July-August 2018 NPJ

(Continued on page 50) safety. However, given the low power densities, low heat conduction from the core to the coolant, and high operating temperatures of HTGRs, variations in heat transfer across the core coupled with high coolant velocities can lead to temperature non-uniformities at the core outlet. It is anticipated that this will lead to challenges in obtaining accurate temperature and flow measurements in these reactors. The primary coolant in molten salt reactors (MSRs) is typically either a fluo- ride or chloride salt compound possess- ing good properties for heat transfer simi- lar to water. However, due to the physi- cal properties of the coolant, MSRs can be operated at temperatures up to about 700°C at atmospheric pressure which is a huge advantage for plant safety and con- trol. Past experience with MSRs is lim- ited to work by the Oak Ridge National Laboratory (ORNL) with the Molten Salt Reactor Experiment (MSRE) of the 1960’s. Activation-based Nitrogen-16 (N-16) flow sensors have been evaluated by AMS and found to be feasible not only for MSRs but also for liquid metal reactors to measure flow and also to infer reactor thermal power. AMS currently provides activation-based flow measure- ment technology for the Comanche Peak Nuclear Power Station in the United States and the Sizewell B Nu- clear Power Plant in the United Kingdom. I&C Sensors for Advanced Reactors In conventional PWRs, thermocouples, resistance temperature detectors (RTDs), and pressure/differential pressure transmitters are used to measure the primary system temperature, pressure, level, and flow. These sensors have a long operating history and their failure modes and degradation mechanisms are well understood. However, they were not designed to withstand prolonged exposure to elevated temperatures, high radiation, Table 1. List of North America Advanced Reactors Under Development. Table 2 – Basic Properties of Various Reactor Types. Nuclear Plant Journal, July-August 2018 NuclearPlantJournal.com 49 Edwin Riggsbee Mr. Edwin Riggsbee is a senior engineer who has worked for Analysis and Measurement Services Corporation (AMS) for more than twenty years in the area of instrumentation and control (I&C) testing in nuclear power plants. He is currently the Principal Investigator for a DOE SBIR, “instrumentation and Control Design for Small Modular Reactors”. In addition, Mr. Riggsbee has performed evaluations of I&C system performance for the Advanced Test Reactor (ATR) at Idaho National Laboratory and the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). This work includes implementing online monitoring technologies at ATR under a DOE funded project to help automate I&C maintenance, increase plant reliability, reduce costs, and contribute to long term operation of the reactor. Mr. Riggsbee contributed to the International Atomic Energy Agency’s (IAEA) Nuclear Energy Series document entitled “Instrumentation and Control Systems for Advanced Small Modular Reactors,” that was published in 2017. Mr. Riggsbee is one of AMS’s experts for analysis, diagnosis, and evaluation of core motion, core power, and flow anomalies using reactor instrumentation signals. He has co-authored advanced diagnostic reports for several nuclear power plants. Furthermore, Mr. Riggsbee has significantly contributed to many of AMS’s major projects and co-authored “Advanced Instrumentation and Maintenance Technologies for Nuclear Power Plants,” which is a report that AMS wrote for the U.S. NRC (NUREG/CR-5501). Prior to joining AMS, he served nearly ten years in the U.S. Navy Nuclear Reactor Control Division where he was directly involved with submarine nuclear reactor instrumentation and control systems.