Experiences on LeadBismuth PbLi Loops

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Experiences on Lead-Bismuth (Pb-Li) Loops

• C.M. Das, R. Fotedar
• Material Processing Divison
• BARC

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• Corrosion in Lead-Bismuth Eutectic
• Caused by high solubility of Ni, Fe and Cr in
  LBE
• Factors affecting corrosion
• Alloy composition
• Temperature
• Dissolution
• Solubility
• Diffusion

Solubility in LBE, wppm

• Flow velocity
• Temperature difference

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Static corrosion

• Determined solubility and diffusion of Ni, Fe
  and
• Cr in LBE
• Corrosion continues till saturation of LBE

Corrosion under Isothermal flow

• Mass transfer by diffusion and
• convection
• Corrosion stops after homogeneity
• is reached throughout the system

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Corrosion under Non-isothermal flow

• Dissolution of elements of steel from the
• high temperature region
• Transportation to lower temperature
• zone and precipitation
• Saturation solubility never reached
• Higher the temperature difference,
• severe is the attack in hot section.

Corrosion mitigation by oxygen control

• Low chemical reactivity of Pb and Bi
• compared to Fe, Cr, Ni

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G. Muller et al., Journal of Nuclear Materials
321 (2003) 256262

• PbO production be avoided.
• Prevent contamination
• Stable hydrodynamics
• Efficient heat transfer

2?G0 (PbO) gt RT ln pO2 gt 0.5??G0 (Fe3O4) pO2 is
oxygen partial pressure in gas equilibrium with
the molten eutectic
Dissolved oxygen concentration ? Solubility of
oxygen
EllinghamRichardson diagram For oxides of Fe,
Ni, Bi and Pb
Oxygen solubility /upper limit in LBE in wppm
(10-4 wt)
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Oxygen concentration range for LBE
Between 200 to 400 ºC 4 x 10-10 to 10-8
wt Between 400 to 600 ºC 2 x 10-7 and 10-5
wt
Oxygen control
CO ½ O2 CO2 H2 ½ O2 H2O
pO2 (pH2O/pH2)2.exp(2?GoH2O/ RT)
Processes in LBE loop
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Oxygen Measurement
Schematic of the electrochemical cell In solid
electrolyte oxygen sensor
Pb 1/3 Bi2O3(Bi) PbO(Pb) 2/3 Bi
Oxygen sensor
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OBJECTIVES

• To gain experience in handling of hot liquid
  metal
• To gain experience of filling the loop with
  molten metal under gas pressure, also to transfer
  the same in dump tank in case of emergency
• To have an overall feel of the operation of the
  system, which includes instruments, safety
  aspects and most important reliability of the
  system
• To study the long-term effects of molten
  Lead-Bismuth eutectic alloy on materials of
  construction
• Diagnostic studies for thermal hydraulic loop.

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DESIGN PHILOSOPHY

• Velocity is induced by flow.
• Flow is induced by buoyancy.
• Buoyancy force is induced by temperature
  difference.
• Large the temperature difference, mass transfer
  of material constituents takes place.
• Safe operating temperature (from corrosion view)
  was used for calculating buoyancy head.

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DESIGN OF THE LOOP

• The pressure head generated by the buoyancy is
  given by
• ?Pbuoy ß .?TH. g ?L
• where ß thermal expansion coefficient K -1
• ?TH temp. difference.
• g acceleration due to gravity.
• ?L Distance between the thermal
  centers.

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• The pressure head obtained due to buoyancy has to
  provide sufficient pressure head to overcome
• Pressure drop across the H.E
• Pressure drop across specimens.
• Pressure drop due to friction.
• Pressure drop due to circulation in the pipe.
• The height h required
• H

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• To ensure the calculated buoyancy head is
  adequate for driving the loop. Either height of
  the loop or diameter of the pipe needs to be
  increased.
• Increasing the dia. increases the LBE inventory
  and other operational difficulties.
• Manipulation with height gave the required
  buoyancy head.

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THERMAL CONVECTION LOOP
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Safety Analysis
A safety analysis for all normally foreseeable
occurrences was carried out the details are as
follows.

• LEAK BEFORE BREAK ANALYSIS. (LBB)

• In austenitic S.S systems, rupture of a
  pipe/
• pressure vessel is not expected because
  these
• are low-pressure systems contained in highly
  
• ductile materials.
• Leak before break is used in analyzing a
  failure.
• Hence at no time a sudden rupture of pipe/
• vessel is expected.

