Understanding the Risk of Failure in MEGAPIE Structural Materials

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. Grschel, 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 > 380C) 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 (230C) 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 250C 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 K 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 250C 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 @ 250C 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