A tightly coupled integrated system will benefit substantially from demonstration via integrated test facility. Such a facility would allow for both physical and virtual representation of subsystem components, requiring either physical or data linkage between the subsystems. A proposed integral test facility could support component testing, partially integrated system testing, and/or fully integrated system testing including interfacing with the electrical grid.

Significant scaled, non-nuclear, integrated system testing has been conducted for space nuclear power and propulsion systems [28-30], which in some cases are essentially scaled versions of the proposed terrestrial hybrid energy systems. Low — capacity fission-power systems are currently being developed for space application via both computational modeling and experimental efforts. The National Aeronautics and Space Administration (NASA) and the Department of Energy Office of Nuclear Energy (DOE-NE) have adopted a hardware-based approach to system development intended for early identification of challenges to the system design, fabrication, assembly, and operation and to assist in design optimization. To minimize cost and development time, a non-nuclear test approach is used to demonstrate integrated system operation during the system design and development stage, offering opportunity for system reconfiguration without the radiological hazards associated with a fueled system.

For a nuclear hybrid energy system, initial hardware demonstration could similarly integrate a physical reactor simulator that uses electric heaters to mimic the heat generated by nuclear fuel pins. Operation of the reactor simulator would rely on a virtual component derived from system modeling to computationally simulate the neutronic response that would be observed in a fueled system using measured system temperatures as state estimators for the heater control logic. Once all the relevant feedback mechanisms are understood for a particular reactor design, appropriate instrumentation and measurement points can be selected for the non-nuclear test hardware such that the virtual reactivity feedback may be applied appropriately. Other system components could be represented by physical hardware or simulated computationally depending on the stage of facility development, the availability of a specified component or subsystem, or the relative experience with that subsystem that impacts the availability of validated computational models. Integrated system demonstration with hardware-in-the-loop allows the researcher to evaluate integration challenges and to characterize system response time and response characteristics.

‘Virtual’ reactor kinetics applied to the control system architecture can generate significant understanding at a system level, but in a manner that allows for system reconfiguration, control system design and demonstration, operator training, test to failure, etc. without the added complexity and security inherent to a nuclear system.

Successful non-nuclear demonstration of a fully integrated NHES will provide a strong foundation for future build of a nuclear prototype. Several test facilities have been built and operated by potential SMR vendors for specific, focused purposes, including testing to characterize the performance of individual components and materials, to evaluate subsystem thermal-hydraulics and to identify and evaluate integral system effects. In many cases these facilities are designed around a specific reactor concept and are intended for testing of traditional LWR designs, but others may be more generally applicable. Potentially relevant non-nuclear test facilities could include the various non-nuclear test facilities constructed to refine the design of the CAREM (Central Argentina de Elementos Modulares) reactor in Argentina, which began construction of a 25 MWe prototype nuclear unit in February 2014 [31]; Korean Atomic Energy Research Institute (KAERI) has built several facilities to verify and refine the design of the System-integrated Modular Advanced Reactor (SMART) plant [32, 33]; Babcock and Wilcox (B&W) has constructed the Integrated System Test (1ST) facility to verify the mPower reactor design and safety performance in support of NRC licensing activities [34]; and NuScale Power has designed and built a one-third scale, electrically heated prototype facility (the NuScale Integral System Test [NIST] facility) to demonstrate concept viability and stability [35].

Study of the design of these test facilities may offer insight into design of an SMR hybrid energy system test bed. Some of the existing test facilities might be leveraged to benchmark component and subsystem models that could be incorporated in hybrid system simulation. Additional facilities may be necessary to verify the performance or refine the design of specific interface components for hybrid systems, such as fast-switch valves that will be necessary to achieve the desired load-dynamic behavior in a tightly integrated system, and buffer components, such as thermal energy and electrical energy storage technologies. Integral system testing with these components installed can then be conducted to evaluate the subsystem interactions across valves and energy storage devices to verify transient system behavior given both anticipated operational occurrences and transients associated with accident conditions.

13.3 Sources of further information

M. F. Ruth, O. R. Zinaman, M. Antkowiak, R. D. Boardman, R. S. Cherry, and M. D. Bazilian, ‘Nuclear-Renewable Hybrid Energy Systems: Opportunities, Interconnections and Needs,’ Energy Conversion and Management, 78 (2014), 684-694.

W. Phoenix, Personal communications with various nuclear plant engineers, 2011.

AspenTech, Aspen Plus Version 2006 (Build 20.0.3.4127), 2006.

Microsoft Corporation, Microsoft Excel 2007, Version 12.0, Redmond, Washington, 2007.

Acknowledgements

Significant contribution has been made to the topics covered in this chapter by fellow researchers at the Idaho National Laboratory. Contributors include Richard Boardman, Michael McKellar, Richard Wood, Humberto Garcia, Piyush Sabharwall, and Cristian Rabiti. Opinions expressed in this chapter are that of the author and are not attributable to the US Department of Energy or the Idaho National Laboratory.