjust or measure current andrnpotential.rnAll the system is computer controlled and with the present apparatus relationship betweenrnmechanical parameters and repassivation can be studied for specific environments, materialsrnand solicitations.rnIn a first step, potential dynamic polarization curves have been established for 304L stainlessrnsteel at several temperatures (80, 250 and 300℃) and for different initial pre polarizationrn(level, duration…)rnIn a second step, scratch test indentation between non conductive sample and stainless steelrnhas been carried out to qualify all the experimental design.rnFinally, investigations were performed for different loading (impact, impact plus sliding andrnsliding) at several levels of forces. Effect of time latency has also been investigated.