Specific wear of Rod Cluster Control Assemblies (RCCA) in Pressurized Water nuclear Reactors (PWR) results from contacts with their guides due to flow induced vibration. Particular sliding impact contact conditions and specific environment in PWR coupling temperature and solution chemistry involve original mechanisms of wear. A specific tribometer has been developed during these past years by FRAMATOME-ANP. This simulator operates in experimental conditions close to sliding impact motion of RCCA assemblies against guides and under similar environment (temperature, pressure and water chemistry). Numerous and various wear tests were realised in order to study the influence of the sliding impact parameters on wear loss and wear scars. Specific tests with continuous data acquisition were realised. Different wear scars were observed. An analogy with erosion was done. An erosion model was used to determine critical conditions concerning friction coefficient and incidence angle values leading to wear. Considering these critical conditions, it was possible to explain the observed difference of wear loss and facies.