Advanced austenitic materials

Fig. 8.4 highlights the fact that, beyond the material nature, the key parameter governing the Fe dissolution is here the Cr content starting from 9% in the ferrito-martensitic EMI 2, which is therefore unsuitable for reprocessing with classical processes, to 16% with the 316 type steels which present no reprocessing problem at all. In Section 8.6 we discuss the possibility of specifying an advanced austenitic steel exhibiting a lower Cr content than classical materials of 300-series, and will have to keep in mind the rather poor behavior of the 12% Cr N9 material, CEA precursor of advanced austenitic materials. 

Development of advanced austenitic materials designed to increase the in-pile duration of core structures of Generation IV systems... 

In the meantime, the Americans abandoned the R D on SFR and the main remaining potential advanced austenitic material for cladding application was the D9 (Table 8.2 and Fig. 8.21) and its derivatives (Table 8.3), the D91 (with special... 

Figure 8.23 Volume swelling of advanced austenitic materials irradiated in the SUPERNOVA capsule up to 88 dpa in Phenix [61].

It seems that, beyond the progresses realized from the first 300-series steels to the present reference materials (15-15Ti and D9 derivatives), it would be possible to find an ultimate upgrade in the family of irradiation-resistant austenitic steels using a CW 12-15/15-25 Ti + Nb stabilized and P-doped matrix, but further work has yet to be done to specify the content of other alloying elements (Mo, Mn, C, Si, N, B) and to adjust the fabrication route to optimize the in-pile behavior of such advanced austenitic material for high-dose applications. 

The PIE of fuel subassemblies of PNC316 steel and PNC 1520 advanced austenitic stainless steel inadiated in FFTF has been successfully completed. The 2nd shipment of irradiated fuel materials to OEC was conducted to take a further investigation of high bumup fuel behavior. 

PNC1520 advanced austenitic steel was developed for high burnup FBR fuels. Excellent performance is demonstrated by the out-of-reacter and material irradiation testing programs. Design base standard of PNC1520 is completed and evaluation study is in progress to apply Monju and DFBR cotes. 

Figure 6.32 Comparison between experimental lifetimes and predicted ones. The necking model is used at high stress whereas the Riedel intergranular damage is used at low stress (high-stress regime of strain rates) and very low stress (low-stress regime of strain rates), (a) Material A (b) material B. Experimental data found in Ref [103]. Advanced austenitic stainless steel, Fe35Ni25CrNb, 980°C.

Table 8.3 lists the main advanced austenitic steels studied in Western countries and Japan to increase the in-pile properties of fast core structures beyond the present reference materials. 

In terms of R D on advanced austenihc materials for the fast fuel subassembly and as part of the European Fast Reactor (EFR) project, European work done on austenitics... 

The sweUing of austenitic materials limits their application to intermediate doses (up to 100/150 displacements per atom (dpa)), whereas F-M ODS materials appear as the most advanced materials to reach higher doses well above 150 dpa. 

One of the fuel rod designs is summarized in Table 2.23 [34] and compared with those of a typical BWR and PWR. In the case of this design, the cladding material needs to withstand the stress of —64 to +71 MPa at a temperature of 757°C for the period of 36,000 8,000 h (500 days multiplied by 3 cycles). Some advanced austenitic stainless steels, such as PNC 1520 of the former Japan Nuclear Cycle Development Institute (INC) may be able to meet such requirement. 

All processes still require use of oxygen for pasava-tion in the synthesis loop. Metallurgical advances have reduced the amount required. Snamprogetti now utilizes a bimetallic zirconium/25-22-2 (Ni, Cr, Mo) tube in its stripper. The corrosion rate for zirconium in urea service is nil. Toyo utilizes a duplex alloy (ferrite-austenite), which requires less ojqjgen. Stamicarbon working with the Swedish steel producer Sandvik, has patented a proprietary material called Saferex, which requires very little oxygen future plants wnll use this new material,... 

Klar, E. and Samal, P. K., "Effect of Density and Sintering Variables on the Corrosion Resistance of Austenitic Stainless Steels, Advances in Powder Metallurgy and Particulate Materials, MPIF, Vol. 3, 1996, pp. 11-3 to 11-17. 

This chapter will discuss the macroscopic and microscopic properties of Generation IV reactor materials, and the advances in characterization of irradiation-induced defects and in mesoscale modeling of irradiation damage. The majority of the examples provided are based on ferritic-martensitic (F-M) steels, even though they might not always be primary candidates for Generation IV reactors, but the reported defects and microstmctural features are typical of other irradiated alloys, and F-M steels are used as an illustrative example. In some cases, comparisons will be made to austenitic steels to illustrate how differences in crystal stmcture and alloy composition can cause large differences in radiation response. 

The Ti-stabiUzed N9 material, the precursor of advanced low Cr/high Ni austenitic bases, has been tested in the Phenix BACCHUS program comprising several subassemblies but only the BACCHUS 1 bundle irradiated up to 109 dpa has been examined. Its chemical composition (Table 8.3) is relatively well optimized but the content of major elements Cr and Ni could be further refined to give a better behavior in its enviromnent (Cr probably too low) and its structural stability under irradiation (Ni probably too high). It could also be improved in terms of the minor elements, particularly phos-phoras, that should be increased, and possibly nitrogen. 

Austenitic stainless steels are a class of materials that are extremely relevant for conventional and advanced reactor technologies. They are Fe-Cr-Ni alloys with a fully or quasifuUy face-centered-cubic close-packed crystal structure which imparts most of their physical and mechanical properties [7]. Various chemical additions enhance their properties over a wide range of temperatures. Three main alloy classes are to be considered here 304, 316, and alloy 800 series. 

Recent Advances in Metal-Based Materials The use of shape-memory alloy (SMA) reinforcements is very promising in retrofit and strengthening of existing structures. SMAs have more than one crystal structure. This is called polymorphism. The prevailing crystal structure or phase in polycrystalline metals depends on both temperature and external stress. They are a class of metallic alloys that can remember their initial geometry during transformations (forward and reverse) between two main phases at their atomic level (austenite and martensite). 

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