Vapor pressure measurement of heavy liquid metal
samples by transportation method: first observations
at SCK·CEN
Borja Gonzalez1,2 and Alexander Aerts1
1: Advanced Nuclear Systems-Nuclear Systems Research/ Conditioning and Chemistry Programme, Belgian Nuclear Research Centre, SCK•CEN, Mol, Belgium
2: Centre for Surface Chemistry and Catalysis, Bioscience Engineering Faculty, Katholieke Universiteit Leuven, KUL, Leuven, Belgium
Abstract
During operation of reactors cooled by lead-bismuth eutectic (LBE), significant amounts of Po-210 are formed. Knowledge of Po-210 volatilization from LBE is essential to ensure safe
operation of such reactors. Transportation method has been successfully used to determine equilibrium vapor pressures of Po solutions in LBE by several researchers. The performance
of a transportation set-up at SCK·CEN has been evaluated at first instance by evaporating pure Bi samples. During these first experiments, large amounts of aerosols were generated being
a potential source of contamination. Characterization of these aerosols showed micron-size Bi particles. The insertion of a copper foil made the decrease of temperature less severe at the
exit of the oven, resulting in disappearance of aerosols. Evaporation experiments were also performed at different temperatures. The typical vapor pressure dependence with temperature
was found and the results were compared with literature data. Furthermore, evaporation experiments with Po-doped LBE were performed. Preliminary studies, concerning the detection
efficiency of Po-210 and the homogeneity of Po-doped LBE samples were done. Moreover, the release of Po from the doped LBE sample in function of temperature was analyzed and
compared with Neuhausen. Henry constant was also calculated and a correlation with temperature was derived and compared with literature data.
Transportation method
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Results of bismuth evaporation
Controlled flow of carrier gas (Ar/5%H2) over liquid metal sample
Accurate knowledge of temperature needed
Sample heated to constant temperature
Emanating vapors transported away by the carrier gas and then
condense in colder zones of the setup.
Filter systems for safety and contamination monitoring.
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Paper filter at the exhaust
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Activated carbon at the exit of the oven
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Silicon oil bottle
Characterization of bismuth aerosols
• Bismuth metal particles
• Uniform internal structure and smooth surface
• Size in the order of micrometers
Uniform internal
structure
Smooth surface
Bi metal
particles
0,1 nm
1 nm
10 nm
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Weight loss to detemine vapor pressue
Consider Bi (g) and Bi2 (g)
Typical vapor pressure-temperature dependence
Monodisperse ~1
µm particles
SAXS
WAXS
Bismuth evaporation
DLS
100 nm
1 µm
Results of polonium evaporation
Influence of LBE concentration on Po-210 detection efficiency
by Liquid Scintillation Counting (LSC)
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Measurement of evaporated Po by using LSC
Solutions with different LBE concentration
Below 1 g/L PbBi: quantitative determination of alpha emitters
Above 1 g/L PbBi: decrease of total number of counts  decrease
efficiency
Homogeneity of distribution of Po-210 in Po-doped LBE
samples
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No particular segregation was observed
Uniform distribution of Po along the sample
Po evaporation
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Evaporation of dissolved component (Po in LBE)
Evaporation experiments at different temperatures
Typical release curve versus temperature
Shifted to higher temperatures due to higher sample mass
Henry constant calculation
Derivation of correlation with temperature
Conclusions and future work
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First Po evaporation experiments with results in agreement with literature data
Developed procedures to determine Po content of LBE by LSC
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Working in saturated conditions? Evaporation experiments with variation of gas flow rate
Evaporation experiments with higher Po concentrations and different gas composition
Analysis of activated carbon as a first step towards the development of filter systems
www.sckcen.be
[email protected]
201214_BGonzalez