4K Hybrid Nuclear Renewable Energy Systems - Department of Energy

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4K Hybrid Nuclear Renewable Energy Systems - Department of Energy

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Quadrennial Technology Review 2015
Chapter 4: Advancing Clean Electric Power Technologies

Technology Assessments

Advanced Plant Technologies


Clean Power

Carbon Dioxide Capture and Storage Value-Added Options

Carbon Dioxide Capture for Natural Gas and Industrial Applications

Carbon Dioxide Capture Technologies

Carbon Dioxide Storage Technologies

Crosscutting Technologies in Carbon Dioxide Capture and Storage

Fast-spectrum Reactors

Geothermal Power

High Temperature Reactors

Hybrid Nuclear-Renewable Energy Systems


Light Water Reactors

Marine and Hydrokinetic Power

Nuclear Fuel Cycles

Solar Power

Stationary Fuel Cells


Supercritical Carbon Dioxide Brayton Cycle Wind Power

Quadrennial Technology Review 2015
Hybrid Nuclear-Renewable Energy Systems
Chapter 4: Technology Assessments
Introduction and Background
This Technology Assessment summarizes the current state of knowledge of nuclear-renewable hybrid energy system (N-R HES) concepts and associated technology development needs. Some of the principles addressed in this technology review may also apply to other hybrid energy systems (see Chapters 2 and 7 of the main report of the Quadrennial Technology Review). The main purpose of an N-R HES is to use nuclear energy, variable renewable energy sources such as wind and solar, biomass energy, or others as clean energy sources to support electrical and thermal duties of electricity generation, fuels production, chemical synthesis, and other industrial processes at competitive prices and to thus decrease greenhouse gas emissions (GHG) by the electricity, transportation, and industry sectors. Such hybrids would differ substantially from traditional systems that typically use just one or perhaps two energy sources (e.g., biomass co-firing with coal) to produce electricity and sometimes useful heat (cogeneration systems).
Wind and solar power generation accounted for about two-thirds of all U.S. electricity generating capacity additions in 2015. Increased penetration of variable renewable energy systems such as wind and solar PV increases the need for flexible generation—as can be provided by dispatchable intermediate and peaking units, as well as through more flexible loads—as can be provided by demand-side management, in order to maintain system voltage and frequency within limits. (Intermediate units serve the large fraction of demand between baseload units, which provide nearly constant demand 24 hours per day, and peak units, which serve the very highest demands that occur a few percent of the year or that serve demand when events such as a generator or transmission failure require the rapid response capabilities of peaking units.) Such flexible generation generally also has greater value in electricity markets than baseload or variable supplies. N-R HES may serve an important role in providing this flexibility.
Flexible N-R HES architectures of interest include the following:1 1. Tightly Coupled N-R HES: In this architecture, nuclear and renewable generation sources and industrial processes would all be linked and co-controlled behind the electricity bus, such that there would only be a single connection to the grid, as shown in Figure 4.K.1. The closely coupled system would likely be managed by a single financial entity to optimize profitability for the integrated system. 2. Thermally Coupled N-R HES: This architecture would thermally integrate subsystems and tightly couple them to the industrial processes, but the nuclear and renewable electrical subsystems could have more than one connection to the same grid balancing area and would not need to be co-located, but would be co-controlled to provide energy and ancillary services to the grid. The thermally integrated subsystems would need to meet industrial process requirements considering the required heat quality, the heat losses to the environment along the heat delivery system, and the required exclusion zone around the nuclear plant. These systems would likely be managed by a single financial entity (see Figure 4.K.2).
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3. Loosely Coupled, Electricity Only N-R HES: This configuration would be electrically coupled to industrial energy users but there would be no direct thermal coupling of subsystems. This design would allow management of the electricity produced within the system (e.g., from the nuclear plant or from renewable electricity generation) prior to the grid connection. Although there would not be a direct coupling of thermal energy to the industrial processes, the system could include electrical to thermal energy conversion equipment to provide thermal energy input to the industrial process(es). Such an option may allow for potential retrofit of existing generation facilities with fewer regulatory challenges. These systems could have more than one connection point to the grid but would likely be managed by one financial entity (see Figure 4.K.3). Molten salt reservoirs such as those currently being used to store concentrated solar energy, or a mass of firebrick similar to heat recuperators used by the steel manufacturing industry2 may provide thermal energy storage for the heat that can be generated from electricity. In principle, electrical-to-thermal energy conversion would be economical when the cost of producing heat by these systems drops below the cost of producing heat from traditional combustion-fired process heaters. The type and quality of heat must match the industrial heat user technical specifications.
