For western pressure vessel reactors, assessment of pressure vessel steels irradiation embrittlement due to neutron irradiation is based on a semi-empirical formulae which predicts the shift of a reference lower bound fracture toughness curve as a function of fluence and embrittlement-involved chemical elements. Periodically, in order to monitor the embrittlement of each RPV, the predictions of the formulae is confronted to experimental results obtained from Charpy specimens located in surveillance capsules irradiated with a higher fluence level than the pressure vessel itself. Historically only the shift of the temperature index defined for a given level of energy, e.g. 56J in the French surveillance program, is used. In support to the French surveillance program methodology, for some of the French RPVs, physical models of fracture (for both cleavage and ductile fracture) are used to analyse in details the whole experimental basis available at different levels of fluence. This study presents the methodology developed in order to analyse the experimental results of a RPV steel from the french surveillance program, including Charpy and fracture toughness tests at different levels of fluence i.e. of embrittlement. The methodology applied aims to use the numerous Charpy tests results available in order to assess, at the same fluence levels, the fracture toughness embrittlement. The results are then compared to available fracture toughness results for a given level of embrittlement.

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Coatings of silicon rich silicon carbide are obtained in a plasma assisted device from tetramethylsilane and argon mixture, around 760K under reduced pressure on metallic alloys: FeCrAl and NiCrA1.The atomic composition of the deposits is determined by microprobe analysis and adherence is evaluated by scratch test measurements. These results are discussed in relation with previous determinations obtained when identical films are deposited on low carbon steel substrates. All samples exhibit a similar behavior which denotes a good adherence. The formation of a diffusion zone is responsible for this trend. The qualitative behavior of the coated substrate in air at high temperature (1273 K) is investigated in comparison with the uncoated substrate through cross section examinations by different analysis (EDS mapping, WDS profiles). The heat treatment (lOh, 100h) induces a strong diffusion which is discussed. It is evidenced that the silicon carbide based films drastically change the oxidation mechanism (mainly in the case of NiCrAl) and tend to improve the resistance of the substrate against an oxidizing atmosphere. Futhermore, some solutions to improve the lifetime of such metallceramic junctions are suggested. As for example, the interest of an alumina interlayer between S i c coating and FeCrAl substrate is experimentally shown.

Abstract. -We have studied the oxidation behaviour ofthree industrial Fe-Cr-A1 alloys (with or without yttrium) at temperatures ranging between 1200 and 1350 "C. At 1200 OC, the behaviour of these alloys is improved as the yttrium content rises. However, for temperatures higher or equal to 1300 "C, the presence of yttrium seems to be detrimental. In particular, the distribution of this element in YFe9 or Y2FeI7 intermetallic particles allows yttrium to diffuse towards the surface of the product. The high kinetic of this diffusion leads to the formation of oxidized cavities by Kirkendall effect. The results obtained on the 0.14%-yttrium product show that the distribution of this element under the oxidized form could help to avoid this damage.

The oxidation behaviour of four industrial Fe-Cr-Al alloys was studied. Two of them were Fe-Cr-Al alloys fabricated either by melting or by powder metallurgy. The two other ones were Fe-Cr-Al-Y alloys either produced by melting or by mechanical alloying. On these alloys, we determined oxidation kinetics and observed the morphology of the oxide layer after isothermal and cyclic exposures from 1000°C up to 1300°C. The beneficial effect of yttrium on the adherence of oxide layers was confirmed. The powder metallurgy fabrication route does not improve the oxidation resistance of yttrium-free alloys. On the other hand, the association of the powder metallurgy and the addition of yttrium allow the manufacturing of alloys which present an excellent behaviour to high temperature oxidation