S. Bragg-Sitton

Idaho National Laboratory, Idaho Falls, ID, USA

Notice: This manuscript has been authored by Battelle Energy Alliance, LLC under Contract No. DE-AC07-05ID14517 with the U. S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

13.1 Introduction

Large-scale nuclear reactors are traditionally operated for a singular purpose: steady- state production of dispatchable baseload electricity that is distributed broadly on the electric grid. While this implementation is key to a sustainable, reliable energy grid, small modular reactors (SMRs) offer new opportunities for increased use of clean nuclear energy for both electric and thermal ap plications in more locations — while still accommodating the desire to support renewable production sources. There are several questions that a potential investor or utility must ask before making the decision to build a power plant, followed by the decision on where to site that plant:

• What is the specific energy requirement that needs to be met? Is it primarily thermal or electrical, or a mix of both? Could a single integrated energy system meet both needs?

• Does the energy demand vary over short or long time frames (e. g. hourly, daily or seasonal)?

• What resources are available in the region (water, land, carbon feedstock, etc.)? Are these resources necessary to the operation of a proposed energy system? Can they be used to enhance the operation of an integrated energy system?

• Is renewable generation an attractive option in the region? Are renewables presently in use (wind, solar, hydro, geothermal, biomass, etc.)?

• Will the proposed power plant be integrated on a small or large electricity grid, or will it be operated independently to support a specific industrial need?

The answers to these and related questions provide the framework for a multi-purpose implementation of nuclear energy systems that could integrate multiple resources to produce multiple output products. Co-generation systems (single input systems,

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.3.319
providing both thermal and electrical output) and multi-input, multi-output nuclear hybrid energy systems (NHESs) can be designed to operate flexibly based on thermal and/or electrical energy demands while accommodating multiple input streams. Those input streams could be several independent reactor units or a combination of resources such as nuclear reactors, windmills, solar panels, biofuels and fossil fuels.

Given the strong public (and, hence, political) desire to support non-carbon-emitting sources, electricity produced by renewable sources is often treated as ‘must-take’ on the grid. This scenario can mean that the baseload provider is required to ramp down production when the wind is blowing or the sun is shining, or sell electricity at a loss. The intermittency of renewable plants, such as wind and solar, occurs on a relatively short timescale. This intermittency places significant demands on the dispatchable, baseload plants that also supply the grid because they are then required to vary relatively large fractions of their load over a short time. A recent report by the Organisation for Economic Co-Operation and Development (OECD) Nuclear Energy Agency (NEA) states that the substantial amount of renewables that have been introduced on the grid in Germany has ‘repeatedly led to prices below the marginal costs of nuclear, including several instances of negative prices’ [1]. These scenarios are not attractive economically, nor does load-following by ramping reactor power up and down look good from the perspective of plant operations and maintenance. In these cases the renewables are connected directly to the grid, resulting in loosely coupled generation sources. This chapter considers an alternate scenario in which renewable generation would be tightly coupled with the nuclear generation source — behind the grid — to meet the grid demand as an integrated energy system while simultaneously producing other commodities with the available thermal energy.

Increasing the penetration of clean, affordable, reliable, secure, and resilient energy sources on electrical grids around the world can be accomplished by progressively establishing tightly coupled systems of distributed, dispatchable power generation assets that include a high penetration of intermittent renewable resources and energy storage or buffering units. Optimization and integration of these more complex and interactive power systems will require new technology with new approaches to deliver the optimized energy services across local, regional and national boundaries. Recent advances in control systems, energy management systems, advanced informatics and forecasting enable innovations in integrated plant design.

G. T. Mays

Oak Ridge National Laboratory, Oak Ridge, TN, USA

Notice: This submission was written by the author acting in his own independent capacity and not on behalf of UT-Battelle, LLC, or its affiliates or successors.

14.1 Introduction

This chapter presents an overview of the research and development (R&D) underway in the US on small modular reactors (SMRs) including all reactor technologies. R&D on SMRs sponsored by the US government is presented first, followed by R&D being conducted by the commercial nuclear power industry on SMRs.

The responsibility for conducting SMR R&D within the US government is that of the US Department of Energy’s Office of Nuclear Energy (DOE-NE). Presently, DOE-NE’s programs include a spectrum of activities spanning support for near-term deployment with emphasis on (1) licensing support to secure design certification approval from the US Nuclear Regulatory Commission (NRC); (2) first-of-a-kind design, engineering, and construction; and (3) generic issues such as source terms, staffing requirements, siting, economics, etc., to longer-term initiatives aimed at developing advanced technologies and conceptual designs for advanced SMRs (A-SMRs) employing coolants other than water.

The SMR R&D highlighted in this chapter being conducted by the nuclear industry is in support of the near-term light-water SMR designs (LW-SMR). Note that the LW-SMR designation used here includes the integral pressurized water-cooled reactor (iPWRs) designs as well as other non-integral SMR designs. Given that these designs are based on well-understood LWR technology, the R&D in support of the LW-SMRs as conducted by the nuclear industry is obviously applied R&D as opposed to longer-term R&D, which is typically the role of the government. More specifically here, the emphasis is on R&D being conducted at any commercial test and/or experimental facilities.