Figure 4.K.1 General architecture for a tightly coupled nuclear renewable hybrid energy system, where the generation sources are integrated behind a single connection point to the grid and are managed by a single financial entity.
Credit: Idaho National Laboratory
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Figure 4.K.2 General architecture for a thermally coupled nuclear renewable hybrid energy system, where the nuclear and renewable generation sources are co-controlled and managed by a single financial entity but may not be co-located.
Credit: Idaho National Laboratory
Figure 4.K.3 General architecture for a loosely coupled (electricity only) nuclear renewable hybrid energy system, where the generation sources are only electrically connected to the industrial process. Note that electrical to thermal energy conversion systems may be included to provide thermal energy to some processes.
Credit: Idaho National Laboratory
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The following major components would be present in each of the illustrative N-R HES:  Nuclear reactor(s). The nuclear reactor would provide baseload heat and power without direct3 emission of GHGs. The nuclear system should operate at a high capacity factor to cover capital and operating costs. The reactor(s) would also perform more efficiently and maintenance costs would be minimized if operated near steady state design conditions. Nuclear generated heat would be apportioned to the industrial process and storage, to the power generation system, and to fuels production (such as hydrogen) based on net loads and optimum earnings.
 Power generation. The steam turbine in the power generation subsystem would convert thermal energy generated by the nuclear reactor into electrical power. The amount of power generated could be ramped up or down depending on the amount of steam dispatched to it; hence, it would be a flexible generator of electricity. The other thermal energy produced by the nuclear reactor could be used for industrial processes, fuels production, or stored. Steam turbines’ large mass provides significant rotational inertia, and together with the synchronous generators they drive, they could help support grid frequency stability.
 Renewable energy generator(s). The renewable source(s) would provide near-zero marginal cost energy (heat and/or power) without direct emission of GHGs. Generation by variable renewable technologies (i.e., solar photovoltaic [PV] and wind), however, is not substantially dispatchable, meaning that it cannot provide large amounts of power as needed to follow grid load. Electricity and heat from renewable energy sources could also be used by the industrial process, fuels production, or stored.
 Industrial process. When coupled within an N-R HES, the industrial process would receive heat and/ or power from the nuclear reactor(s) and the renewable energy source(s) as needed or as available. The system would use that energy to produce high value products or fuels that would provide another income stream for the N-R HES. When heat from the nuclear reactor is diverted to power production, the heat needed by the industrial process could be provided by stored thermal energy or derived from another clean energy source such as a biomass boiler when constant operation of the industrial process is necessary or desired.
N-R HES differ from combined heat and power systems to the extent that the goal is not solely cogeneration of heat and power for local industrial plant uses; rather, the goals also include the transfer of as much low-carbon energy to the industrial process as possible. N-R HES are essentially a cooptimization approach to support grid reliability and stability and to support industrial production, providing power generation and thermal energy to industry while maximizing profitability and minimizing GHG emissions. Details on DOE’s CHP research activities can be found on the DOE-EERE home pages.4
With the advent of Small Modular Reactors and Concentrating Solar Thermal Power (CSP) systems, the potential exists to apply these to CHP applications in the traditional manner where heat generation is located in proximity to the industrial process. DOE is currently completing a technical assessment of heat markets in the U.S. Opportunities for nuclear and renewable energy sources for heat applications are currently being evaluated.5  Storage (electrical, thermal, and/or chemical).6 Electrical storage options include batteries and flywheels. Thermal storage options include both liquid (e.g., molten salt) and solid (e.g., firebrick) forms.7 Chemical storage could include hydrogen production, such as through thermally-assisted electrolysis. Heat removed from storage could be used either directly in the industrial process or to generate power.
