A. Gessi

Report
Pb and LBE: a technological comparison
Alessandro Gessi, Mariano Tarantino, Pietro Agostini
ENEA Cr Brasimone
40032 Camugnano, BO, Italy
Matgen IV School, Santa Teresa, 21/9/2011
Introduction
• The goal of this work is to compare critically LBE (Lead-Bismuth
Eutectic) and Pb, as coolants for GenIV fast reactors.
• The choice of Heavy Liquid Metals for a nuclear fast reactors, comes
from several known advantages, both technological and nuclear.
• Hystorically, LBE was the first choice, due to its very low melting
point (125°) compared with Pb (327°C).
• However, several esperimental evidences, gained in recent years,
suggest the need of a deep analysis and comparison between LBE
and Pb as coolants, expecially as far as technological issues are
concerned.
• This work is a comparison of the two, starting from basic properties
and going through non metallic elements behaviours, (i.e. Oxygen),
corrosion, of structural materials and related technologies.
Part 1: thermophysical properties (rif. OECD –NEA HLM
Handbook, Chapter 2, A.Gessi, V. Sobolev)
1850
495
Surface tension, (mN m
-1)
.
Pb
445
LBE
Miller, 1954
Semenchenko, 1961
Pokrovsky, 1969
Kazakova, 1984
Novacovic, 2002
Pastor Torres, 2003
Kirillov, 2008
Plevachuk, 2008
Recommended
420
395
370
Bi
1800
Sound velocity (m s -1)
470
Miller, 1951
1750
1700
1650
Bi
345
1600
320
1550
300
500
700
900
1100
1300
300
Temperature, (K)
Dynamic viscosity (10-3 Pa·s)
4.0
Miller, 1954
Kutateladze 1958
3.5
Bonilla, 1964
Pb
Holman, 1968
Kaplun, 1979
2.5
Plevachuck, 2008
Kirillov, 2008
2.0
Recommended
1.5
Bi
1.0
0.5
300
500
700
500
700
Temperature (K)
LBE
3.0
Pb
Pb-Bi(e)
900
Temperature (K)
1100
Stremousov, 1975
Kazys, 2002
Habayashi, 2005
Pb recommended
Bi recommended
Vegard's law
Pb-Bi(e) recommended
1300
900
1100
Part 1: thermophysical properties (rif. OECD –NEA HLM
Handbook, Chapter 2, A.Gessi, V. Sobolev)
18
Bi
Pb
14
Pb-Bi(e)
10
Brown, 1923
Lyon, 1954
Mikryukov, 1956
Powell, 1958
Kutateladze, 1958
Nikol'skii, 1959
Imbeni, 1999
Kirillov, 2008
Plevachuk, 2008
WFL law
Enthalpy increment (J kg-1)
Thermal conductivity (W m -1 K -1)
200
150
100
Recommended
6
300
400
500
600
700
800
900
1000
1100
Pb
Bi
LBE
1200
50
0
300
500
700
900
1100
1300
1500
1700
1900
2100
Temperature (K)
Temperature (K)
Bulk modulus Pb
Bulk modulus Bi
Compressibility LBE
Compressibility Pb
Compressibility Bi
35
150
0.10
0.08
25
0.06
15
0.04
Volumetric CTE (10-6 K-1)
Bulk modulus LBE
Compressibility (GPa-1)
Bulk modulus (GPa)
45
LBE
Bi
Pb
140
130
120
110
100
5
300
500
700
900
0.02
1100 1300 1500 1700 1900 2100
Temperature (K)
300
500
700
900
Temperature (K)
1100
1300
1500
Part 1: thermophysical properties (rif. OECD –NEA HLM
Handbook, Chapter 2, A.Gessi, V. Sobolev)
Volume change at melting and solidification:
A detailed knowledge of volume changes in metals and alloys at their melting points is of critical
importance in the understanding of solidification processes.
• Solid lead. Similar to the majority of metals with the FCC crystal structure, lead exhibits a
volume increase upon melting. At normal conditions a volume increase of 3.81 % has been
observed in pure lead [Iida, 1988].
• The situation is more complicated for LBE freezing and melting accompanied by rapid
temperature change. In the handbook of Lyon [Lyon, 1954] a 1.43 vol. % contraction of LBE on
freezing with a subsequent expansion of the solid of 0.77 vol.% at an arbitrary temperature of
65°C has been reported. P. Agostini et al. [P. Agostini, 2004] and Zucchini et al. [Zucchini,
2005] showed that the consequences of LBE volume expansion by recrystallization could lead
to severe damages to pipeworks. The numerical and experimental studies described show
that over-stressing due to LBE recrystallization and expansion in containment vessels such as
in the MEGAPIE target must be considered during the design phase of the containment
structures and can be managed by means of engineering rules. To avoid over-stressing of
structures it is proposed to redouce:
• the height of each solid LBE layer,
• the presence of internal structures,
• the LBE yield strength.
Part 2: Oxygen
The solubility and diffusivity of Oxygen in Molten Pb and LBE are very similar. The goal
of controlling and monitoring Oxygen is a common need.
Solubility and diffusivity of Oxygen in LBE and Pb, cfr. T. Gnanasekaran, Liquid Metals
and Structural Chemistry Division Chemistry Group, IGCAR
Part 2: Oxygen sensors
Sensor output
Basic components
 Solid electrolyte