Finally, comments are offered as to the direction and content of future A-SMR R&D in the US as might be indicated by R&D initiatives currently underway.

Please refer to Chapter 2 for additional descriptions of SMR designs under commercial development in the US as well as those under development at various universities and DOE national labs.

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Copyright © 2015 Elsevier Ltd. All rights reserved.

The secondary system receives superheated steam from the NSSS as shown in Figure 15.9. It uses most of the steam for electricity generation, seawater desalination and

Figure 15.9 Schematic diagram of the SMART secondary system.

the pre-heaters. The main steam pressure is controlled so as to be constant during a power operation. A load change is achieved by changing the feedwater flow rate. A seawater desalination system such as the MED (multiple effect distillation), MSF (multiple stage flash), and RO (reverse osmosis) may be used in conjunction with the secondary system by using proper interfacing methods.

Since the iPWR steam generators are integral to the pressure vessel, an area within the vessel must be allocated for upward reactor coolant flow from the fuel assemblies to the upper tube sheet at the top of the integral steam generator(s). This area is often referred to as the riser section. It is analogous to the RCS hot leg in a current large PWR. At the top of the riser section, coolant flow will be directed down into the integral steam generator(s). In addition, the riser section provides space for the control rod drive mechanisms to operate.

Wireless systems are popular in today’s high tech environment, but they will always pose a problem for a nuclear safety system. The concern for wireless safety systems is mostly security. As anyone who works with wireless systems can verify, any system that is wireless is vulnerable. It is vulnerable to jamming, it is vulnerable to hacking, and it is a potential interferer for other signals. Even with encryption techniques and spread spectrum techniques it is unlikely that wireless communication will be implemented for primary signal communications in safety systems.2627

Another constraint arguing against wireless communications in safety systems is channel separation, and safety to non-safety separation. Wireless communication separation is more difficult to prove/ensure than wired communications for keeping signals and channels separated.

Wireless networking and programming of non-safety I&C devices is a different matter. The wireless HART system is a wireless communication system employed currently in large PWR plants, which allows transmitters that are equipped with the system to communicate information to an end user or device. This programming and control system protocol is encrypted and authenticated and has little risk of being hacked or sabotaged. Since it is not responsible for the primary safety communication (for safe plant shutdown), it is free to be used throughout NSSS and BOP control systems. This technology allows plant maintenance personnel to set up, tweak, and network transmitters remotely, and will most likely be used regularly in iPWR systems, for ease of access reasons.28

BOP instrumentation has the most flexibility for wireless communications. Although the wireless solution still has to be tested for signal integrity, immunity, and non­interference with other signals, the potential to use wireless solutions for sensor to processing electronics is greater in BOP systems than in the NSSS or safety system applications.

Wireless voice communications have been widely used in nuclear power plants for many decades. From the handheld radio to cell phones, wireless communications are a continuing trend. As many applications in the new iPWRs will be digital, and digital on a smaller scale than ever before, there will be more intense testing and qualifying of wireless voice communication devices than before. The potential of a wireless voice communication device to interfere with a safety or control signal is a condition that must be fully tested and verified in any nuclear plant environment. The wireless communication of voice or ancillary data is very different from the wireless communication of safety parameter signals. While wireless voice communications are used and will continue to be used in the future, complete testing of these wireless systems will also continue to a necessity for electro-magnetic compatibility (EMC) reasons.

Wireless plant computer data is already a popular technique in power plants. As long as the plant computer data is not relied upon for safety system processing, wireless plant computer data is a solution that benefits everyone. Currently, much diagnostic information, such as vibration data and temperature data, is sensed in the field and transmitted through wireless hubs to a computer system. It is expected that this trend will continue in the iPWR environment.2627

The flip side of the coin in wireless systems is the potential for the wireless transmission to jam or interfere with other systems, both wired and wireless. EMI/ RFI issues, concerns and guidelines for nuclear plants are covered in Electric Power Research Institute (EPRI) report TR-102323-R3 published in November 2004, and EPRI report ID# 1011960 published in 2005.

1.3 Conclusion

iPWRs are a new and elegant incorporation of 50 years of operation in nuclear power plants. Lessons learned and evolutionary improvements are being and have been incorporated into the designs. The instrumentation design, typically the last design detail to fit into the overall design, is in its initial design phase at the current time. Many traditional I&C options are still being considered for iPWRs, but some of these traditional options will not work in the new iPWR designs, either because of the geometries involved or because of the environment. It is up to the iPWR I&C designer to find the appropriate I&C solutions to the problems of pressure, flux, level, temperature, and flow measurement. The opportunity to use state-of-the-art technologies that offer improved accuracy, ease of installation, ease of maintenance, and less drift should not be passed up, even if it means new qualification programs. Economics will bear out the use of new technologies, but only if a long-term view is used. The next ten years should tell the story.

