Irradiation-resistant austenitic steels

Irradiation-resistant austenitic steels as core materials for Generation IV nuclear reactors... 

The objective of this chapter is to present an update on the progress carried out on the knowledge of the irradiation-resistant austenitic steels used as core structural materials of Generation IV systems. In the following we will focus on the SFR core materials because it is in these reactors that irradiation-resistant austenitic steels are mostly used and because the experience feedback is the most important. 

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. 

In this chapter devoted to the irradiation-resistant austenitic steels for core applications in the Generation IV reactors, we focus on the SFR core materials because this type of material has been almost exclusively used in this type of reactor which was the subject of many developments and thus, because it is of important international feedback. 

RIS in austenitic steels has been well studied. For example, in irradiated 304 stainless steel, the Cr that is added for corrosion resistance can be depleted at grain boundaries, while elements such as Ni and Si are enriched [32]. This can change the composition of grain boundaries and change their corrosion response. Fig. 7.9 shows a typical RIS profile for Cr, Ni, and minor elements at the grain boundary of a neutron-irradiated stainless steel [22,33]. At 290—310°C, the depletion of Cr and enrichment of... 

For austenitic steels, correlations between resistance to swelling and the stability of austenite were suggested as early as the 1970s to explain the large diversify in the behavior of this class of materials. Johnston [35] clearly demonstrated the beneficial effect of Ni between 15% and 60% and conversely the harmful effect of Cr between 7% and 30% on the resistance to swelling of ternary alloys by strong ion irradiation doses (see Fig. 8.13(a)). 

Of the three stabilizing candidates generally studied (Ti, Nb, and V), Ti is the element that has the greatest influence on the swelling resistance of austenitic steels under neutron irradiation. To describe the role played by this element, Fig. 8.16(a) compares strains (essentially due to swelling) observed on Phenix fissile pins clad with four different grades (316 and 316Ti steels used in two states, solution annealed, and... 

Teysseyre et al. [125] reported that the density of cracks and crack depth for austenitic stainless steels preirradiated up to 7 dpa increased over the unirradiated case in SCW at 400°C. Under the same irradiation and test conditions, ferritic-martensitic alloys were found to be resistant to cracking. 

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