Irradiation Behaviour of Three Candidate Structural Materials for ADS Systems: EM10, T91 And HT9 (Ferritic/Martensitic Steels)

E. Lucon (Sp), A. Al Mazouzi, SCK-CEN, Moll (Belgium) 
High Chromium ferritic/martensitic (F/M) steels are presently considered as potentially the most promising structural materials for Accelerator Driven Systems (ADS), on account of the severe expected service conditions, namely significant hardening and embrittlement caused by both neutron irradiation and production of spallation elements. In the framework of the EC FP5 project SPIRE, three conventional F/M steels have been irradiated at 200 °C in the BR2 reactor of Mol up to approximately 4.5 dpa: 9Cr1Mo (EM10), 9Cr1MoVNb (T91) and 12Cr1MoVW (HT9). The effects of neutron irradiation on their mechanical properties have been investigated both in terms of hardening (increase of tensile strength) and embrittlement (shift of DBTT and decrease of USE), by performing post-irradiation tensile, Charpy impact and fracture toughness tests. Results of the PIE will be presented, as well as comparisons with the unirradiated condition.
It was observed that the two 9Cr steels have a similar response to irradiation, with EM10 being however somewhat tougher than T91 in both unirradiated and irradiated condition; HT9 shows very pronounced hardening and embrittlement, as expected on the basis of its higher Cr content. Two issues, potentially relevant in view of both plant design and safety-related aspects, have been identified: the magnitude of the irradiation-induced transition temperature shift (systematically larger when measured from toughness tests than when estimated from Charpy impact results) and the questionable applicability of the Master Curve approach to this class of materials.

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