Tightly coupled and thermally coupled N-R HES concepts would require a dual heat delivery system and the controls necessary to apportion heat between power production, a given industrial process, or fuels production. Similarly, the electrical output would be apportioned between the grid, the coupled industrial process, or fuels production. If necessary, power would be drawn from the grid and combined with the heat and/or electricity delivered from within the hybrid system to operate the industrial process. In the thermally coupled case, the
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renewable subsystem could be loosely coupled and operated in close coordination with the nuclear subsystem via the grid balancing area. Thermal energy generators (e.g., nuclear reactor and CSP) could supply heat, steam, and power to the manufacturing industry or power to the grid, apportioned to maximize earnings. These systems could operate as dynamic cogeneration plants, adjusting output to meet grid needs and to maintain economic operation of the overall plant.
By comparison, traditional nuclear power plants typically connect to the grid alone.8 Interaction between generators is variously managed by independent system operators (ISO), Regional Transmission Organizations (RTO), utilities, cooperatives, Federal systems, etc., depending on the location and level.
Successfully developed, N-R HES could potentially provide significant benefits, including:  Reducing the cost and volatility of energy production, particularly by helping balance electricity supplies from variable renewable sources;  Providing dispatchable, carbon-free electricity generation for the grid, with little to no impact on the nuclear reactor operations profile which can have technical impacts on the core, fuels, and heat transfer loops;  Providing more efficient utilization of capital equipment by providing a second customer for the heat that can be generated by the nuclear reactor, which at some point may be lower cost than producing heat from combustion sources;  Providing greater grid support than variable renewable sources alone;  Reducing the carbon footprint of the industrial sector; and  Reducing energy system impact on fresh water resources when using excess thermal or electrical energy to produce potable water, and by coupling low temperature heat rejection to an industrial heat user rather than relying on a cooling tower to condense the power cycle water.
Matching Energy Capacity and Energy Markets
In 2014, the U.S. electrical power generation capacity exceeded 1,068 GW.9 In this same year, U.S. electricity consumption totaled 3,900 billion kWh in sales to end users,10 or about 450 GW on a continuous output basis. This indicates a significant amount of the overall power generation capacity (about 60%) is idle for substantial periods during the year. Depending on the season of the year and diurnal use patterns, the location and type of power generation facilities, and the disposition of hydro and variable electricity generation sources, a significant percentage of the power generation capacity could, in principle, be directed part-time to industrial processes. Initial estimates indicate that about one-third of the current power generation resources could be re-directed to manufacturing and fuels production.11 Hybrid energy systems look to expand thermal and power generation to industrial manufacturing and fuels production with better overall capacity utilization. With the build-out of renewable power, hybrid systems could offer an alternative off-take for baseload nuclear plants that are optimally operated at their name plate capacity. Additionally, hybrid systems may offer another option for managing the electricity that will be produced by renewable energy sources.
Market opportunities to apply a large amount of energy on a variable basis have been presented in recent publications by researchers at the Massachusetts Institute of Technology (MIT), Idaho National Laboratory (INL), and the National Renewable Energy Laboratory (NREL).12, 13, 14, 15 A breakdown of the energy use of the top six industrial energy users is summarized in Table 4.K.1. Other industries with large energy use include inorganic minerals production (cement, phosphates, sodium carbonates, silica, etc.), textiles, glass, and computers and electronics. Prime opportunities for using N-R HES include industrial plants that have high steam duties and processes that require low to intermediate temperature heat. Small modular reactors (SMR) are an appropriate size to service some of these plants and could be located near these end users to service them.
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Table 4.K.1 Annual Energy Use of the Six Largest U.S. Industrial Users of Energy in Exajoules (EJ)16

