July-August 2018 NPJ

NuScale Power Module Instrumentation By Alex Hashemian, Analysis and Measurement Services Corporation and Brian Arnholt, NuScale Power. Alex Hashemian Mr. Alexander Hashemian is a research engineer who currently serves as project manager for a Phase IIB DOE project on process sensors and instrumentation and control (I&C) system design for small modular reactors (SMRs). He has recently served as Project Manager for a Phase I DOE project on evaluating distributed antenna system (DAS) technologies for deployment in existing nuclear power plants. He routinely performs field testing of I&C systems at commercial and research reactors worldwide. Mr. Hashemian has co-authored journal articles and delivered presentations to nuclear industry professionals and universities students on I&C systems in nuclear power plants and sensors for next- generation reactors. Mr. Hashemian graduated Magna Cum Laude from the University of Tennessee with a B.S. in Mechanical Engineering with a focus on Reliability and Maintainability Engineering and an M.S. in Mechanical Engineering with a concentration in heat transfer. His graduate work focused on the development of embedded sensors and numerical analysis methodologies to monitor the condition of thermal protection systems for hypersonic and re-entry vehicles. Introduction The safe and efficient operation of any nuclear power plant (NPP) depends on accurate and timely measurement of the primary system temperature, pressure, level, flow, and neutron flux. Integral pressurized water reactor (iPWR) or small modular reactors (SMRs) present unique challenges to instrumentation and control (I&C) sensors and their maintenance strategies. More specifically, the calibration and response time of these sensors may have to be verified periodically to ensure that they maintain their required degree of accuracy and speed of response. A review of technical reports and safety analysis documentation of the NuScale Power Module (NPM) by Analysis and Measurement Services Corporation (AMS), together with NuScale engineers, confirms that the I&C sensors within the NPM will need to be testable as installed to verify their static and dynamic performance at plant operating conditions. Sensor placement and installation as well as the process conditions expected in natural circulation integral SMRs like the NPM are very different from those in large scale NPPs with conventional primary system loop piping. In particular, reactor coolant system (RCS) flows are more complex and flow rates much lower, the average containment temperature is higher, nuclear radiation levels in some areas are greater, and the accessibility of sensors for hands-on maintenance is very limited. These challenges among others related to I&C sensors can be overcome by adapting existing I&C sensor test methods, developing new techniques for non-conventional I&C sensors, and incorporating online monitoring (OLM) technologies into the I&C architecture of the plant to verify the calibration and response time of sensors within the NPM prior to startup, during operation, and during subsequent refueling outages. These methods and technologies will be demonstrated and validated through a research and development (R&D) grant recently awarded to AMS by the U.S. Department of Energy (DOE) to facilitate timely deployment of the first NuScale SMR in the United States and to enable efficient I&C maintenance strategies during the life of the plant. This paper presents the R&D plan for the DOE project with a focus on temperature measurement needs of NuScale. Sensor Performance Requirements of NuScale In a conventional pressurized water reactor (PWR), the primary system consists of a reactor pressure vessel, pressurizer, steam generators, reactor coolant pumps, and the connecting piping. Making process measurements in a system with piping is straightforward and well-established. In contrast, an iPWR SMR like the NPM has no primary system loop piping, and major primary system components are located inside the reactor pressure vessel within a containment vessel submerged in a large pool of water as illustrated in the simple diagram in Figure 1. This simple illustration shows that a NuScale plant consists of a reactor vessel inside a containment with vacuum in the space between the vessel and the pool. The containment is inside a pool of water that is capped by the bio-shield. The plant design shown in Figure 1 is attractive for several reasons including a more compact containment which can reduce the cost and complexity associated with plant construction and the elimination of the possibility for a large break loss- of-coolant accident (LOCA). However, as a result of this simple and compact design, some sensors will be subjected to higher temperatures and more radiation than conventional PWRs during normal operation and will not be accessible unless the module has been disassembled and moved to a refueling dry dock during an outage. Thus, sensors to be installed in the NPM must be tested before initial criticality and during refueling outages to verify that they have not drifted or suffered response time degradation. This mandate originates from the following statement in Chapter 7: Instrumentation and Controls of the NuScale Final Safety Analysis Report (FSAR) submitted to the U.S. Nuclear Regulatory Commission (NRC): 26 NuclearPlantJournal.com Nuclear Plant Journal, July-August 2018