  The PandaX-30T is a proposed next-generation experiment to study dark matter
and neutrinos using a dual-phase time projection chamber with \textasciitilde30
tons of liquid xenon. An innovative xenon handling subsystem of the PandaX-30T,
the First-X, is described in this paper. The First-X is developed to handle
liquid xenon safely and efficiently, including liquefying and long-term storing
xenon without losses or contamination, and transferring cryogenic liquid xenon
between the storage module and the detector safely and effectively without
venting out. The storage module of the First-X is five specially designed
double-walled cylindrical vessels (Center Tanks) equipped with three heat
exchangers each for pressure and temperature regulation. Each Center Tank is
designed with a vacuum and multi-layer insulation and a maximum allowable
working pressure of 7.1 MPa, allowing 6 tons of xenon to be stored at 165--178
K at 0.1--0.2 MPa in the liquid phase or up to 300 K and up to 6.95 MPa in the
supercritical phase. High-pressure storage (\textgreater0.2 MPa) only occurs in
case of long-term detector shutdown or lack of nitrogen, ensuring no-loss
storage of 6 tons of xenon in the range 178--300 K. In this paper, the
thermophysical performances of the First-X and innovative scenarios to conduct
non-vented cryogen transportation were experimentally conducted and reported
using liquid argon. The non-vented cryogenic liquid filling and pump-assisted
cryogenic liquid recovery have been conducted with liquid argon at a mass flow
rate of 1390 kg/h, corresponding to a xenon mass flow rate of 2140 kg/h.
Compared with the PandaX-4T, the transportation of xenon between the detector
and the storage module is conducted in the liquid phase rather than in the
gaseous phase, and the filling rate and the recovery rate are increased by
approximately 50 times and 30 times, respectively.