Chemicals Petroleum Refining Forest Products Iron & Steel Mills Food & Beverage Mining Total (EJ)

EJ Electrical 1.1 0.3 0.8 0.2 0.3 0.7 3.4

EJ Steam Systems 1.7 1.1 2.6 0.1 0.6 0.03 6.1

EJ Fired Heaters 1.3 2.2 0.2 1.5 0.3 0.2 5.7

EJ Total by Industry 4.1 3.6 3.6 1.8 1.2 0.9 15.2

The benefits of SMRs potentially include reduced manufacturing costs, safety advantages, incremental scalability, reduced land use, and, in the case of high temperature reactors, reduced water usage.17 Some designs provide passively-safe, gravity-driven, natural circulation through the primary core. Some designs are submerged in the coolant pool to provide long term to permanent emergency cooling and some are below ground to be more tolerant of physical damage by earthquakes or tornados. Multiple barriers are designed-in to prevent the release of radiation should an accident occur and could potentially allow an SMR to be located adjacent to an industrial user, and in closer proximity to population centers.18
Flexible operations could also enable production of clean water from saline or compromised water sources for use in power plant, industrial, or even community services. Water desalination is one option for flexible operation of an existing plant or for future SMRs.19 The IAEA has an on-going program to address the issues related to the use of nuclear energy for desalination of alternative sources of water, including wastewater from municipalities, agricultural runoff, brackish groundwater, or seawater.20 A recent study of a N-R HES indicates fresh water may be efficiently and cost-effectively produced from brackish water in the Southwest U.S. when future demands exceed fresh water availability.21 Clean-up of water displaced from deep saline aquifers by future CO2 injection into these reservoirs to sequester the carbon is another potential application. Low-rank coal drying could release significant by-product water that could be cleaned and used for other purposes.
New energy systems might also be integrated with process heat applications.22 This could, for example, reduce the water cooling requirements of SMRs that are located in proximity of the heat application. Such cases could operate like a traditional CHP system where the SMR is located near the industrial heat user, such as for inorganic minerals concentration and drying, or for distiller grain drying and for distillation in corn-ethanol plants. Other less apparent industrial uses might include paper pulp operations (~10-20 MWt is typical), food processing plants (~5-20 MWt is typical), and chemical plants (e.g. methanol distillation), with a typical plant using 100 MWe and 90 MWt).23
The reactor design could be optimized for a particular industrial service, considering the process heating requirements relative to scale, peak temperature, steam quality, time-of-use, overall conversion efficiency, and other factors. In some cases thermal energy storage in a steam accumulator or a molten salt or liquid metal tank could be used to buffer the thermal/electrical energy available from the N-R HES or from the grid. Technical assessment of the scale, duty cycles, and associated costs of thermal energy storage buffers is needed for future DOE or industrial consideration of possible hybrid configurations. Hybridization options will vary in accordance with regional resources, industry, electricity, and financial markets.

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Nuclear Hybrid Energy System Configurations
Figure 4.K.4 illustrates possible industrial opportunities for N-R HES. The design basis for these depends on case-specific industrial user technical requirements and economic drivers associated with these or other options. Systems should be tailored to regional resources and markets to dynamically optimize the use of thermal and electrical energy. Definition, prioritization, and analysis of key options based on pertinent figures of merit are necessary to identify energy systems that have the greatest likelihood for success.

