Development of an innovative corrosion monitoring methodology for the French radioactive waste disposal application

摘要

The Industrial Centre for Geological Disposal (Cigéo1) is the French project for a deep disposalfacility for radioactive waste. It is designed to dispose of high-level waste (HLW) and intermediatelevel long-lived radioactive waste (ILA-LL). The facility will operate for about a hundred years; timeduring which the integrity of the structure should be closely monitored and surveyed (i.e.reversibility period). For HLW, disposal cells consist of micro-tunnels (see Fig. 1). Cigéo's design isbased on the use of proven materials, of which carbon steel materials play a vital role from asafety assessment point of view.This concept involves multiple successive barriers: first, the vitrified radioactive waste (1) that isconfined within a stainless-steel container (2). This “primary package” is overpacked with a carbonsteel container (3). Secondly, this radioactive package is hosted in a dead-end micro tunnelconstituted by a carbon steel casing (API 5L X65 grade) (4) surrounded by a layer of a cementgrout (5) that is finally in contact with the geological Callovo-Oxfordian claystone (6).On the other hand, SCCoDRa2 (French acronym for “Monitoring of metallic components corrosionfor radioactive waste disposal”) is a 4 year industrial project that focuses on the development ofinnovative corrosion monitoring tools for CIGEO, in order to detect and monitor the corrosion of thecarbon steel casing of the micro-tunnels disposal for HLW facility.SCCoDRa monitoring approach consists in gathering innovative technologies from the fields ofNDT (Non-DestructiveTesting), electrochemistry and electrical drop-potential techniques.The adopted approach of SCCoDRa project consists in a three step-program starting with thechoice of dedicated monitoring techniques followed by the development of those techniques andfinally the validation on reduced models. The specificity of the project relies on the ability to detectand monitor a wide range of corrosion mechanisms (uniform corrosion, pitting, crevice corrosion,SCC…) and kinetics over very long-time scale in a highly radioactive environment with highgeometric limitations for sensors installation.The first phase of the project achieved in the selection of techniques to constitute a completemonitoring system: Guide Waves Tomography (GWT), Acoustic Emission, electrochemical probes(Linear Polarization Resistances, Electrochemical Noise), Distributed Open circuit potentialmeasurements and electrical resistances sensors. The coupling of such techniques should provideboth qualitative and quantitative information of the two sides of the casing (external and internal)and considering the wide range of expected corrosion mechanisms during the reversibility period(100 years).