Although the term ‘intelligent’ is perhaps a misnomer in HSIs, it is nevertheless an important development. This is a class of technology that mimics certain aspects of human reasoning and behaviour. Such systems employ statistical and probabilistic methods in conjunction with neural networks, databases, rules and a variety of sensors to approximate human traits of reasoning, knowledge, planning, learning, communication, perception, and the ability to manipulate abstract or concrete objects (Ehlert, 2003). Software systems that are able to perform such functions could be called intelligent software agents. When this forms part of the HSI, such an agent would act in collaboration with the operator, for example, to detect certain patterns of operator responses in his or her use of the HSI, such as the need to perform a calculation. It would then either autonomously perform the function for the operator, or submit the result to the operator for approval. More sophisticated agents equipped with cameras and sensors could even detect stress and workload from the operator’s voice and facial expression and offer to activate specific operator support functions.

Other sensor technologies that are already common in many industries are now also slowly being deployed in the nuclear industry, For example, RFID tags (radio­frequency identification) and GPS (global satellite positioning systems) are being used to locate personnel as well as components in the plant.

To ensure the completeness and adequacy of results, one must structure the problem systematically, assemble an expert analysis team, and ensure competent peer review. The specific steps associated with Activities D and M are described below.

In the US, the NRC, the nuclear industry, and other stakeholders have been collaborating and addressing potential licensing, policy and technical issues for SMR LWR designs since 2009. These issues result mainly from the key differences between the new SMR designs and current large LWR designs (such as size, moderator, coolant/ cooling systems, fuel design, and projected operational parameters). But they also result from proposed review approaches and modifications to current policies and practices. The NRC staff addressed the key licensing and policy issues in SECY — 10-0034 (28 March 2010) and the following provides a brief description of those key issues.

The long-term resiliency and sustainability of a hybrid system are important but difficult attributes to quantify. NHES that can adapt and compete in an evolving market should account for potential future risks and opportunities. This type of predictive analysis, while based on less certain assumptions, is key to making sound investment decisions that will influence future technology implementations.

Classes of risks and opportunities that should be considered include:

• changes in the regulatory framework, with particular attention to environmental protection;

• volatility and long-term availability of raw supplies (fuel, process application feedstock, chemical compounds, etc.);

• reliance of a community or industry on energy generation or chemical production means exposure to supply chain risks; and

• scarcity in the raw material supply or high fluctuation in feedstock prices that subsequently give rise to volatility in the market and ultimately translates to higher overall prices for the final products.

Generally, these situations represent very low probability events, such as scarcity of oil or gas supply, but the consequences of such a shortage could be so dramatic that the overall risk is not negligible.

Portfolio diversification may be important to the long-term sustainability of an energy solution. A hybrid system may offer opportunity for diversification of the current supplier set for the commodities produced by the system. The need for diversification applies to the broad scope of energy commodities, such as providing an economically viable, domestic option for transportation fuels, or more narrowly to diversifying the energy source for electricity production. Diversification is achieved only if the compared energy sources are not correlated. Successful diversification increases the long-term sustainability of the candidate system and may be crucial to the stabilization of long-term energy prices.

In many cases advanced SMRs represent an alternative route to deliver the same products as are currently available (e. g. methanol) by means of different starting materials, contributing to stabilization of the final product by positive diversification.

Low sensitivity of system efficiency to the ultimate heat distribution (end use) offers system versatility, acting as risk mitigation for unforeseen changes in the definition of the system boundary condition (e. g. variation of the demand volume and heat to energy ratio or heat usage).

Hybrid systems naturally diversify customers. For example, if a much cheaper source of electricity is identified by a customer, reducing the electricity demand from the NHES plant, the NHES owner/operator may be capable of adapting production to refocus on heat utilization processes to respond to the demand changes. This operating mode introduces stability in the economic performance and capability to exploit emerging or growing markets.

In June 2013, the DOE announced it intended to provide a total of $3.5m in funding to address certain technical challenges associated with designing, constructing, and operating advanced reactors in the future. Again, as noted in the preceding section, these R&D projects for SFRs and HTGRs would have applicability to A-SMR versions of these types of reactor. The partnerships associated with the $3.5m include a 20 percent private cost share arrangement upon successful negotiation. The following descriptions [13] identify the four responsible organizations and a summary of the scope of the four projects:

• General Atomics — will conduct R&D on silicon carbide composite material, which could act as a safe and reliable material for fuel rod cladding in advanced reactor designs. Better understanding of silicon carbide composite material will help incorporate this material into such designs and support future licensing efforts.

• General Electric Hitachi — will develop high-temperature insulation materials and robust analysis tools to help design and manufacture electromagnetic pumps for liquid metal-cooled reactors. Electromagnetic pumps have fewer moving parts than traditional mechanical pumps, thus improving reliability and safety, while reducing maintenance needs.

• Gen4 Energy — will conduct R&D on natural circulation designs for advanced nuclear reactors that utilize a lead bismuth coolant. The project will develop computer models that will help visualize natural circulation flow and integrate it into safe, reliable reactor designs.

• Westinghouse Electric Company — will conduct analysis on sodium thermal hydraulics to support advanced nuclear reactor design. The project will provide analytical tools to help quantify heat exchanger performance and improve component engineering for sodium — cooled reactor designs.