Development of a Compact Multivariable Sensor Probe for Two-Phase Detection in High Temperature PbLi–argon Vertical Columns

Abstract: Existence of a two-phase flow in lithium-based Liquid Metal (LM) breeders for nuclear fusion blankets are a cause of concern due to critical issues including reduced tritium breeding ratio (TBR), generation of hot-spots and improper nuclear shielding. Additionally, a large density ratio between LM and gas requires experimental database towards development and validation of numerical models. Lead–lithium (PbLi) has gained immense focus for its various advantages and is utilized in several breeding-blanket concepts. In this view, a LM–gas two-phase detection diagnostics is imperative for PbLi environment. Two-phase detection in high electrical-conductivity fluids like LMs is greatly facilitated by electrical-conductivity probes due to ruggedness, fabrication ease and operational simplicity. However, corrosive nature of PbLi with high operational temperature severely restricts commercial electrical-insulations, a foremost requirement for electrical-conductivity based detection schemes. In this study, an electrical-conductivity and temperature based multivariable two-phase detection probe is developed using high-purity alumina coatings. Probe validation is performed in PbLi–Ar vertical column with LM temperature upto 400°C and time-averaged void-fractions upto 0.95, covering flow-regimes from bubbly flow upto in-box loss of coolant accident (LOCA). Developed probe provides high reliability and temporal resolution towards individual bubble detection through electrical-conductivity principle alongwith simultaneous temperature trends for two-phase mixture. Present paper discusses probe fabrication and calibration, LM–gas two-phase facility, time-averaged void-fraction estimations, bubble frequency and residence time estimations alongwith critical observations from the preliminary tests.