Patent Number: 040615340
Section: claims

1. A nuclear reactor comprising a concrete shielding vessel with a steel lining, containing a freezable liquid metal coolant comprising the element sodium, a solid nuclear reactor core, a primary heat exchanger and a pump means all submerged in the coolant, the pump means being provided for circulating the coolant liquid within the vessel, cooling pipes within the vessel adjacent the inner surface of said vessel for effecting the freezing of the liquid coolant at the inner surface of the vessel, said cooling pipes containing a liquid metal cooling fluid, an interior wall adjacent the said inner surface, said interior wall comprising a frozen layer of the liquid coolant on and supported by the cooling pipes and the inner surface of the vessel, the said frozen layer interior wall being thin relative to the overall cross-section of the vessel. 2. A nuclear reactor according to claim 1, in which the pipes extending over the surface are closed loops, each loop including a cooler externally of the concrete and steel vessel, and a forced air cooling system for cooling the said liquid metal coolant in the closed loops at the cooler. 3. A nuclear reactor according to claim 1, including additional cooling pipes embedded in the concrete in proximity to the lining. 4. A nuclear reactor according to claim 3, including thermal insulation spaced from said surface. 5. A nuclear reactor according to claim 4, wherein said thermal insulation is located with runs of said cooling pipes disposed on both sides thereof. 6. A nuclear reactor according to claim 1, wherein the liquid coolant is sodium and the cooling fluid within the closed loops contains sodium-potassium alloy, and including further pipes embedded in the concrete and means for passing forced air therethrough. 7. A nuclear reactor according to claim 1, said interior wall being of sufficient thickness such that when the temperature of the liquid coolant inside is 400.degree. C, the temperature at the outer surface of the interior wall is approximately 50.degree. C.