Figure 4.K.4 Summary of potential N-R HES applications indicating energy conversion varieties possible and their appurtenant processes.24, 25 Heat transfer distances are only an approximation based on preliminary calculation under the Next Generation Nuclear Plant (NGNP) Program.26 Arrows indicate energy flows. Color is only intended for graphical rendering.
Credit: Idaho National Laboratory

Mechanical Processes
Flow-Through Battery

Centralized or Distributed Energy
Storage • Pumped Hydro Power • Compressed Air • Refrigerant cooling • Gas separation units
Electricity Grid

<0.5 km Local Thermal Energy Storage and Recovery

Power Gen Set

Nuclear or Renewable Heat Source

<1 km; < 850 °C
• Steam Methane Reforming
• Hydrothermal Biomass Gasification
• Sulfur-Iodine Water Splitting
• < 600 ° C Processes

< 3 km; < 600 °C
• Biomass and Coal Pyrolysis
• Petroleum Crude Distillation; HydrogenCracking and Treatment
• Oil Shale Retorting • < 300 °C Processes

Heat Circulator

Thermal Processes

Local or Distributed Load Demand Capacity and Power Regulation
• Electric Vehicle Charging
• Distributed Thermal Energy Storage
• Reverse Osmosis Water Desalination
• PEM Electrolysis & Hydrolysis
• Minerals Reduction • Electro Refining • Electric-Arch Furnace • Plasma Reforming
Electrical Processes

Tightly Coupled • Distributed Hydrogen
and Oxygen Generation by Water Splitting • Forward Osmosis Water Desalination • Multi-Effect ZeroLiquid Discharge
Thermo-Electrical Processes

< 10 km; < 300 °C
• Steam Electrolysis • Steam-Assisted Gravity
Drainage • Petroleum Refining • Inorganic Minerals
Concentration/Drying • Ethanol Distillation • Forest and Paper
Products • Food Processing • Coal & Biomass Drying

< 100 km; < 100 °C
• District Heating • Chilled Water
Production • Algae Production • Geothermal Heating

Thermal Fluid
Manufacturing • Polymers & Textiles • Fertilizers • Industry Fired Heaters • Metals Reduction/Annealing

Distributed Thermal Energy Storage
Distributed H2 & O2
Chemical Processes

Thermal Fluid
Fuels • Petroleum Refineries • Biofuels Refineries • Diesel & Gasoline Blending • Fuel Cell Vehicles

