A gas siphon type reactor (10) is used to carry out a three phase chemical
reaction under pressure, such as the reduction of uranyl nitrate to
uranous nitrate by hydrogen, in the presence of a catalyst made up of
platinum on a silica carrier. The control of the pressure in the reactor
(10) is provided by regulating the liquid and gas flow rates from a high
pressure separator (52), into which the liquid and the gas leaving the
reactor (10) are routed. The liquid in the reactor (10) is tapped from a
lateral branch pipe (32) fitted with a filter (36) and emerging in the
upper area (30), behind a profiled wall (34).
