Molten lead (Pb) and its alloys (PbBi and PbLi) are of
immense interest for various nuclear engineering applications,
including but not limited to advanced Lead-cooled Fast Reactors
(LFRs), tritium Breeding Blankets (BBs) of fusion power plants and
spallation targets for Accelerator-Driven Systems (ADS). Owing to
their attractive thermophysical properties, these advanced fluids
assert their candidacy to address the critical requirements of
neutron multiplication, neutron moderation, high temperature
coolants and tritium breeders, enabling the operation of next
generation nuclear systems at high temperatures with better
efficiencies. However, for numerous reasons such as a compromise of
structural integrity at the heat transfer interface, presence of an
inert cover gas during charging of molten metal in the loop, and the
fusion fuel cycle itself may lead to molten metal-gas two-phase
flows with high density ratios. At present, no effective diagnostics
exist to detect such operational and accidental occurrences in high
temperature molten metal systems resulting in a severe lack of
relevant experimental studies. To address these limitations and to
advance the current understanding toward two-phase regimes in high
temperature Pb-based melts, the present work focuses on the design
and assembly aspects of an electrical conductivity-based two-phase
detection sensor array, utilizing high purity
α-Al2O4 coatings with AlPO4 binder as
electrical insulation layers. This paper discusses the design
considerations, thermal analysis, systematic selection of
structural/functional components along with preliminary results from
the probe performance tests in very high temperature
(600°C) static molten Pb column for real time detection of
argon gas bubbles rising within the melt. Quantitative estimations
of time-averaged void fraction, average bubble impaction frequency
and average bubble residence time are presented from the preliminary
experimental investigations.