Measurement of the radon concentration in the ultrapure water of the JUNO-LS UPW system

Abstract The Jiangmen Underground Neutrino Observatory (JUNO) is an under-construction multi-purpose neutrino experiment primarily aiming to determine the neutrino mass ordering and precisely measure the neutrino oscillation parameters. The JUNO detector consists of a Central Detector (CD), a Water Cherenkov Detector (WCD), and a Top Tracker (TT). The target volume of JUNO is 20-kton ultrapure Liquid Scintillator (LS) purified by a system combining alumina oxide filter, distillation, LS mixing, water extraction, and gas stripping. Notably, the water extraction system necessitates a substantial volume of ultrapure water to eliminate radioactive metal ions from LS by fully mixing in the extraction tower. Since the radon gas is much easier to dissolve in LS than in water, the radon concentration in the ultrapure water must be strictly controlled. An ultrapure water system has been developed for the water extraction system. The radon is removed from water by degassing membranes, and the radon concentration in water is measured online by a highly sensitive radon measurement system. This paper will present the ultrapure water system, the radon measurement system, and current radon concentration results at different process sections of pure water system.