Comparative analysis on high-efficiency energy conversion system with different working mediums matched with small lead-cooled fast reactor

Transient discharge performance of high-temperature latent storage system integrated with supercritical CO2 Brayton cycle: A combined analytical and numerical study

Significant progress has been made in the ongoing development of the Argonne National Laboratory (ANL) Plant Dynamics Code (PDC), the ongoing investigation and development of control strategies, and the analysis of system transient behavior for supercritical carbon dioxide (S-CO{sub 2}) Brayton cycles. Several code modifications have been introduced during FY2011 to extend the range of applicability of the PDC and to improve its calculational stability and speed. A new and innovative approach was developed to couple the Plant Dynamics Code for S-CO{sub 2} cycle calculations with SAS4A/SASSYS-1 Liquid Metal Reactor Code System calculations for the transient system level behavior on the reactor side of a Sodium-Cooled Fast Reactor (SFR) or Lead-Cooled Fast Reactor (LFR). The new code system allows use of the full capabilities of both codes such that whole-plant transients can now be simulated without additional user interaction. Several other code modifications, including the introduction of compressor surge control, a new approach for determining the solution time step for efficient computational speed, an updated treatment of S-CO{sub 2} cycle flow mergers and splits, a modified enthalpy equation to improve the treatment of negative flow, and a revised solution of the reactor heat exchanger (RHX) equations coupling the S-CO{sub 2} cycle to the reactor, were introduced to the PDC in FY2011. All of these modifications have improved the code computational stability and computational speed, while not significantly affecting the results of transient calculations. The improved PDC was used to continue the investigation of S-CO{sub 2} cycle control and transient behavior. The coupled PDC-SAS4A/SASSYS-1 code capability was used to study the dynamic characteristics of a S-CO{sub 2} cycle coupled to a SFR plant. Cycle control was investigated in terms of the ability of the cycle to respond to a linear reduction in the electrical grid demand from 100% to 0% at a rate of 5%/minute. It was determined that utilization of turbine throttling control below 50% load improves the cycle efficiency significantly. Consequently, the cycle control strategy has been updated to include turbine throttle valve control. The new control strategy still relies on inventory control in the 50%-90% load range and turbine bypass for fine and fast generator output adjustments, but it now also includes turbine throttling control in the 0%-50% load range. In an attempt to investigate the feasibility of using the S-CO{sub 2} cycle for normal decay heat removal from the reactor, the cycle control study was extended beyond the investigation of normal load following. It was shown that such operation is possible with the extension of the inventory and the turbine throttling controls. However, the cycle operation in this range is calculated to be so inefficient that energy would need to be supplied from the electrical grid assuming that the generator could be capable of being operated in a motoring mode with an input electrical energy from the grid having a magnitude of about 20% of the nominal plant output electrical power level in order to maintain circulation of the CO{sub 2} in the cycle. The work on investigation of cycle operation at low power level will be continued in the future. In addition to the cycle control study, the coupled PDC-SAS4A/SASSYS-1 code system was also used to simulate thermal transients in the sodium-to-CO{sub 2} heat exchanger. Several possible conditions with the potential to introduce significant changes to the heat exchanger temperatures were identified and simulated. The conditions range from reactor scram and primary sodium pump failure or intermediate sodium pump failure on the reactor side to pipe breaks and valve malfunctions on the S-CO{sub 2} side. It was found that the maximum possible rate of the heat exchanger wall temperature change for the particular heat exchanger design assumed is limited to {+-}7 C/s for less than 10 seconds. Modeling in the Plant Dynamics Code has been compared with available data from the Sandia National Laboratories (SNL) small-scale S-CO{sub 2} Brayton cycle demonstration that is being assembled in a phased approach currently at Barber-Nichols Inc. and at SNL in the future. The available data was obtained with an earlier configuration of the S-CO{sub 2} loop involving only a single-turbo-alternator-compressor (TAC) instead of two TACs, a single low temperature recuperator (LTR) instead of both a LTR and a high temperature recuperator (HTR), and fewer than the later to be installed full set of electric heaters. Due to the absence of the full heating capability as well as the lack of a high temperature recuperator providing additional recuperation, the temperature conditions obtained with the loop are too low for the loop conditions to be prototypical of the S-CO{sub 2} cycle.