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BENDING ANALYSIS for LBB
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THERMAL CYCLING FOR LBB Analysis
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2. Fire Protection

• Liquid metal fire

• In case of double rupture the LBE shall come in
  contact with following materials.
• Ceramic Fiber
• Grade HTZ
• Melting Temp. 1760 ºC
• Max. Service temp. 1260 ºC
• Aluminum Sheet.
• Melting temp.
  600 ºC
• Active fire fighting by means of spraying
  suitable
• dry chemical powder.
• Spraying shower of pressurized air

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• Conventional Fire

• Only fires of electrical cables are
• considered under this category, as
• there is no other combustible
• materials present in and around loop
• area.
• Adequate quantity of CO2 extinguisher
• have been provided for the purpose

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LOOP WITH SAFETY FEATURES
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SCADA BASED SAFETY FEATURES

• HEATER FAILURE.
• 2. THERMOCOUPLE FAILURE
• 3. LBE LEAKAGE

• MINOR
• MAJOR

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HEATER FAILURE
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LEAK DETECTION
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OPERTING SEQUENCE

• 1. Vacuum tightness at R.T
• 2. Positive pressure tightness at R.T
• 3. Vacuum tightness at elevated temp.
• 4. Preheating of the loop without LBE
• 5. Melt LBE in melting Tank.
• 6. Clean the LBE melt.
• 7. Transfer LBE into the Dump tank.
• 8. Increase the loop temp.
• 9. Transfer the melt into the loop by gas pr.
• 10. Increase the loop leg temp.
• 11. H.E start up and adjust the temp.Diff.
• 12. Loop is operational.

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• Material SS316L
• Dimension 100 cm x 100 cm
• Diameter (ID) 12.5 mm
• Estimated Flow rate 16 cm/s
• Temperature Hot 350 / 450?C
• Cold 250 / 350?C
• Oxygen Ar 5 H2 / 7.4 ?C

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316L and 9Cr-1Mo at 350 and 450ºC for 2500 h
Weight change after exposure
Tensile test in air at 25ºC

• SS 316L resists corrosion in LBE upto 350?C
• 9Cr-1Mo steel is resistant to corrosion upto
  450?C
• Ductility of both steels increased when exposed
  to
• LBE. Higher at 450 ?C than at 350 ?C
• UTS was lowered to a large extent at 450 ?C

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Brittle fracture Laminar failure
Ductile fracture
Brittle fracture
Fractographs of SS316L(a) as-received (b) exposed
to LBE at 450?C, and 9Cr-1Mo (c) as-received
(d) exposed to LBE at 450?C
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Cross-section of SS316L exposed to LBE (a) at
350?C (b) at 450?C, and 9Cr-1Mo exposed to LBE
(c) at 350?C (d) at 450?C
No penetration of LBE into 316L or 9Cr-1Mo after
exposure
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304L at 250 and 350ºC for 3600 h

• Weight change after exposure

• At 250 ºC 3-6 mg.cm-2
• At 350 ºC 0.1-0.8 mg.cm-2

• Composition of surface film

• At 250 ºC PbO/ Bi2O3
• At 350 ºC Fe3O4/Cr2O3

• No corrosion of SS304L in LBE at 250 and 350ºC
  after 3600 h
• Thin oxide layer of Fe3/Cr3 protected
  corrosion at 350 ºC

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• Tensile test in air at 25ºC

Stress-strain curve of 304L in air at 25ºC

• Lowering of ductility on exposure to LBE
• Ductility increased with temperature of LBE
• Increase in UTS after exposure

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• Fractography

Fractography of SS304L, (A) annealed, exposed to
LBE (B) 250ºC (C) 350ºC

• All specimens exhibited ductile fracture.
• Decohesion at second phase particles/inclusion
  s occurred
• to a large extent in case of exposed 304L

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• Microstructure of SS304L

Microstructure of SS304L after oxalic acid etch
(A) annealed, (B) 250ºC and (C) 350ºC
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• EDAX analysis of cross-section

350 ºC
250 ºC
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• SS304L did not undergo any corrosion in LBE
• at 250 and 350ºC after 3600 h.
• No penetration of LBE was seen at either
• temperature

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Thank you