Liquid metal cooled nuclear reactor comprising a passive decay heat removal system having thermal insulation attached to a wall of a cold source reservoir that holds a phase change material, where the insulation is arranged to automatically fall by gravity from the wall in response to the wall reaching a predetermined temperature

A fast neutron nuclear reactor cooled by liquid metal, comprising:

• a primary containment vessel filled with a liquid metal as a heat-exchange fluid of the primary circuit of the reactor;
• a containment vessel sink located around the primary containment vessel and defining an inter-vessel space between the primary containment vessel and the containment vessel sink;
• a closer slab to enclose the liquid metal inside the primary containment vessel;
• a system for evacuation of both
• at least some heat of the reactor during normal operation, and
• decay heat of the reactor during an accident situation, the system including:
• a closed circuit filled with a heat-exchange liquid, the closed circuit including:
• a layer of a plurality of U-shape pipes located in the inter-vessel space and distributed around the primary containment vessel, each of the pipes extending along the primary containment vessel with a bottom of the U-shapes adjacent to a bottom of the primary containment vessel,
• the closed circuit being configured so that the heat-exchange liquid circulates therein by natural convection, and
• remains in the liquid state both
• during normal operation of the reactor, and
• during an accident situation releasing decay heat;
• a cold collector,
• the cold collector being connected to a cold branch of the U of each of the pipes, and
• the cold collector being arranged outside and above the closer slab,
• a hot collector,
• the hot collector being connected to a hot branch of the U of each of the pipes, and
• the hot collector being arranged outside and above the closer slab,
• at least one heat exchanger having one end connected to the cold collector and the other end connected to the hot collector,
• a cold source including:
• at least one reservoir located at a distance from the primary containment vessel and above the closer slab, the reservoir comprising an external wall, the reservoir containing the heat exchanger therein, the reservoir containing a phase change material capable of being in a solid state and in a liquid state, the phase change material being configured, during the exchange with the heat exchanger, to be in the solid state during normal operation of the nuclear reactor and to transition to the liquid state during an accident situation of the reactor in which decay heat is released;
• a thermal insulating layer;
• the thermal insulating layer being attached to the external wall of the reservoir via at least one attachment element, and
• the at least one attachment element being configured to cause the thermal insulating layer to be automatically detached from the wall in response to the wall reaching a predetermined temperature, which allows the thermal insulating layer to fall by gravity from the external wall of the reservoir.