Diapositive 1

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
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
  gt 380C)
• Low Ni content a priori good compatibility
  with Pb-Bi

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
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
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

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 (230C) for doses lt 8-9 dpa

DBTT shift/dpa for martensitic steels irradiated
in a spallation environment Dai et al. JNM 356
(2006) 308
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 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

Brittle failure risk (due to irradiation effects
alone) is very low
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.

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 ?K 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
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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 250C in LBE (Dai et al.)

In LBE _at_ 250C

• 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
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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