Patent Number: 
Section: claims

1. A riser for defining a coolant flow path in a nuclear reactor including a hot leg flowing inside the riser and a cold leg flowing outside the riser, the riser comprising:a hollow cylindrical upper riser section having a smaller diameter;a hollow cylindrical lower riser section having a larger diameter that is larger than the smaller diameter of the hollow cylindrical upper riser section; anda riser cone compressed between a lower end of the hollow cylindrical upper riser section and an upper end of the hollow cylindrical lower riser section, the riser cone including a frustoconical body having a lower end mating with the upper end of the hollow cylindrical lower riser section, a sealing ring including an upper end mating with the lower end of the hollow cylindrical upper riser section, and a spring compressed between the sealing ring and an upper end of the frustoconical body so that the riser cone provides sealing between the lower end of the hollow cylindrical upper riser section and the upper end of the hollow cylindrical lower riser section. 2. The riser of claim 1 wherein the hollow cylindrical lower riser section comprises a core basket or shroud surrounding a nuclear reactor core. 3. The riser of claim 2 wherein the hollow cylindrical lower riser section further comprises a riser transition weldment disposed on the core basket or shroud, the riser transition weldment including interface features engaging the lower end of the riser cone. 4. The riser of claim 1 wherein the riser cone comprises a frustoconical compression sealing ring accommodating the difference between the smaller diameter of the hollow cylindrical upper riser section and the larger diameter of the hollow cylindrical lower riser section. 5. The riser of claim 1 wherein the spring comprises a nested wave spring.