Distillation and stripping pilot plants for the JUNO neutrino detector: Design, operations and reliability

Abstract

This paper describes the design, construction principles and operations of the distillation and stripping pilot plants tested at the Daya Bay Neutrino Laboratory, with the perspective to adapt these processes, system cleanliness and leak-tightness standards to the final full scale plants to be used for the purification of the liquid scintillator of the JUNO neutrino detector. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Purification of liquid scintillator will be performed with a system combining alumina oxide, distillation, water extraction and steam (or N 2 gas) stripping. Such a combined system will aim at obtaining a total attenuation length greater than 20 m @430 nm, and a bulk radiopurity for 238 U and 232 Th in the 10 -15 ÷10 -17 g/g range. The pilot plants commissioning and operation have also provided valuable information on the degree of reliability of their main components, which will be particularly useful for the design of the final full scale purification equipment for the JUNO liquid scintillator. This paper describes two of the five pilot plants since the Alumina Column, Fluor mixing and the Water Extraction plants are being developed by the Chinese part of the collaboration.

A complete optical model for liquid-scintillator detectors

“…We expect this model to be valuable for designing future LS-based detectors, as well as improving the agreement between the Monte Carlo simulation and the experimental data in currently on-going experiments. For example, in order to verify the design of LS purification system of the JUNO experiment, a LS pilot plant was built at the Daya Bay experimental site [33], and the 20-ton Gadolinium-doped LS in one anti-neutrino detector of Daya Bay was replaced with the purified LS without Gd. During the LS replacement, different sets of PPO and bis-MSB concentrations were tested in a step-wise way, and for each LS recipe the light yield was measured with 60 Co source.…”

Novel opaque scintillator for neutrino detection

“…The radiopurity of LAB and PPO is already known from others projects. The LAB-based LS in Daya Bay achieved radiopurities for uranium (U) and thorium (Th) of < 10 −12 g/g and JUNO is expecting to achieve concentrations in the 10 −15 -10 −17 g/g range [8]. The radiopurity of liquid n-paraffins with shorter chains was also demonstrated [2,9].…”

Optimization of the JUNO liquid scintillator composition using a Daya Bay antineutrino detector

“…Details of the distillation and steam stripping systems have been reported in Ref. [23]. The attenuation length of the purified LAB was measured to be 25.1 m at the photon wavelength of 430 nm, and the attenuation length of the initial LS was 23.8 m. The uncertainties of these values were about 2 m, primarily from the relatively short light path compared to the attenuation length.…”