Hydrogen production using high temperature nuclear reactors: Efficiency analysis of a combined cycle

In the present work, the feasibility of using a high temperature gas cooled nuclear reactor (HTR) for electricity generation and hydrogen production are analysed. The HTR is combined with a steam and a gas turbine, as well as with the system for heat delivery for medium temperature hydrogen production. Industrial-scale hydrogen production using copper-chlorine (Cu-Cl) thermochemical cycle is considered and compared with high temperature electrolysis. Presented cycle shows a very promising route for continuous, efficient, large-scale and environmentally benign hydrogen production without CO2 emissions. The results show that the integration of a high temperature helium reactor, with a combined cycle for electric power generation and hydrogen production, may reach very high efficiency and could possibly lead to a significant decrease of hydrogen production costs.

Nuclear powered heat pumps for near-term process heat applications

This concept shows that an efficient combined cycle, comprising topping & bottoming cycle, does not have to be privilege of gas turbine plants only, but could also be achieved with steam turbine plants. An efficient power-producing concept of a combined steam-turbine cycle with addition of a recirculating steam compressor is disclosed. Topping part of such a combined steam-turbine cycle operates at elevated steam turbine inlet temperature and pressure, while its “waste heat” is recovered by the bottoming part of the combined cycle in a heat-recovery boiler (steam heat exchanger). The recirculating steam compressor pumps the cooled majority of the entire steam flow to the maximum cycle pressure, while smaller steam flow fraction continues its full expansion to some low pressure in a condenser. The cycle waste heat could be transferred to the bottoming part of the combined cycle in a variety of modalities, depending on the chosen main high-temperature steam-turbine inlet temperature and inlet pressure (supercritical/subcritical). At an assumed constant steam-turbine inlet temperature of 900°C (∼300 bar), a very high gross cycle thermal efficiency could potentially be achieved, ranging from 56 to 62% with the high-temperature steam-turbine pressure ranging from subcritical (30 bar) to supercritical (300 bar). Such a combined steam-turbine cycle seems to be a suitable energy conversion concept that could be applied in classic thermal power plants powered by coal, but also seems as an ideal option for application in the new generation of gas-cooled nuclear rectors, where the gaseous reactor coolant, heated up to 1000°C, would indirectly transfer its heat content to working fluid (superheated steam) of the topping part of the combined steam-turbine cycle. Alternatively, the proposed concept may be combined with renewable energy sources of a sufficient temperature level.

The project supported the Nuclear Regulatory Commission (NRC) in identifying and evaluating the regulatory implications concerning the control and protection systems proposed for use in the Department of Energy's (DOE) Next-Generation Nuclear Plant (NGNP). The NGNP, using modular high-temperature gas-cooled reactor (HTGR) technology, is to provide commercial industries with electricity and high-temperature process heat for industrial processes such as hydrogen production. Process heat temperatures range from 700 to 950 C, and for the upper range of these operation temperatures, the modular HTGR is sometimes referred to as the Very High Temperature Reactor or VHTR. Initial NGNP designs are for operation in the lower temperature range. The defining safety characteristic of the modular HTGR is that its primary defense against serious accidents is to be achieved through its inherent properties of the fuel and core. Because of its strong negative temperature coefficient of reactivity and the capability of the fuel to withstand high temperatures, fast-acting active safety systems or prompt operator actions should not be required to prevent significant fuel failure and fission product release. The plant is designed such that its inherent features should provide adequate protection despite operational errors or equipment failure. Figure 1 shows an example modular HTGR layout (prismatic core version), where its inlet coolant enters the reactor vessel at the bottom, traversing up the sides to the top plenum, down-flow through an annular core, and exiting from the lower plenum (hot duct). This research provided NRC staff with (a) insights and knowledge about the control and protection systems for the NGNP and VHTR, (b) information on the technologies/approaches under consideration for use in the reactor and process heat applications, (c) guidelines for the design of highly integrated control rooms, (d) consideration for modeling of control and protection system designs for VHTR, and (e) input for developing the bases for possible new regulatory guidance to assist in the review of an NGNP license application. This NRC project also evaluated reactor and process heat application plant simulation models employed in the protection and control system designs for various plant operational modes and accidents, including providing information about the models themselves, and the appropriateness of the application of the models for control and protection system studies. A companion project for the NRC focused on the potential for new instrumentation that would be unique to modular HTGRs, as compared to light-water reactors (LWRs), due to both the higher temperature ranges and the inherent safety features.

The progress in the technology of conventional power plants with gas, steam and combined cycles suggests investigating to what extent such technology can be applied to power conversion systems for high-temperature reactors (HTR). HTR power conversion systems with steam cycle, offer the possibility of achieving steam parameters equivalent to those of currently constructed or planned conventional plants of similar high efficiency. Gas turbine and combined cycles also offer interesting prospects for obtaining high efficiency. This study, which is restricted to thermodynamic aspects, investigates the potential for increased efficiency in HTR module plants with 200 MWth. Steam and gas turbine cycles, with and without intermediate heat exchangers, and combined gas turbine/steam cycles, with and without intermediate heat exchangers, are investigated.