Yttria stabilized zirconia (YSZ)

Tubes with 4.5–4.8 mole% Y2O3

"Thimble" with 3 mole% Y2O3
 Reference electrode

Metal/metal-oxide like Bi/Bi2O3 and
In/In2O3 with Mo wire as electric lead

Pt/air using steel wire with platinised tip
as electric lead
 Second (working) electrode

The liquid Pb alloy

Auxiliary wire or the steel housing of
the sensor serves as part of the
electric lead
 Voltmeter reading, E

Measure of the chemical potential of
oxygen in the liquid metal

May in general depend on the specific
combination of the sensor with a highimpedance voltmeter
 Ideal sensor/voltmeter system

Ideal zero-current potential:
 Calculated oxygen concentration, cO:

C1 and C2 are constants specific for the
reference electrode
Oxygen sensors for LBE and Pb are based on the same principles:
galvanic cells using YZR as solid electrolyte. Recent experiments
have shown commonalities between LBE and Pb behaviours
Part 2: Oxygen sensors
Part 2: Oxygen sensors
Configuration of the working electrode
 Metallic sheath (austenitic steel) with Pt mesh

Electric contact by pressing the
electrolyte against the Pt mesh

The contact with the mesh is
established at the highest testing
temperature

Disadvantages are the different thermal
expansion
of YSZ tube and steel sheath
(rupture of the mesh
during cooling) and
oxidation of the steel sheath
at high
temperature
 Pt wire fixed with Pt paste

Allows for producing different thermoelectric
voltages using different materials (wires) for
connecting the Pt wire at the closed end of
electrolyte tube with the sensor housing