This paper first presents a new powertrain based on a two-battery High-Efficiency Energy Conversion System (HEECS) chopper that is suitable for electric vehicles (EVs). The HEECS chopper is based on the principle of a partial power conversion circuit, and the overall efficiency is over 99% in a wide load range. The efficiency of this powertrain was measured in the steady state by two types of powertrains, a non-chopper powertrain and an HEECS chopper-based powertrain, using a motor test bench. On the basis of these data, several driving tests, such as the Worldwide-harmonized Light vehicles Test Cycle (WLTC), were simulated, and four driving cycle patterns were included. A 6.4% reduction in energy consumption was observed in WLTC low mode compared with the energy consumed by the non-chopper powertrain in the experiments. Thus, the HEECS chopper-based powertrain is more suitable for low-speed driving ranges than high-speed ranges.

This paper proposes a State of Charge (SOC) balancing control combined with flux-weakening for two-battery high-efficiency energy conversion system (HEECS) chopper-based powertrain. The HEECS chopper has an advantage of very high DC-DC power conversion efficiency using two batteries. This HEECS chopper based EV power train can realize longer driving range by changing the DC bus voltage depending on the EV speed [1]. However, SOCs of batteries can be imbalance because the driving pattern is not predictable. This paper proposes an effective method for balancing SOCs by modifying HEECS chopper’s control according to the driving speed. Simulation results show the proposed method extends driving range by 2.8% compared with the conventional SOC balancing method. The SOC difference is very small when the one of SOCs become zero.

Investigation on the thermodynamic performance and machinery mass in the N2O-based mixtures recompression Brayton cycle for a nuclear-powered spacecraft

• Developed dynamic models to simulate LFR-based nuclear propulsion systems. • Introduced the Ship-to-Shore concept, enabling clean energy transfer to ports. • Achieved significant CO 2 emission reduction: 24.5 kt/y during navigation. • Increased energy production by 697% through the Ship-to-Shore concept. • Provided a pathway for sustainable maritime propulsion aligned with IMO targets. This paper investigates the integration of IV generation small modular reactors into maritime vessels as a viable alternative to conventional fossil fuel-powered systems. To support maritime decarbonisation and evaluate the energy and economic performance of their onboard implementation, suitable mathematical models of energy systems powered by small modular reactors are developed. Among various nuclear technologies, a lead-cooled fast reactor (LFR) using mixed oxide fuel is modelled and implemented within a dynamic simulation environment. The model simulates the energy performance of a Helium Brayton cycle with a regenerator and reheating, powered by an LFR. This model can assess the temperature distribution of the lead coolant, the helium temperatures throughout the Brayton cycle, the generated mechanical and electrical power, thermodynamic efficiency, and waste heat. Following the development of the LFR-based model, it is integrated into a broader computational framework that enables the evaluation of the ship’s overall energy performance, including the energy demands of onboard utilities under different operating modes and climatic conditions. To demonstrate the potential of these systems, a LFR is simulated as a replacement for conventional fossil fuel engines onboard a containership. A representative route, reconstructed from real-time online data, is used to assess reactor performance under dynamic maritime conditions. Furthermore, a novel concept – ship-to-shore connection – is introduced, whereby surplus electricity produced by the onboard LFR is supplied to port grids, contributing to the decarbonisation of port facilities and surrounding areas. Simulation results indicate that small modular reactor systems could effectively nullify onboard fossil fuel consumption. For instance, avoided CO 2 emissions are estimated at 24.5 kt/y during navigation and 15.3 kt/y during port stays, including also emissions offset through the replacement of national thermoelectric power generation in ship-to-shore application. The implementation of the ship-to-shore connection concept results in an increase in energy production during port stays ranging from 572% to 697%, yielding substantial environmental and economic benefits.

Life cycle assessment of the solar thermal power plant integrated with air-cooled supercritical CO2 Brayton cycle

Performance analysis of a small lead-cooled fast reactor coupled with a copper-chloride cycle hydrogen production system

In this paper, a supercritical CO2 cycle concept is investigated in terms of possible use as a power conversion cycle. Three types of most popular modifications of simple Brayton cycle (pre-compression, partial cooling and recompression) are described. As the most efficient, a recompression cycle was chosen for further investigation. The model of the recompression supercritical carbon dioxide Brayton cycle was created using GateCycle software. The results of simulation performed in GateCycle software show that the cycle achieves efficiency of 44% for CO2 turbine inlet conditions of 550°C and 20 MPa. Comparison of optimum turbine inlet pressure for cycle efficiency and net output power at turbine inlet is presented.

