Investigation of the Dual-Cooled Annular Fuel Effect on the Thermal Power Uprate in a VVER-1000 Nuclear Reactor

Dual-cooled annular nuclear fuel, which is an internally and externally cooled annular fuel, has many advantages for heat transfer. One of the most prominent of these advantages is the ability to harvest more of this type of fuel, which can increase the thermal power of nuclear plants. In this technical note, the core of a VVER-1000 reactor is designed based on the use of internally and externally cooled annular fuels. The thermal-hydraulic parameters of the fuel rods in this type of reactor are analyzed. In addition, the uprate of the thermal power in a VVER-1000 reactor using annular fuels is investigated. For this purpose, first, the proper pitch length of fuel rods in the core is designed under clean and cold conditions using cell and core neutronics calculation codes. Then, thermal-hydraulic calculations are performed for a simulated fuel rod in a hot channel using computational fluid dynamics simulation codes. These calculations are compared with a conventional VVER-1000 reactor that does not use this kind of fuel. One of the most important results of the analysis is that annular fuel shows a sufficient margin for the departure from nucleate boiling and fuel pellet temperature relative to cylindrical fuel. The margin seems viable in accommodating a 129% power uprate.