MANUFACTURING CONDITIONS OF FRENCH REACTOR PRESSURE VESSELS TO AVOID THE OCCURRENCE OF HYDROGEN FLAKES

摘要

The formation of hydrogen flakes in Reactor Pressure Vessels (RPV's) forgings is a well known phenomenon that can affect forging components during manufacturing. Following recent data from Belgium, it has been the object of important assessments during the last 3 years. We will present in this paper elements pertaining to the RPV's of the French nuclear fleet. A thorough review of fabrication processes and specifically of ultrasonic examination of forgings, including the oldest ones has demonstrated that the risk of leaving undetected hydrogen flakes in RPV's forgings is not a problem in French RPVs. The French Regulator also clearly shared this position point in 1985. Parts with defects were once again observed at the beginning of 2012 but the defects were attributed to errors in hydrogen measurement at the steel maker shop. Those hydrogen induced defects were detected at an early manufacturing stage (before quality heat treatment) by ultrasonic examination, and the concerned parts were consequently rejected through the normal quality control process.