Solar power has innate issues with weather, grid demand and time of day, which can be mitigated through use of thermal energy storage for concentrating solar power (CSP). Nuclear reactors, including lead-cooled fast reactors (LFRs), can adjust power output according to demand; but with high fixed costs and low operating costs, there may not be sufficient economic incentive to make this worthwhile. We investigate potential synergies through coupling CSP and LFR together in a single supercritical CO2 Brayton cycle and/or using the same thermal energy storage. Combining these cycles allows for the LFR to thermally charge the salt storage in the CSP cycle during low-demand periods to be dispatched when grid demand increases. The LFR/CSP coupling into one cycle is modeled to find the preferred location of the LFR heat exchanger, CSP heat exchanger, sCO2-to-salt heat exchanger (C2S), turbines, and recuperators within the supercritical CO2 Brayton cycle. Three cycle configurations have been studied: two-cycle configuration, which uses CSP and LFR heat for dedicated turbocompressors, has the highest efficiencies but with less component synergies; a combined cycle with CSP and LFR heat sources in parallel is the simplest with the lowest efficiencies; and a combined cycle with separate high-temperature recuperators for both the CSP and LFR is a compromise between efficiency and component synergies. Additionally, four thermal energy storage charging techniques are studied: the turbine positioned before C2S, requiring a high LFR outlet temperature for viability; the turbine after the C2S, reducing turbine inlet temperature and therefore power; the turbine parallel to the C2S producing moderate efficiency; and a dedicated circulator loop. While all configurations have pros and cons, use of a single cycle offers component synergies with limited efficiency penalty. Using a turbine in parallel with the C2S heat exchanger is feasible but results in a low charging efficiency, while a dedicated circulator loop offers flexibility and near-perfect heat storage efficiency but increasing cost with additional cycle components.

Study on control strategies of the MW-scale supercritical CO2 recompression Brayton cycle for lead-cooled fast reactor

This study examines the performance of a novel recompression supercritical CO2 (S-CO2) Brayton cycle of nuclear power plant with pre-cooler exergy utilization, which uses a transcritical CO2 cycle to enhance the performance of this new cycle. More attention was paid to irreversibilities generated in the combined cycle. Individual models were developed for each component through the application of the first and second laws of thermodynamics. The effects of the turbine inlet temperature, compressor pressure ratio, maximum cycle pressure, main compressor inlet temperature, and also environment temperature on the first- and second-law efficiencies and also on the exergy destruction of the S-CO2 and the presented new S-CO2 recompression cycles were studied. Finally, the recompression S-CO2 cycles were thermodynamically optimized using the Engineering Equation Solver software. Based on identical operating conditions, a comparison between the new S-CO2 and a simple S-CO2 cycle was also performed. It was found that both the first- and second-law efficiencies of the new S-CO2 cycle are about 5.5 per cent to 26 per cent higher than that of the simple S-CO2 cycle. The exergy destruction of the new S-CO2 cycle is also about 6.7 per cent to 28.8 per cent lower than that of the simple S-CO2 cycle.

The supercritical carbon dioxide (sCO2) Brayton cycle has been regarded as a promising technique for future energy conversion systems. sCO2 recompression cycle configuration has been widely studied for nuclear reactors with the temperature difference between the reactor inlet and outlet restricted to 200°C. However, this cycle configuration may be not suitable for high temperature gas-cooled reactors (HTGR) with a temperature difference up to 500°C. Herein, we aim to develop an optimal sCO2 cycle configuration for HTGR with a broad temperature span, which has both high cycle efficiency and sufficient mechanical security guaranteed by energy cascade utilization. We propose a recompression cycle combined with reheat and expansion technologies, and perform a parameter optimization in Fortran platform. First, the thermodynamic models of the system are established. Then, the parametric analysis is conducted about the effects of split ratio, temperature difference of the heat exchangers, inlet parameters of turbines and compressors, and isentropic efficiencies on the cycle performance. The sCO2 cycle tailored for HTGR can achieve a cycle efficiency of 44.98%. Our work not only highlights the design criteria of temperature-match between the HTGR and sCO2 cycle but also guides the numerical assessment of the steady-state performance.

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including high cycle efficiencies, reduced component sizing, and potential for the dry cooling option. More research is involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems for CSP applications. In this study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced, up to 50%, compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the simple recuperated and recompression Brayton cycle layouts using s-CO2 as a working fluid are evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the recompression Brayton cycle using an isothermal compressor has 0.2–1.0% point higher cycle thermal efficiency compared to its reference cycle. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency for a wider range of CIT than the reference cycle. Adopting an isothermal compressor in the s-CO2 layout can imply larger heat exchange area for the compressor which requires further development.

Synergetics: The cooperative phenomenon in multi-compressions S-CO2 power cycles