Heat delivery to meet end user requirements depends on the physical properties and temperature of the heat transfer fluid and the design of the thermal hydraulics system. Temperature and distance comparisons are indicative of the challenges of distributing heat at a specific temperature (and for a particular working fluid and heat exchanger) from a nuclear reactor to an industrial user. The distances shown are an initial approximation of the distances that various heat levels can be economically circulated for heat deposition at the industrial user site. Actual distances will vary depending on design and economics of the system. Direct (or tight) coupling with the industrial user can include purely thermal energy, purely electrical energy, or a combination of the two. Thermal, electrical (e.g., Compressed Air Energy Storage, Battery Storage), and chemical derived energy can be stored and then delivered to industry when needed.
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Previous DOE efforts have included technical and economic evaluation of the use of nuclear heat for cogeneration applications under the Next Generation Nuclear Plant (NGNP) program.27, 28 The NGNP Alliance with industry continues to develop heat application markets for the high temperature gas reactor (HTGR) with an outlet of approximately 750°C helium based on current code-qualified materials. The results of these studies indicated one or more of the nominal 600 MWt plants could supply the quality and quantity of heat needed for steam methane reforming to produce hydrogen, ammonia and ammonia-based derivatives (ammonia-based fertilizers, nitric acid, urea), synthetic chemicals, and non-conventional fuels (from oil sands, oil shale, coal, and natural gas). Although the capital investment for a nuclear plant is comparatively higher than traditional fossil-fired heat sources and steam boilers, the analysis indicates that heat produced from nuclear reactors could favorably compete if fossil fuels combustion took into account estimated externality costs of GHG emissions.
Currently, N-R HES applications for all classes of reactors are being investigated by the DOE Office of Nuclear Energy (DOE-NE). Program milestone reports compare the differences between potential N-R HES applications in the electrical power market with coordinated synthesis of methanol from natural gas and hydrogen production through high temperature steam electrolysis, as two examples representing large chemical industries in the United States.29, 30
In a project that is coordinated between DOE-NE and DOE-Energy Efficiency and Renewable Energy (DOEEERE), the value proposition and technical integration challenges of nuclear and renewable energy in hybrid systems are being evaluated.31 Two regional cases were selected for detailed evaluation in West Texas, where wind and natural gas are plentiful, and in northeast Arizona, where solar energy is abundant and brackish water can be purified for potable use. These studies are intended to help identify the hybrid systems R&D needs, and some of the findings are provided below.
Nuclear Hybrid Energy System Example
In evaluating N-R HES, the first question that arises is, “Can electricity and heat be manipulated in a dynamic manner that corresponds to the ramp-up or ramp-down demands of grid load-following power generation dynamics?” The second question becomes, “How efficient is the utilization of capital investments?” The latter question should be cast relative to alternative capital investments that are required to accommodate the variability of renewable energy sources, whether the capital investments are new transmission and distribution lines for wider area balancing control, storage, demand response agents (i.e., meters and controls), or hybrid energy systems components.
Figure 4.K.5 illustrates the coupling of nuclear and wind to produce power in response to grid demand up to the maximum generation capacity of the combined resources, and to produce hydrogen by steam electrolysis when demand for electricity falls below the capacity of the system.32 In this illustrative example, power generation was assumed to be the highest priority, even when the market may actually drive the systems to produce hydrogen any time the value of hydrogen is higher than electricity.
In general, a loosely coupled, electricity-only HES involves only power production with multiple generators supplying a single output of electricity to the electrical grid-as described in a recent DOE report.33 The “advanced hybrid energy system” defined within this study falls into the category of a thermally coupled HES through the addition of time-varying hydrogen production when heat and electricity are transferred to the steam electrolysis plant, creating a second product output.
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Figure 4.K.5 Possible configuration for a traditional hybrid energy system (yellow box) versus an advanced hybrid energy system (large box).34
Credit: Idaho National Laboratory

Advanced Hybrid Energy System Traditional Hybrid Energy System


Nuclear Energy

Electricity Storage

Point of Common Coupling

Power Grid

Thermal Energy

Power Generation

Electrical Energy


High Temperature Electrolysis

Hydrogen Oxygen


Hydrogen and Oxygen Production Plant

Chemical Products (e.g. H2, O2)

A transient physics-based model was developed to address the technical feasibility of shifting electricity and heat to the electrolysis unit based on a representative wind farm operating in Wyoming, and a load profile representative of the Midwest.35, 36 The dynamic simulation for this case demonstrated that the advanced nuclear hybrid solution is physically capable of resolving the power generation variability introduced by wind turbines down to a minute-by-minute time scale. The electrical battery storage unit helped smooth the transients associated with power generation spin-up and spin-down. The electrolysis unit, with gas flow and heat recuperation, is also capable of being operated intermittently as functionally required. Physical testing of this modeled outcome is needed to confirm these conclusions.
In order to address the question regarding economic viability, the ratio of cash flows (computed as the profitability of the system as a percentage of the total wind power generation in the system) was calculated for both the traditional and the advanced HES. The ratio of profitability (referred to as the Profitability Index, or PI) is plotted in Figure 4.K.6. When PI is less than 1.0, then the additional profit gained by operating the electrolysis unit does not justify the additional capital investment for this unit. In other words, the rate of return on investment for the advanced system would be less than construction and operation of only the traditional HES when PI < 1.
For the example considered, when the wind capacity exceeded 23 percent, the additional revenue for hydrogen production from excess generation that would otherwise be curtailed (assuming commodity prices of $2.50/ kg-H2 at the plant gate and $0.12/kWh electricity) was sufficient to cover the cost of capital and operating costs
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