EDF Project – FIB ‐ SEM nuclearized for investigations in a hot cell on irradiated materials

Abstract

Context: CEIDRE laboratory (Centre d'Expertise et d'Inspection dans les Domaines de la Réalisation et d'Exploitation) based at EDF Chinon Nuclear Power Plant, is in charge of expertising and monitoring. Results of analytical studies bring to better understand the rate of ageing phenomena on power production installations; in addition it is contributing in improving and making safely reliable the exploitation and maintenance strategies in the electricity production subject. Investigations are performed thanks of various analytical techniques as : Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) or Castaing microprobe (EPMA). It allows to multi scale images and analyses the damages caused by material ageing during its service (ageing under radiations or under heating, corrosion under load, mechanical breaking). At the ultimate level, the use of a TEM is requesting a specific sample preparation, so called TEM lamella with manual bring to state techniques into hot cell preparation units. The manipulations of such radioactive materials are today outdated by the current regulation regarding safety rules and some new performances of thinning the samples are now needed. In order to limit these risks, the CEIDRE lab has invested into a new system, a Focused Ion Beam (FIB) dedicated to extract thin TEM lamella from a bulk sample. The FIB is coupled with a SEM column, an Energy Dispersive Spectrometer (EDS) and a Time of Flight Spectrometer (TOF SIMS) for elementary analysis and chemical mappings. Complementary to conventional preparation techniques, this tool is also enlarging the previous SEM capacity with fractography, chemical and crystallography analysis. This modern technique is now installed into a hot activity cell and allows the capabilities to operate on active materials. Specific conception is mandatory to make operational this tool in such severe conditions; however the system is based from standard components where challenging points must be considered: Sample loading and unloading via tele manipulators arms without damaging the FIB/SEM motorized stage and Remote operations of many (as much as possible) of driving units that cannot sit into the cell. The entire project has been in trust to ELOÏSE sarl associated with NewTec Scientific companies, a TESCAN LYRA 3 GM. From 2013 to 2015, the system has been rebuilt under NewTec laboratories in Nîmes France, commissioned and finally installed in its final destination into a cell at LIDEC (Laboratoire Intégré d'Expertise du CEIDRE). Modifications – Features : From the strong environmental conditions (gamma activity, acoustic, thermal and mechanical), the instrument plus its accessories have been totally deconstructed and rebuilt to fits the requested exigencies. Most of the electronics units dedicated to the control of the instrument and its accessories (micromanipulator, EDS and TOF spectrometers) are relocated in the so called front zone , 10 meters away from any radiation and outside the hot cell. Most of the cables have been rebuilt and requalified to over Giga Ohms range. In cell, sensitive components are now fitted with enhanced protection against radiation. Based on feedback systemic studies have been proceed with various known critical scenarios, then new solutions came from that analysis. The EDS spectrometer received a tungsten base shielding offering a deep protection against emissive rays coming from the samples. In case of major failure of the instrument, an emergency routine composed by a tele manipulate‐able tool and a in chamber toboggan allows to collect the sample holder. Finally a semi‐automatic loading station has been totally built around the original instrument. This work has been carefully study regarding the specific ergonomy and way of manipulating the samples entering the hot cell (remoted display and three buttons easy to use panel). Résults & Perspectives : As far as today, the outside cell units escape is confirmed as the best strategy in retailoring an instrument to operate safely. This includes reconsidering signal to signal treatment (e.g. use of optical fibers for communications). However, and despite the massive modifications done, the system is keeping the original performances for both SEM & FIB capabilities. Beyond this points, the high speed networks available at EDF allows extreme safe and comfortable operations even on critical samples. This tool is now fully operational, the next challenge is human. Training and transmit to operators the new way of tele‐working the SEM/FIB.