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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?

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

slide2

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

slide3

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

slide4

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

slide5

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

slide6

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

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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

slide8

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

slide9

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

slide10

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

slide11

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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