Development of thermodynamic cycles for sodium-cooled-fast reactors.

Abstract

Currently, one engineering challenge is designing Generation IV (GEN-IV) Nuclear Power Plants (NPPs) with significantly higher thermal efficiencies compared to current NPPs, and to match, or at least to be close to, the thermal efficiencies reached by fossil-fired power plants, which are currently at the level of 40-62%. As there are six GEN-IV nuclear-reactor concepts and the performance of these reactors-concepts depends on their design, it is reasonable to start with all GEN-IV reactor concepts and investigate the coolants and their characteristics in these concepts. For this objective, main thermophysical, corrosion, and neutronic properties of coolants of the GEN-IV reactors within the proposed temperature range of operation were investigated. Heat Transfer Coefficients (HTCs) for the coolants of the GEN-IV concepts were also calculated and compared to typical HTCs published in the open literature for coolant candidates. Based on a comparison of properties and HTCs, a Sodium-cooled Fast Reactor (SFR) - one of the six concepts considered under the Generation IV International Forum (GIF), was selected because it is the most experienced reactor technology among all of the proposed GEN-IV reactor concepts. Moreover, with depleting uranium resources, there is an interest to design reactors that operate on a closed fuel cycle, and SFR is one of the potential options. A BN-600 reactor is a sodium-cooled fast-breeder reactor built at the Beloyarsk NPP in Russia, and it is in operation since 1980. On the secondary side it utilizes a subcritical-pressure Rankine-steam cycle with heat regeneration. The power-conversion system is presented, and calculations of thermal efficiency of this scheme have been performed and analyzed. To achieve higher thermal efficiency of the plant, one of the possibilities is to increase thermal efficiency of the turbine cycle. Two main approaches for the SFR in terms of the power-conversion cycle were investigated: supercritical-pressure Rankine-“steam” cycle and supercritical-pressure CO2 Brayton-gas-turbine cycle. The feasibility of these options is discussed. The thermal efficiencies of ideal and non-ideal CO2 Brayton gas-turbine cycles were optimized by varying CO2 pressures and temperatures at the outlet of Na-CO2 heat exchanger.