There exists a significant and growing need for clean, efficient, and large-scale hydrogen production. Using high temperature heat, thermochemical cycles can provide an energy-efficient route for hydrogen production. The Hybrid Sulfur process is a promising thermochemical watersplitting cycle with global-scale hydrogen production potential. The SO2-depolarized electrolyzer (SDE) is a critical component of the cycle. At the core of the electrolyzer is the membraneelectrode assembly, which consists of a solid electrolyte membrane sandwiched between two electrocatalyst layers. New electrocatalyst and membrane materials are being developed with the goals of improving the electrolyzer performance and extending the lifetime of the membrane-electrode assembly. A high-throughput methodology is being developed to screen potential candidates based on Pt and Au thin films prepared through physical vapor deposition. SO2 oxidation reaction kinetics are being analyzed for the novel catalysts and compared to the state-of-the-art, Pt/C. In addition, advanced polymer electrolyte membranes of polybenzimidazole (PBI) are utilized, which have shown superior performance in comparison to the state-of-the-art, Nafion®. These catalysts and membranes will be combined to produce high performance membrane-electrode assemblies.

Hydrogen is a commercially important element. Basically, there are several methods of hydrogen production that have been commercially used, such as Steam Methane Reforming (SMR), High Temperature Steam Electrolysis (HTSE), and thermochemical cycles, like Sulphur-Iodine (SI). Among these methods, SMR is the most widely used for large-scale hydrogen production, with conversion efficiency between 74–85% and it has commercially used in some fertilizer industries in Indonesia. Steam reforming is a method to convert alkane (natural gas) compounds to hydrogen and carbon dioxide (synthetic gas) by adding moisture at high pressure and temperature (35-40 bar; 800-900°C). These hydrogen production technologies can be coupled with different nuclear reactors based on the heat required in the process. The High Temperature Gas-cooled Reactor (HTGR) using helium as a coolant, has a high outlet temperature (900°C), so it can potentially be used to supply for process heat for hydrogen production, coal liquefaction/gasification or for other industrial processes requiring high temperature heat. Hydrogen production cost from SMR method is influenced by a range of technical and economic factors. The fuel component of natural gas needed in the SMR method can be replaced by nuclear heat from a nuclear power plant (NPP) operating in cogeneration mode (i.e. simultaneous producing electric power and heat), hence contributing to the reduction of carbon dioxide in the process.In the SMR method, fuel costs are the largest cost component, accounting for between 45% and 75% of production costs. Therefore, there is opportune to assess the economics of hydrogen production by using nuclear heat. The economic evaluation is done by using IAEA HEEP-4 Software.The results comprise cost break up for 2 cases, coupling SMR process for hydrogen production with: (1) 2 HTGRs of 170 MWth/unit; and (2) 1 HTGR of 600 MWth/unit. The cost of hydrogen production is highly depend on the scale of the NPP as energy source and results indicated that hydrogen production cost of the 1 HTGR Unit600 MWth (Case 2) has a lower value (1.72 US$/kgH2), than the cost obtained when 2 HTGR units of 170 MWth each (case 1) are considered (2.72 US$/kgH2). For comparison, the hydrogen production cost by using SMR with carbon capture and storage (CCS) with natural gas as fuel is 2.27 US$/kgH2.

Scenario analysis of gasification process application in electrical energy-freshwater generation from heavy fuel oil, thermodynamic, economic and environmental assessment

Japan Atomic Energy Agency (JAEA) has started a conceptual design of a small-sized HTGR for steam supply and electricity generation (HTR50S) to deploy the high temperature gas cooled reactor (HTGR) in developing countries at an early date (i.e., in the 2030s). Its reactor power is 50MWt and the reactor outlet temperature is 750°C. It is a first-of-kind of the commercial plant or a demonstration plant of a small-sized HTGR system for steam supply to the industries and the district heating, and electricity generation using a steam turbine. The design philosophy of the HTR50S is to upgrade the performance from the Japanese first HTGR (HTTR) and to reduce the cost for the commercialization by utilizing the knowledge obtained by the HTTR operation and the design of an advanced commercial plant of 600 MWt-class Very High Temperature Reactor (GTHTR300 series). The major specifications of the HTR50S were determined based on its design philosophy. And the targets of the technology demonstration using the HTR50S for the future commercial small-sized HTGR were identified. The system design of HTR50S was performed to offer the capability of electricity generation, cogeneration of electricity and steam for a district heating and industries. The market potential for the small-sized HTGR in the developing countries was evaluated for the application of the electricity, process heat, district heating and pure water production. It was confirmed that there is enough market potential for the small-sized HTGR in the developing countries. This paper described the major specification and system design of the HTR50S and the market potential for the small-sized HTGR in the developing countries.

