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MEGAPIE Structural Materials Is there a risk of failure?

MEGAPIE Structural Materials Is there a risk of failure?. J. Henry & J. Konys For the X7-X10 Working Group : A. Almazouzi, T. Auger, Y. Dai, A. Gessi, H. Glasbrenner, D. Gorse, F. Gröschel, I. Serre, A. Terlain, J-B. Vogt. MEGAPIE target : The structural Materials.

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MEGAPIE Structural Materials Is there a risk of failure?

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  1. MEGAPIE Structural Materials Is there a risk of failure? J. Henry & J. Konys For the X7-X10 Working Group : A. Almazouzi, T. Auger, Y. Dai, A. Gessi, H. Glasbrenner, D. Gorse, F. Gröschel, I. Serre, A. Terlain, J-B. Vogt MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  2. MEGAPIE target : The structural Materials • 3 main materials were used in the MEGAPIE Target : •  AlMg3 : Lower Target Enclosure (LTE) • T91 : Lower Liquid Metal Container (LLMC) & Beam Window (BW) • 316L Stainless Steel : Other parts such as the Flow Guide Tube (FGT), By-Pass Flow Tube (BFT), Fill and Drain Tube (FDT), Central Rod (CR), Electro-Magnetic Pump, Heat exchanger… • Reasons for the choice of T91 for LLMC : • Very good thermomechanical properties (High strength, low thermal expansion, high thermal conductivity) • Excellent radiation resistance (at temperatures > 380°C) • Low Ni content : a priori good compatibility with Pb-Bi MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  3. The AlMg3 Lower Target Enclosure • AlMg3 safety Hulls have been used for all SINQ solid targets : •  Two were operated without problem up to more than 10 Ah proton charge • Two others reached more than 6 Ah The MEGAPIE AlMg3 LTE should not cause any problem up to the end of the MEGAPIE operation (expected proton charge ~ 3 Ah) Dai et al. JNM 343 (2005) 184 Beam window of the safety hull of SINQ Target-3 after cutting of discs at 3 postions MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  4. The 316L Internal Structures • These structures will experience no or moderate irradiation (peak damage for a 3Ah proton charge about 2.5 dpa) : Given these irradiation condition and the operating temperature range, 316 L will retain significant, ductility, toughness and fatigue resistance • low corrosion rate, evaluated to be in the relevant T range at low oxygen content/in flowing LBE ~0.1 mm/year • Low cycle fatigue life of 316L in LBE little affected compared to results in air • Maximum stresses in the irradiated parts relatively low (Von Mises eq stress about 60-70 MPa) Saito et al. JNM 343 (2005) 253 The 316L components should safely operate up to the maximum envisaged proton charge Kalkhof et al. JNM 318 (2003) 143 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  5. The Lower Liquid Metal Enclosure and Beam Window • The LLME and in particular the Beam Window is the most critical component • Multiple causes of damage/ acting synergistically : • corrosion/erosion by flowing LBE • Irradiation embrittlement by energetic protons & neutrons • Liquid Metal Embrittlement (LME)/Liquid Metal Accelerated damage (LMAD) • Cyclic Mechanical/Thermal loadings MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  6. Irradiation-induced embrittlement of T91 irradiated in a spallation environment • Irradiation in a spallation environment induces a large DBTT shift at low temperature • However the Ductile –to-Brittle Transition temperature was evaluated to remain below the hot stand-by temperature (230°C) for doses < 8-9 dpa DBTT shift/dpa for martensitic steels irradiated in a spallation environment Dai et al. JNM 356 (2006) 308 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  7. Risk of Brittle failure Toughness for T91 irradiated in a spallation environment (Dai & Maloy) Stress Intensity factor for a large surface crack as a function of crack depth • The toughness remains significant up to 8-9 dpa at 250°C • Due to the low stress value in the window, the K value far below the retained toughness even for a large & deep surface crack Brittle failure risk (due to irradiation effects alone) is very low MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  8. What about LME/LMAD? • T91 was shown to be prone to LME if there is plastic deformation and intimate contact with the liquid metal • Such conditions not encountered at the beginning of operation : • absence of plastic deformation : T91 has high strength, increased by the irradiation, and stresses are low • presence of native oxide which should prevent wetting during preconditionning/start up procedure • LISOR results have shown that an oxide layer (i.e. additional protection against wetting) should form on the surface irradiated by the proton beam • However, the oxygen content in Pb-Bi is expected to slowly decrease during operation (unknown rate) : • Dissolution of the protective oxide layer ? • Intergranular attack ? It is a concern since it was shown that intergranular attack can play the role of crack initiation sites which may propagate by cyclic loading in LBE leading to a reduction of the low cycle fatigue life. MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  9. Formation of a fatigue crack on the window surface? • The general trend is that the reduction in fatigue life in LBE /air disappears at low stress/strain values, which is the case for the MEGAPIE window • If a small crack were to form, its growth rate would be very small due to the low ΔK range Very low probability that a deep crack (a few tenths of mm depth) would form on the window inner surface J-B. Vogt et al. Eurocorr 2005 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  10. Risk of Brittle failure in LBE Toughness for T91 irradiated in a spallation environment (Dai & Maloy) • The toughness of T91 irradiated to 9 dpa was determined at 250°C in LBE (Dai et al.) In LBE @ 250°C • Even if a deep surface crack were to form, the LEFM analysis still predicts that the risk of brittle fracture is negligible Stress Intensity factor for a large surface crack as a function of crack depth MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

  11. CONCLUSION A Failure of the Lower Liquid Metal Container is very unlikely within the service time of the target (maximum proton charge  3 Ah)under normal operating conditions MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006

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