Emergency heat exchanger for cooling the primary fluid of a nuclear reactor, and a process for assembling this heat exchanger

In a liquid metal cooled pool type nuclear reactor having a vessel filled with liquid metal, a reactor core disposed in said vessel, a slab sealing said vessel, an emergency heat/exchanger comprising a support flange resting on the slab, a bundle of exchange tubes bent into a hairpin shape and fixed to two tube plates, a cylindrical shell with a vertical axis surrounding the bundle which is submerged in the liquid metal and a circuit for feeding the tubes of the bundle with a heat exchange fluid, incorporating a means of cooling the exchange fluid heated by the liquid metal and arranged outside the vessel, the two tube plates being placed coaxially, horizontally and at the same level, one of these tube plates, of annular shape, situated peripherally relative to the second, central plate, circular in shape, being fixed to a shell having a vertical axis and ensuring the latter to be borne by the support flange and to a second shell coaxial with the first, situated below the tube plates, and connected to a third shell connected to the central tube plate,

• the improvement wherein the first shell is located above the tube plate, the second and third shells are connected by a connecting piece at their lower ends, and wherein each of the tubes of the bundle incorporates a vertical straight part connected to the central tube plate, a bent plate for returning the tube, a vertical straight return part, said parts being heat-exchanging parts of the tube, as well as a horizontal circular portion extending over approximately one-third of the circumference, and a vertical part joining the peripheral tube plate.