With reference to loss-of-coolant accidents in light water reactors, the critical flows of subcooled liquids are examined, particularly from the viewpoint of the time extension of the metastability state. “Ad hoc” tests have outlined an upper limit of this time range at 10−4 s. The flow characteristics of the unbounded jets have been investigated both externally (via photographic measurements of the external shapes at various subcoolings) and internally (via pressure profiles in the radial direction). As far as pressure profiles within the jet are concerned, the presence in the jets characterized by the subcooled inlet conditions of a central liquid core gradually evaporating has been outlined.