July-August 2018 NPJ

I&C System Sensors for Advanced Nuclear Reactors By H.M. Hashemian and Edwin Riggsbee, AMS. H.M. Hashemian H.M. “Hash” Hashemian is President and Chief Executive Officer of Analysis and Measurement Services Corporation (AMS); a nuclear engineering consulting firm headquartered in Knoxville, Tennessee, and operating in the United States, Europe, and Asia. His technical and operational vision and leadership have enabled AMS to play a key role in ensuring the safe and cost- efficient operation of virtually every U.S. nuclear power plant, as well as many in Europe and Asia. A globally recognized expert in peaceful applications of nuclear energy for electricity generation and medical diagnostics and treatment, Dr. Hashemian lectures frequently around the world on nuclear power plant instrumentation and control areas. He holds three doctorate degrees in engineering including a Ph.D. in nuclear engineering, a Doctor of Engineering degree in electrical engineering, and a Ph.D. in computer engineering. He has worked for the nuclear, aerospace, and other industries, and U.S. government organizations such as the Nuclear Regulatory Commission, Department of Energy, Air Force, Navy, and the National Aeronautics and Space Administration. Abstract As advanced reactor designers proceed with further research, design implementation, testing, and deployment, it is now time to address their instrumentation and control (I&C) needs. First, we must identify the process variables that must be measured to control an advanced reactor and monitor its safety. As with any nuclear power plant, it is safe to assume that temperature, pressure, flow, level, and neutron flux are the predominant variables to be measured. As a second step, the range of process values must be established as well as the level of accuracy, redundancy, and speed of response of sensors that must be deployed to measure these values. The harsh environments of advanced reactors such as high temperatures, high levels of nuclear ra- diation, potential for corrosion, and lim- ited access to sensors for maintenance are just a few examples of instrumentation challenges. This is compounded by the relatively small mar- ket for new sensors that must be designed, developed, and quali- fied for advanced reactors. That is, the cost of these activities can deter major sen- sor manufacturers from entering the ad- vanced reactor market. Furthermore, the operating cycles of most advanced reac- tors are expected to be much longer than conventional plants adding to the need for instrumentation that can maintain cali- bration and response time over extended intervals. The fact that there are now a variety of advanced reactors under design and development adds to the complexity of instrumentation that may differ for various types of advanced plants. A few examples of the most commonly discussed advanced reactors are reviewed in this paper followed by a brief discussion of their instrumentation needs. Contenders A list of several of the advanced reactors currently contending for development in North America is provided in Table 1. Although there is substantial design work in progress, the time line for deploying these new reactors is tenuous. The reality of commercial operation for advanced nuclear reactors in North America is likely to be around 2030’s time frame. In comparison, development of advanced reactors is closer to realization in China. For example, the construction of the China Fast Reactor 600 (CFR- 600) which is a sodium-cooled plant was announced in January 2018 to be complete by 2023. Ahead of this plant is a high temperature gas-cooled reactor (HTGR), at Shidaowan, a demonstration modular pebble bed reactor in China which loaded fuel in April 2017. These developments show that new reactor deployment is achievable and a good future awaits the arrival of these plants around the world; especially in China, the United States, Europe, and Russia. Technology Overview The basic parameters of some of the advanced reactors are provided in Table 2. As evident by the information presented, advanced reactors can vary significantly with respect to their operating characteristics although all will have high core outlet temperatures, unique primary coolants, significantly longer refueling intervals, and complex geometries that complicate the deployment of conventional I&C sensors. For example, Sodium, unlike water, is a non-moderating coolant and thus allows for a fast neutron spectrum. Shorter neutron lifetime and magnitude of delay coefficient result in a reactor that is dynamically more sensitive than a conventional pressurized water reactor (PWR). Thus, I&C sensors in sodium- cooled reactors must be designed for reliable operation at high temperatures (>500°C), have fast response in order to maintain stable reactor control and timely shutdown, and provide diagnostic capability in case of inadvertent reactivity addition or equipment problems. HTGRs are expected to operate with a low power density compared to PWRs; therefore, the dynamic response and interactions of reactor power and temperature are expected to be slowwhich is good for efficient control and plant 48 NuclearPlantJournal.com Nuclear Plant Journal, July-August 2018