Feasibility Study of Supercritical Light Water Cooled Fast Reactors for Actinide Burning and Electric Power Production

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Feasibility Study of Supercritical Light Water
Cooled Fast Reactors for Actinide Burning and
Electric Power Production NERI program funded
by the U.S. Department of Energy Idaho National
Energy Engineering Laboratory Massachusetts
Institute of Technology University of
Michigan Westinghouse Corporation
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Task 2 Fuel Cladding and Structural Material
Corrosion and Stress Corrosion Cracking
Studies S. TeysseyreJ. McKinley, Y. Yi, B.
Krieger, and G. S.Was, UM B. Mitton and R.
Latanision, MIT

• Identification of most promising candidate
  alloys for fuel cladding and core internal
  structures.
• Design and construction of an out-of-pile SCW
  loop for SCC experiments.
• Assess corrosion (MIT) and SCC (UM) of
  candidate alloys.
• Assess radiation stability and SCC
  susceptibility of candidate alloys.
• Modeling of corrosion and SCC in supercritical
  water.

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U-M SCW System Capability
Temperature and Pressure maximum 550C at 34.5
MPa Conductivity Lower than 0.1
mS/cm Dissolved oxygen Below 10 ppb - above 20
ppm Flow rate 10 - 100 ml/min
Oxygen content and conductivity are monitored at
room temperature and atmospheric pressure in both
the inlet and outlet line
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Materials
Austenitic Stainless Steels 316L and 304L
316L 1100C20min WQ grain size 44 mm 304L
as-received condition grain size 40 mm
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Constant Extension Rate Tensile (CERT) Experiments
Environment SCW (500C or 550C and 25 MPa) or
Ar Conductivity lt0.1 mS/cm Oxygen non-deaerat
ed or deaerated to lt10 ppb Strain rate 3 x
10-7 s-1 Flow rate 10-100 ml/min
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Results summary
The strain rate was 1 x 10-6 s-1 for the first
4.25 strain and 5 x 10-7 s-1 for the balance of
the experiment. Test was stopped prior to
failure
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Stress-strain behavior
316L
304L
500ºC, Argon Strain rate 3 x 10-7 s-1
500ºC, 25.5 MPa, deaerated water Conductivity
lt0.1 mS/cm Strain rate 3 x 10-7 s-1
500ºC, 25.5 MPa Deaerated water Conductivity
lt0.1 mS/cm Strain rate 3 x 10-7 s-1
550ºC, 25.5 MPa Non-deaerated water Conductivity
lt0.4 mS/cm Strain rate 5 x 10-7 s-1
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304L in non-deaerated SCW

• Minimal necking
• Intergranular surface cracks

• Ductile rupture initiated by intergranular
  fracture

Ductile Rupture
Intergranular fracture
Alloy 304L is susceptible to intergranular stress
corrosion cracking in 550C non-deaerated
supercritical water
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Influence of oxygen content on cracks density in
304L
304L sample strained to failure in non-deaerated
SCW Cracks density ? 20 cracks/mm2
304L sample strained to 25 in deaerated
SCW Cracks density ? 7 cracks/mm2
Intergranular cracks in both Non-deaerated and
deaerated SCW conditions
The lower oxygen content used for the deaerated
sample resulted in a less oxidizing environment
and may be the cause of the lower crack density.
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Behavior of 304L
The heat of 304L used in these experiments was
also tested in BWR normal water chemistry
(30 samples) 288C, pHRT6.0, cond.
lt0.2mS/cm, 2 ppm O2, 160 mVSHE PWR water
chemistry (8 samples) 320C, pHRT6.5,
cond. 20mS/cm, lt5 ppb O2, 32.5 cc/kg H2,
1000 ppm B, 2 ppm Li, -770 mVSHE Under neither
of these conditions was IG cracking ever observed
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Influence of alloy type in deaerated SCW
304L 25 strained
316L Strained to failure

• Necking similar to that in argon
• Cracks in the oxide layer
• Ductile rupture

Intergranular cracks appear on the gages
Alloy 316L does not display evidence of
intergranular cracking
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316L in deaerated SCW
Significant necking in the fracture surface
Completely ductile fracture
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Oxide formation in deaerated SCW

Both qualitative measurements indicate iron oxide
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Oxide formation in non-deaerated and deaerated SCW
Oxide composition (wt and at)
O O C C Cr Cr Ni Ni Fe Fe
wt at wt at wt at wt at wt at
304-non deaerated SCW 22 45 4 12 17 11 2.4 1.4 57 34
304-deaerated SCW 19 43 1.3 4 8.7 6 3.5 2.2 70 46
316-deaerated SCW 17 36 6 17 6 3.5 3.5 2.0 68 41
Alloy composition (wt)
C Cr Ni Fe
304L-alloy 0.035 18.3 8.5 71
316L-alloy 0.022 16.62 10.12 70
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Future Work
Analysis of oxide on four CERT samples -
thickness (SEM of cross sections) - composition
(EDS, XPS) - phase identification (XPS, XRD)
CERT tests on nickel-base alloys (Inconel 690 and
625) Irradiation of stainless steels and
nickel-base alloys to 5 dpa Analysis of
radiation damage microstructure SCC tests on
irradiated 304L SS, 316L SS, 625 and 690 in
500C, deaerated SCW Ferritic-martensitic
alloys - T-91 and HT9