A method for the long-term storage of spent nuclear fuel consisting in the steps of: - discharging a removable unit as a whole from the reactor, wherein the removable unit comprises spent nuclear fuel, wherein the spent nuclear fuel constitutes an active zone, and wherein discharching of the removable unit occurs without disassembling the active zone, and - placing it inside a cooldown and storage tank preliminarily placed in a mine with a cooling system and filled with an eutectic liquid lead-bismuth alloy, wherein the construction of the cooldown and storage tank, is characterized in that submerging the spent nuclear fuel being part of the removable unit therein below the level of the eutectic lead-bismuth alloy provides natural circulation conditions, - maintaining a liquid state of the eutectic lead-bismuth alloy and - monitoring a temperature thereof to remove afterheat of the spent nuclear fuel being part of the removable unit through a housing of the cooldown and storage tank to the mine without exceeding the permissible temperature of the eutectic lead-bismuth alloy during a storage period until afterheat of the spent nuclear fuel being part of removable unit is reduced to the required level, - after that the cooldown and storage tank is removed from the mine and put within an on-site cask without exceeding the permissible temperature of the eutectic lead-bismuth alloy during the removal of afterheat of the spent nuclear fuel due to the natural circulation of atmospheric air until the eutectic lead-bismuth alloy solidifies therein, then - the cooldown and storage tank is reloaded from the on-site packing container into a cask without taking additional heat removal measures, and is transported to an area for long-term storage or processing of the spent nuclear fuel contained inside it, and afterwards, - discharging the spent nuclear fuel being part of the removable unit, from the cooldown and storage tank into a long-term storage tank on a special site or - disassembling the active zone being part of the removable unit at an enterprise for processing a spent nuclear fuel, for which the eutectic lead-bismuth alloy is preliminary brought to a liquid state by means of a heating system. - discharging a removable unit as a whole from the reactor, wherein the removable unit comprises spent nuclear fuel, wherein the spent nuclear fuel constitutes an active zone, and wherein discharching of the removable unit occurs without disassembling the active zone, and - placing it inside a cooldown and storage tank preliminarily placed in a mine with a cooling system and filled with an eutectic liquid lead-bismuth alloy, wherein the construction of the cooldown and storage tank, is characterized in that submerging the spent nuclear fuel being part of the removable unit therein below the level of the eutectic lead-bismuth alloy provides natural circulation conditions, - maintaining a liquid state of the eutectic lead-bismuth alloy and - monitoring a temperature thereof to remove afterheat of the spent nuclear fuel being part of the removable unit through a housing of the cooldown and storage tank to the mine without exceeding the permissible temperature of the eutectic lead-bismuth alloy during a storage period until afterheat of the spent nuclear fuel being part of removable unit is reduced to the required level, - after that the cooldown and storage tank is removed from the mine and put within an on-site cask without exceeding the permissible temperature of the eutectic lead-bismuth alloy during the removal of afterheat of the spent nuclear fuel due to the natural circulation of atmospheric air until the eutectic lead-bismuth alloy solidifies therein, then - the cooldown and storage tank is reloaded from the on-site packing container into a cask without taking additional heat removal measures, and is transported to an area for long-term storage or processing of the spent nuclear fuel contained inside it, and afterwards, - discharging the spent nuclear fuel being part of the removable unit, from the cooldown and storage tank into a long-term storage tank on a special site or - disassembling the active zone being part of the removable unit at an enterprise for processing a spent nuclear fuel, for which the eutectic lead-bismuth alloy is preliminary brought to a liquid state by means of a heating system.