Cryogenic storage container

In a cryogen storage container for storing a liquid cryogen formed of one of hydrogen, helium, and neon wherein the cryogenic storage container comprises:

• a pressure vessel for containing the liquid cryogen;
• a vacuum vessel having an outer wall surrounding and spaced from the pressure vessel for subjecting the space between the outer wall and the pressure vessel to a vacuum;
• a pair of inlet and vent lines penetrating the vacuum vessel and in communication with the pressure vessel for filling the pressure vessel with the liquid cryogen and for venting boil-off vapor from the liquid cryogen, respectively;
• an intermediate heat shield spaced between the outer wall of the vacuum vessel and the pressure vessel for intercepting heat that would otherwise be transferred from the vacuum vessel to the pressure vessel;
• a set of first and second layers of insulating material located between the intermediate heat shield and the outer wall of the vacuum vessel and the pressure vessel, respectively., and a liquid nitrogen container, formed of a heat conductive material, located in thermal contact with the intermediate heat shield, and containing liquid nitrogen to absorb the heat intercepted by the intermediate heat shield through vaporization of the liquid nitrogen;
• wherein the improvement comprises:
• a sub-intermediate heat shield interposed between the second insulation layer and the pressure vessel for intercepting heat that would otherwise be transferred from the intermediate heat shield to the pressure vessel;
• a third insulation layer located between the sub-intermediate heat shield and the pressure vessel;
• intermediate heat absorption means in thermal contact with the sub-intermediate heat shield and containing a coolant for absorbing the heat intercepted by the sub-intermediate heat shield by undergoing a phase change, the coolant having a phase transition temperature, at which the phase change occurs, below the boiling temperature of liquid nitrogen;
• and
• recovery means connected to the intermediate heat absorption means for recovering the coolant after having undergone the phase change for regeneration of the coolant.