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Although practical experience of deploying small reactors is thin on the ground, an analysis tool presented by INL in a new report aims to reveal the economic case for deployment in microgrid applications.

The Net-Zero Microgrid Program Project report: Small Reactors in Microgrids, details the most important technical and economic considerations for can assessment of the costs and operational characteristics that inform the investment case for small reactors. As a result, the model can be used for analysing multiple scenarios to establish metrics for cost-competitive and zero-carbon microgrids that are either connected to the grid or islanded systems.

The INL model is a product of the NZM Program at Idaho National Laboratory, supported by the Department of Energy (DOE), Office of Electricity (OE). It allows developers to explore the capabilities, constraints, and nuances of small reactors by incorporating parameters related to plant economics, design efficiency and performance, plant operation, and fuel supply. Reactor technology qualities include parameters such as electricity, heat extraction, and thermal storage, while other factors include items such as financial costs and incentives. The goal of the model is to provide guidance for the selection of small reactor technology suitable for different applications and deployment scenarios and as a path forward for techno-economic studies of small reactors that are integrated with generation using renewable energy and storage in microgrids.

Modelling small reactors

The INL assessment notes that small reactors have unique cost and operational characteristics that differentiate them from other generation technologies commonly employed in microgrids. These characteristic features include but are not limited to, extended refuelling cycles, decommissioning costs, modes of power variation, and combined heat and power (CHP) operations. The INL authors say these need to be recognised when modelling them as generators in microgrids. These characteristics must be accounted for in microgrid dispatch and planning decisions as they interact with loads, storage, and other generation technologies.

To model these interactions within a microgrid decision-support platform, a small reactor model has been added to the existing Xendee platform, which can model and control more than 25 technologies and 14 distinct value streams such as electric vehicle charging and demand charge reduction.

An informed techno-economic decision-making platform built on scientific models, Xendee captures steps needed to optimise the design and implementation microgrids, community energy projects, and distributed energy resource projects. Xendee also supports the operations and dispatch of microgrids by guaranteeing the reliability, resilience, and practical boundary conditions of such projects.

The small reactor unit not only inherits features of conventional generation technologies such as unit-install costs, minimum loading, and ramp-rate limits but adds unique features including fuel cost for every refuelling period and end of life decommissioning costs.

The report notes that unlike other generation sources, such as gas turbines that rely on continuous fuel supplies, nuclear fuels can last significantly long periods. Therefore, refuelling in nuclear power plants occurs at discrete time intervals with distinct front- and back-end processes. The fuel cost is therefore defined by front- and back-end costs. The front-end fuel cost encompasses all the expenses related to loading nuclear fuel, including the cost of natural raw uranium and the costs associated with conversion, enrichment, fabrication, and fuel loading. On the other hand, back-end fuel cost refers to the expenses associated with handling spent fuel and nuclear waste, which includes interim storage, transport, and disposal. The front-end fuel cost is added to the capital expense as part of the investment-year costs. Succeeding fuel costs are part of the operational expense (OPEX). Both front- and back-end costs are incurred after every refuelling period.

Similarly, the report notes the decommissioning cost of a nuclear plant encompasses the expenses involved in dismantling the facility after its operational lifespan has ended. These costs typically encompass expenses related to the shutdown of the reactor, repurposing of the facility, and demolition. Additionally, it encompasses the final instance of the back-end fuel cost incurred at the end of the reactor’s last refuelling.

The Xendee small reactor model also includes an option for baseload operation, electricity and heat output that can be traded, and reactor power manoeuvring and cycling limits.

Considering unique features

Along with characterisation of feature that are unique to small reactors, the Xendee platform also addresses the capabilities of a complete net-zero microgrid (NZM) including a small reactor module with electricity, heat extraction and thermal storage. The model captures the most important technical and economic considerations for the specific analysis of the small reactor element: cost and operational characteristics, as well as financial costs and incentives. The model can analyse multiple scenarios to establish metrics for cost-competitive and zero-carbon microgrids either connected to the grid or completely isolated. The model is fully integrated with the Xendee analysis of clean energy microgrids alongside storage and generation from renewable energy resources and includes the capabilities, constraints, and nuances of small reactors by incorporating parameters related to plant economics, design efficiency and performance, plant operation and component and fuel lifespan.

According to the INL report, the cost parameters also recognise advanced nuclear technology for modular production and installation based on economies of scale from factory manufacture and related commissioning. This includes cost reduction as the technology matures from first-of-a-kind (FOAK) through to nth-of-a-kind (NOAK) deployments. The cost parameters include installation, operations and maintenance, fuel cycle, and reactor life. Installation cost reflects economies of scale due to unit sizing at scale and colocation. Operations and maintenance (O&M) consider economies of scale for both fixed- and variable-cost fuel life-cycle costs that are incurred at every refuelling interval as well as waste-handling and disposition costs.

The INL report also investigates key characteristics of different small reactor technologies suitable for microgrid applications, including design principles, sizing, coolant properties, temperature ratings, fuel structures, and life-cycle considerations. This also includes fuel technologies applicable to these various reactor systems, alongside strategies for nuclear waste and spent-fuel management and approaches to address safety, security, and proliferation challenges. Four primary groups of reactor technologies are examined: water-cooled, liquid-metal-cooled, high-temperature gas-cooled, and molten-salt-cooled systems.

Technology selection

An initial guideline for technology selection is also included within the report. In aligning the characteristics of the technologies with the requirements of microgrids the report notes the selection of technology in a microgrid is influenced by various factors. These include financial capacity, location and accessibility, demand type and characteristics, reliability and resilience requirements, area constraints, and the lifespan of the microgrid. The types of electrical and non-electrical applications within the microgrid also play a significant role in technology selection. The characteristics of small reactors, such as their smaller size, modularity, transportability, long refuelling interval, improved safety features, ability to operate in autonomous or semi-autonomous mode, and provision of high-grade heat, are particularly appealing for microgrids, the INL authors conclude.

The model has also been created to be continuously improved with the acquisition of actual data on investment and operational costs, experience with supply chains, production at scale, and field deployments. In the near term, performance data on applications in microgrids will become available from laboratory tests, such as those planned in the INL-led Microreactor Applications Research Validation and Evaluation (MARVEL) project.

The model incorporates scenario data and known reactor design specifications, enabling techno-economic analysis for their deployment in microgrids. It specifically considers the distinctive attributes of small reactors as generators and they. can be modelled and analysed in the context of generation from renewable energy sources, energy storage, and flexible loads over a range of applications and functions. The tool thus offers a comprehensive approach for feasibility studies, scenario development, and sensitivity analysis for “what-if” consideration of any range of assumptions about the deployment of small reactors in microgrids and other aggregations of distributed energy resources, including virtual power plants. Ultimately,

Ultimately, the analysis tool allows small reactors to be recognised as a carbon-free energy source for electricity and heat generation that is necessary for microgrids to transition away from the carbon-based generation that is prevalent in today’s microgrids. The INL model is a product of the NZM Program at Idaho National Laboratory.

This article first appeared in Nuclear Engineering International magazine.