Techno–economic comparison of power conversion units for the next generation nuclear plant
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The choice of thermodynamic cycle configuration is a vital first step in the development of a new nuclear power plant. Various cycle configurations for High Temperature Gas Reactor power conversion are under investigation. The choice of optimum cycle configuration is a complex problem influenced by a large number of interdependent parameters such as component and material limitations, maintenance, risk and cost. Because identifying the optimum PCU is such a complex and integrated problem it is often difficult to assess the comparative cost and feasibility of each cycle during the concept phase. This forces developers to mainly consider performance and practical considerations when justifying the choice of cycle configuration. Unfortunately, the effect of many of these interdependent parameters on the plant cost can be overlooked when only the cycle performance and practicality are evaluated. An integrated approach is needed in order to highlight the underlying parameters that will impact on the feasibility of a particular cycle. There is therefore a need for an integrated decision-support tool that can systematically compare various cycle configurations and evaluate the efficiency and cost as a function of various design parameters. The objective of this study was to compare the most promising one-, two- and three-shaft Brayton-, Rankine- and Combined-cycle configurations in order to evaluate the technical performance, practical considerations and economical competitiveness when employed in conjunction with a given Pebble Bed Reactor. The objective was to identify a near-optimum design for each cycle configuration from which the optimum Power Conversion Unit (PCU) configuration for the Next Generation Nuclear Plant could then be identified. The order-of-magnitude plant cost was the main parameter used to compare the various cycle configurations. The following methodology was used in the investigation in order to arrive at the order-of-magnitude plant cost and ultimately at the optimum PCU configuration: Ten promising cycle configurations were identified. A thermodynamic cycle analysis was done for each configuration. Component models were developed for the turbine, compressor, heat exchanger and blower. These component models were used together with the boundary values from the cycle analyses to perform a conceptual design of each component. The results from each component model were used to translate the component's geometry into cost, using postulated costing models for each component. The power output for each cycle was translated into a capitalised income resulting in a reduction in capital cost. The temperatures, pressures, efficiency, component capital costs and the order-of-magnitude plant cost of each configuration were then calculated for various pressure ratios, reactor outlet temperatures and power turbine speeds. Based on these results, the different operational parameter envelopes were identified for which each of the different cycle configurations would be most appropriate. The performance, practical considerations and economical competitiveness of each of the ten selected cycles were evaluated. The single-shaft inter-cooled recuperative direct Brayton cycle (Cycle B) is recommended only when the reactor outlet temperature is lower than 900 °C and the reactor power is lower than 400 MW. Altertatively, at higher reactor outlet temperaures and at higher power levels the single-shaft recuperative direct Combined Cycle without inter-cooling (Cycle J) is recommended. The results from this study suggest that the single-shaft recuperative direct Combined Cycle without intercooling (Cycle J) is the most appropriate PCU for the PBMR for the Next Generation Nuclear Plant.
- Engineering