In July 2013 Westinghouse completed the manufacturing and assembly of two test fuel assemblies for its SMR design (225 MWe per reactor). The fuel design for this LW-SMR is based upon Westinghouse’s Robust Fuel Assembly (RFA) technology used in existing PWRs and for the AP-1000 design. In the past, one of the failure mechanisms of concern for PWR fuel is fretting wear. Since this SMR fuel design

is new, having different axial height and grid locations as compared to other current RFA fuel, the fuel rod vibration characteristics will be unique. Thus, Westinghouse is conducting wear testing to ensure that this design has acceptable fuel rod fretting wear performance. The long-term hydraulic testing is performed in Westinghouse’s Vibration Investigation and Pressure drop Experimental Research (VIPER) test loop at its Columbia Fuel Fabrication Facility in Columbia, South Carolina. The VIPER test loop is designed to hold two full-scale, PWR test assemblies that are placed side-by­side. The maximum operating temperature is 400 °F (204 °C), the maximum pressure is 350 psig (238 MPa), and the peak flow rate is 7000 gpm (442 L/s) [17].

14.3 Future trends

The factors that will determine the ultimate deployment of SMRs, and in particular A-SMRs, will focus on the ability of these concepts to compete economically with large LWRs offering lower costs in terms of both construction and operation, improved performance including conversion efficiencies perhaps with advanced PCS technologies, demonstrated enhancements in safety, and where possible generating less waste. The A-SMRs typically involve innovative designs where new fuels and materials are introduced. Several of these designs are for high-temperature applications. For new non-LWR reactor concepts, the emphasis of future R&D will likely focus on the development, demonstration, and qualification of these new materials and fuels.

R&D for new materials will include the development of materials that will need to be compatible with the several coolant types (liquid metals, gas, and liquid salts) at elevated operating temperatures as well as core structural materials such as graphite for HTGR and FHR applications. Advanced steels will be required for fast reactor concepts. R&D efforts are ongoing in the US as discussed earlier in this chapter on the development and qualification of new materials for advanced reactors including A-SMRs under both the ART and ARC programs at DOE-NE.

Work in the US is expected to continue on further development and qualification of TRISO fuels for use in HTGRs and FHRs as well as fast reactor fuels (oxide and metallic). These new fuels and cladding materials will need to be capable of withstanding irradiation at higher fuel burnup as well.

The demonstration of these new materials and fuels will require both modeling/ simulation and experimental capabilities. Given the significant resources required for new facilities, additional emphasis will be placed on modeling and simulation tools for the integration of reactor physics, thermal hydraulic, and structural mechanics models to evaluate the expected performance of these new concepts. Also, the re­purposing or refurbishing of experimental facilities used in the R&D performed earlier the US will likely be evaluated as options to building new facilities to conduct verification and validation of the models.

Additional R&D will continue in looking at how to integrate digital instrumentation and control (I&C) systems and advanced control architectures to enable integration of control, diagnostics, and decision making for highly automated multi-unit plant operations as well as devising alternate concepts of operation for multi-unit SMR designs. Successfully integrating diagnostics capability into new A-SMR design will assist in providing a sound technical basis for extended operation beyond the initial licensed time frame.

Integrating SMRs in general with renewable electric power sources as hybrid systems as a way to balance power on the electric grid due to the intermittency of power produced by such renewable sources as wind and solar and utilize the excess thermal power from the reactor for process heat applications is garnering more attention today. With some large LWRs being shut down due to economic factors resulting from the lower cost of natural gas and decreased electrical demand, these hybrid systems potentially offer a new application for SMRs in general. To effectively evaluate such systems, R&D will be needed in the way of modeling to understand the interactions and control systems for coupling the renewable and nuclear plants. Also, in these coupled systems the reactor may be used more in a load following manner, which will require R&D for controls based upon process heat application and ensuring the safe operation when cycling the reactor through increasing and decreasing power operations.

As some of these A-SMR concepts mature and evolve as more realistic options for future deployment, one may see two trends emerge. Within the US, the first will be focused on potential industry — government partnerships somewhat different from to the cost-share arrangements between DOE and two of the LW-SMR vendors, m-Power and NuScale. These partnerships are focused on a cost shared arrangement to support a design certification approval from NRC. After having demonstrated to a reasonable degree the favorable attributes of these advanced concepts in terms of economic attractiveness, efficient operations, and enhanced safety via government supported R&D, it will likely be necessary for an industry-government arrangement to support the final demonstration in the form of a test or prototype reactor. Such an arrangement would be more appealing to industry if the government were to identify scenarios for deployment to assist federal agencies including the Department of Defense in meeting clean power goals as established by the current Administration. It is straightforward to identify areas where there is significant power demand by groups of collocated federal agencies. Such a consideration would benefit the government agencies with a dedicated source of reliable power and provide the nuclear industry the opportunity to demonstrate the safe and reliable operation of these advanced concepts for further commercial deployment.

The second emerging trend may involve more cooperation between the US and the international community in the development of new and/or shared use of existing experimental facilities, test loops, and perhaps test reactors. Such arrangements would support the government reaching the state of development described in the preceding paragraph at which point the nuclear industry could be engaged to complete final development. Presently, international cooperation is underway on advanced reactor concepts among some 13 countries under the GIF cooperative effort focusing on some six advanced concepts. The costs to construct and operate such test and experimental facilities may be viewed as prohibitive for any one country to undertake. Other opportunities for international collaboration exist via the International Atomic Energy Agency and the Nuclear Energy Agency with the Organization for Economic Cooperation and Development.