Electric contact with the electrolyte may
degrade during thermal cycling

Comparatively small area of electric contact
gives rise to high electrolyte resistance
the
Part 2: Oxygen sensors
Part 2: Oxygen sensors
Characteristics
 Electrolyte thimble
 Seal between electrolyte and housing
immersed in the liquid metal
 Glass ceramic sealant developed for
compatibility with YSZ and steel (thermal),
and with liquid Pb alloys (chemical)
 Reference electrodes:
 Bi/Bi2O3
 3-YSZ with optimized mechanical properties
 Prototype for oxygen measurement in a depth
of ~5 m below the surface of a liquid-metal pool
(based on R&D by IPPE)
Part 2: Oxygen sensors
Part 2: Oxygen sensors
Part 2: Oxygen sensors
Part 2: Oxygen sensors
Sensor 1, 6 m
Sensor 2, 2 m
Thermocouples
Sensor 3, 4 m
Part 2: Oxygen sensors
Part 2: Oxygen sensors
 Sensor design scaled-up from experience
in smaller experimental facilities
 Output significantly decreases for
immersion depth > 1 m
 Improvements of signal transmission
required for oxygen measurements in
pool- type reactors
Output of
reference sensor
Immersion depth
L, м
1
2
3
4
5
1
Output of the sensor
under investigation as
a function of the
immersion depth
Т, °С
V, m/s
Еref, mV
aref
Е6
а6
470
470
480
480
480
480
0,25
0,25
0,25
0,25
0,25
0,25
117
119
120
132
140
148
1
1
1
0,8
0,5
0,4
120
113
102
91
83
141
1
0,4
Design and Testing of
Electrochemical Oxygen
Sensors for Service in Liquid
Lead Alloys
Part 2: Oxygen sensors
Two-shell electric of the
reference electrode with
guarding potential
Part 3: solid slags and black dust
The issue of solid impurities, “black dust” and macroscopic slags, has been one of the most important
topics in the frame of HLM activities and experiments.
In fact, during the operation (with LBE) of the CHEOPE III, LECOR and CIRCE facilities at ENEA several
problems (filters and pipes occlusions, loops’ malfunctions, gas piping's blocks) have been
encountered.
Formed impurities have been sampled and analyzed: the presence of a relatively high amount of G and B
phases together with the 40wt% ca. Of Massicot and Litharge (PbO) suggests a complex formation
mechanism. Also, a sampling method problem exist: analytical methods can determine the
composition of the samples, but not quantitatively determine a possible “formation rate”.
The use of adsorption filters in the liquid phase gave good results. The filtered part appeared to be
enriched in PbO, confirming the selectivity of the filters.
A deeper sealing's control coupled with gas inlet filtration minimized the phenomena in LBE.
NO solid impurity has been observed in flowing Pb (CHEOPEIII last campaign), even after 10.000 hours
of operation, nor any operational problem. A fibreglass filter has been used also in Pb, where a small
amount of PbO has been measured. Outgas systems appear clean.
Part 3: solid slags and black dust
“Black dust” SEM image, CHEOPE III
outgas pipe
Solid slags over CIRCE free level
Examples of microscopic “black dust” and macroscopic
slags (1m ca.)
Part 3: solid slags and black dust
Compound
Concentration
PbO
40 wt% ca.
LBE (g b phases)
50 wt% ca.
Fe, Al, Cr
10 wt % Ca.
Table 1 Composition of a slag in the CHEOPE loop, LBE, 400°C, outgas filter.
Compound
Concentration
PbO
60 wt% ca.
LBE (g b phases)
30 wt% ca.
Fe, Al, Cr
10 wt % Ca.
Table 2. Composition of the filtered particles, fiberglass adsorption filter in the liquid phase, LBE, CHEOPE III
Compound
Concentration
PbO
15 wt% ca.
Pb
80 wt% ca.
Fe, Al, Cr
5 wt % Ca.
Table 3. Composition of few filtered particles, fiberglass adsorption filter, liquid phase CHEOPEIII, Pb,
500°C.
Part 3: solid slags and black dust
(* P. Turroni et Al., J.Vac. Sc. Tech. A 22(4)).
Experiments performed in the frame of the
TRASCO program: evaporation rates vs
temperature.
Part 3: solid slags and black dust
The observed mechanism of solid impurities (gas and liquid phase) can be summarized as follows:
Uncontrolled cold area on the facility
Air pollution (ingas pollution)
(2Pb+O2
samples.
2PbO)
LBE recrystallization-phase separation
(In the cold leg of LBE loops, T=350°C)
Particle formation-macroscopic slags
(reducing gas mixture bubbling is not effective)
Loop draining-cooling down
(samples are taken at room temperature in air)
In the CHEOPE III loop Pb operated, where T=500°C and the maximum DT with the cold leg is
80°C, no slags or black dust has been observed.
An indirect confirmation of this speculative mechanism is the recrystallized LBE found in the
filters: it is not Pb+Bi but Gamma and Beta phases (Pb7Bi3 and Bi99,9Pb), suggesting a rapid cold
point freezing.
The formation of “black dust” happens ONLY with LBE.
Part 4: corrosion
The need for data on reference structural materials in contact with HLM is a crucial
issue in the development of GenIV technologies.
Lead and LBE are two highly corrosive media. The possibility to protect them by
means of in situ passivation or artificila protections are widely studied in the
frame of european programmes
Corrosion mechanisms are driven by the same principles, both in LBE and in Pb.
Elemental solubilities can generally be considered similar.
However, given the higher temperatures of a Pb cooled reactor, corrosion
phenomena are generally worse.
Protecting steels from corrosion by means of in situ passivation is quite
straighforward in LBE at 400°C, extremely tricky and less effective in pure Pb, at
500°C. in the latter, corrosion happens by means of mass transfer more than
elemental straight dissolution.
Part 4: corrosion
T91 exposed to LBE, 3.000 hours of experiments, 500°C, Oxygen 10-6wt%. Thick protective oxide scales.
Part 4: corrosion
T91 exposed to Pb, 10.000 hours of experiments, 500°C, Oxygen 10-6wt%. Weak, thick, quickly formed oxide
scales, easily eroded by HLM flux.
FPN FIS ING
Part 4: corrosion
Fe: 89.5 wt%
Cr: 8.3 wt%
Fe: 71.4 wt%
Cr: 8.4 wt%
O: 18.5 wt%
Fe: 41.5 wt%
Cr: 12.5 wt%
O: 42.9 wt%
Fe: 57.0 wt%
Cr: 0.4 wt%
O: 41.3 wt%
20 mm scale micrography: oxide layers with corresponding EDS spots
FPN FIS ING
Part 4: corrosion
10.3 µm
 The coating scale have a very good continuity;
 Oxygen precipitation is observed below the FeAl
coating;
 Small damages are observed in the coating maybe
due to the post examination analysis;
Part 4: corrosion
16 µm
33 µm
Part 4: corrosion
Old experiment at 400°C and
latest experiment at 500°C.
s Is the corrosion depth in
microns
FPN FIS ING
Part 4: corrosion
Corrosion curves for old and new experiments. Few points do not allow a
critical comparison.
FPN FIS ING
Conclusion
•
The choice between LBE and Pb as coolants for GenIV fast reactor is connected
to several open points:
1.
Technological advantages and disadvantages (i.e. melting point, volume
expansion, solid impuririties production, higher temperatures for structural
materials)
2.
Commercial issues, expecially Bi cost and natural abubdance
3.
Nuclear safety issues, expecially Po210 aerosols production by irradiated Bi. The
global amount of Polonium is produced only by Bi. With pure Pb, only the Bi
traces are responsible of the eventual Polonium aerosol.
The protection of structural materials from high temperature corrosion is thus the
critical open point for Pb LFR technologies. Once solved, Pb could be the winning
choice over LBE.

similar documents