In Bangladesh, the rising demand for electrical energy is a notable feature. Most of this energy is needed for domestic and industrial appliance electrical machineries and electric traction. Bangladesh has a huge population with increasing demand for electricity. The importance of electricity in everyday life in Bangladesh has reached such a stage that it is required to protect the power system from harm during fault conditions and to ensure maximum continuity of electricity supply. The power system of Bangladesh is facing several problems which are causing deficiency of electricity generation. The problems are such as: low production of electricity than the actual demand, faulty power system, lacking of natural resources required for electricity generation etc. This paper gives a brief description about the efficiency of combined cycle and single cycle power stations and shows the comparison between them to analyze that whether combined cycle power plants are more efficient for Bangladesh or not. This paper also discusses about the problems in electricity generation in Bangladesh and how to mitigate the desired electricity production by solving these problems. Using combined cycle is a wise choice as the heat energy which is produced in the gas turbine is re-used to boil the water into steam and supply the steam into the steam turbine to produce additional electricity. So, the combined cycle power station is the better option for electricity generation in Bangladesh. The main objective of this paper is to discuss the development, importance, challenges, progress and prospects of combined cycle power plants in Bangladesh.

A reverse electrodialysis cell-modified photocatalytic fuel cell for efficient electricity and hydrogen generation from the degradation of refractory organic pollutants.

The recently a large number of various companies from the energy sector have to follow new very restrictive regulations which protect the natural environment against pollution and degradation. At the same time, the efficiency of energy conversion and the cost of energy remain important economic aspects. One of the solutions for today's challenges can be power generation based on Gas Turbine Combined Cycle proposed in this paper which is the most efficient and environmentally friendly cycle. What is more important this solution can be easily integrated with a High-Temperature nuclear Reactor. The proposed in this work systems consist of the reactor combined with a gas turbine as well as steam turbine. The results show that it is possible to obtain for proposed cycle an efficiency higher than 50% which is not only more than could be offered by traditional coal power plant but much more than can be proposed by any other nuclear technology.

Hydrogen is one of the most promising alternatives as a replacement for the fossil fuels, since it can be produced by several methods using numerous sources. Sustainable production of hydrogen is highly dependent on the energy source utilized. Nuclear and renewable energy resources are considered as the best candidates for sustainable hydrogen production. Although there are numerous methods possible for hydrogen production, cost and economic factors play a crucial role in the feasibility and applicability of such plants. In this study, cost assessment of nuclear hydrogen production methods can be comparatively evaluated using Hydrogen Economy Evaluation Programme (HEEP) provided by International Atomic Energy Agency (IAEA). HEEP software is a user friendly cost estimation package, including various nuclear reactor options, as well as hydrogen generation, storage and transportation facilities. Rather than the existing data, HEEP offers user defined options from energy source to end user. Futhermore, hybrid sulfur (HyS) thermochemical cycle and high temperature steam electrolysis (HTSE) hydrogen generation systems are compared using high temperature reactors by considering storage and transportation options. The results show that the cost of hydrogen from HyS is 20 % lower than that of HTSE. HTSE requires more power consumption than HyS cycle, which has the highest impact of plant and production costs.

A two-step thermochemical cycle for solar hydrogen production using mixed iron oxides as the metal oxide redox system has been investigated. The ferrite is coated on a honeycomb structure, which serves as the absorber for solar irradiation and provides the surface for the chemical reaction. Coated honeycomb structures have already been tested in a solar receiver reactor in the solar furnace of DLR in Cologne with respect to their water splitting capability and their long-term stability. The concept of this new reactor design has proven feasible and constant hydrogen production during repeated cycles has been shown. For a further optimization of the process and in order to gain reliable performance predictions more information about the process especially concerning the kinetics of the oxidation and the reduction step are essential. To examine the hydrogen production during the water splitting step a test rig has been built up on a laboratory scale. In this test rig small coated honeycombs are heated by an electric furnace. The honeycomb is placed inside a tube reactor and can be flushed with water vapour or with an inert gas. A homogeneous temperature within the sample is reached and testing conditions are reproducible. Through analysis of the product gas the hydrogen production is monitored and a reaction rate describing the hydrogen production rate per gram ferrite can be formulated. Using this test set-up, SiC honeycombs coated with zinc ferrite have been tested. The influences of the temperature and the water concentration on the hydrogen production during the water splitting step have been investigated. An analysis of the ferrite conversion was performed using the Shrinking Core Model. A mathematical approach for the peak reaction rate at the beginning of the water splitting step was formulated and the activation energy was calculated from the experimental data. An activation energy of 110 kJ mol−1 was found. Copyright © 2009 John Wiley & Sons, Ltd.

Uranium thermochemical cycle used for hydrogen production