1. 1 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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

2. 2 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 MEGAPIE target : The structural Materials 3 main materials were used in the MEGAPIE Target :  AlMg 3 : 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

3. 3 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 Beam window of the safety hull of SINQ Target-3 after cutting of discs at 3 postions Dai et al. JNM 343 (2005) 184 The AlMg 3 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 AlMg 3 LTE should not cause any problem up to the end of the MEGAPIE operation (expected proton charge ~ 3 Ah)

4. 4 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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) The 316L components should safely operate up to the maximum envisaged proton charge Saito et al. JNM 343 (2005) 253 Kalkhof et al. JNM 318 (2003) 143

5. 5 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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

6. 6 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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

7. 7 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 Risk of Brittle failure 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 Toughness for T91 irradiated in a spallation environment (Dai & Maloy) Stress Intensity factor for a large surface crack as a function of crack depth Brittle failure risk (due to irradiation effects alone) is very low

8. 8 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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.

9. 9 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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 J-B. Vogt et al. Eurocorr 2005 Very low probability that a deep crack (a few tenths of mm depth) would form on the window inner surface

10. 10 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 Risk of Brittle failure in LBE The toughness of T91 irradiated to 9 dpa was determined at 250°C in LBE (Dai et al.) Toughness for T91 irradiated in a spallation environment (Dai & Maloy) Stress Intensity factor for a large surface crack as a function of crack depth 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

11. 11 MEGAPIE Structural Materials : Is there a risk of failure? MEGAPIE Workshop Aix-en Provence, Nov. 2006 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