We try to develop nondestructive methods to monitor the effects of neutron irradiation in ferritic alloys. In this paper we report results obtained with a method based on thermoelectric power (TEP). This method is already used to monitor the thermal aging of duplex stainless steels. It is shown that the measurement of the thermoelectric power allows the monitoring of the effects of i) electron irradiations on Fe-Cu model alloys, and ii) neutron irradiations on industrial pressure vessel steels. The recovery of these irradiation effects during thermal annealing can also be followed with the proposed method. On the basis of the results obtained on Fe-Cu alloys, we propose a law to determine the limit of copper solubility in α iron at temperatures below 600°C.

The evolution of the microstructure of the French Chooz A pressure vessel steel (characterized by a low copper content (<0.1 at.% Cu)) has been studied during annealing at 450°C. The irradiated material (fluence: 0.5 to 16×1023 n.m-2, flux : 2×1015 n.m-2.s-1, temperature : 275°C) shows a quick recovery of hardness after 20 h of aging. The intensity of the SANS scattered signal as well, as the thermoelectric power one, decreases with annealing time. In addition, 3D images, at the atomic scale, given by the Tomographic Atom Probe show that during the first hours of annealing, the neutron-induced Cu-Ni-Mn-Si clusters formed during the in-service irradiation are “dissolved” while copper precipitates are formed. Their low number density is in agreement with the full recovery of the hardness. These results are of primary importance for prediction of recovery of an irradiation embrittled steel and also for prediction of its behavior during reirradiation. This work also shows that the nondestructive technique, thermoelectric power, may be used to “follow” the microstructural evolution of materials during annealing treatments.

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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.