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Real-time characterization of irradiation facilities improves the utilization of the core capabilities of test nuclear reactors. The ability to observe how the local neutron flux (level and spectrum) changes as control elements and experiments change will fundamentally transform our understanding of the underlying physical phenomena that govern the operation of present and advanced nuclear reactors, ultimately providing valuable information for the nuclear energy industry. The objective of this research was to demonstrate how advanced sensors could be used to significantly reduce the time and cost of experiments, improve our understanding of experimental environments, and enable verification and validation of simulation and modeling methods. This was accomplished by designing and fabricating a dedicated real-time instrument test train for the Advanced Test Reactor Critical (ATR-C) facility. The first year of this project focused on the design and modeling of real-time axial neutron flux monitors, leveraging proven technologies pioneered at the Idaho National Laboratory, to characterize the transient that occurs in the Small-B positions at the Advanced Test Reactor and the Advanced Test Reactor Critical Facility. We found that the flux amplitude in those positions can fluctuate as much as 380% depending on the outer shim control cylinder position. The engineering design of the test fixture and flux monitor instrumentation was the objective of the 2nd project year. New capabilities were established to electrodeposit enriched uranium for fission chamber development at the Idaho National Laboratory and trials were begun to characterize the process. The final year included the fabrication of the test fixture and instruments for Advanced Test Reactor Critical Facility. The fabrication process was delayed by supply chain and personal availability caused by the COVID-19 pandemic. However, we were still able to deliver this unique capability to Advanced Test Reactor Critical Facility that will enable future instrument testing and scientific experiments. [ABSTRACT FROM AUTHOR]

Advancements in nuclear reactor core modeling and computational capability have encouraged further development of in-core neutron sensors. Measurement of the neutron-flux distribution within the reactor core provides a more complete understanding of the operating conditions in the reactor than typical ex-core sensors. Micro-Pocket Fission Detectors have been developed and tested previously but have been limited to singlenode operation and have utilized highly specialized designs. The development of a widely deployable, multi-node Micro-Pocket Fission Detector assembly will enhance nuclear research capabilities. A modular, four-node Micro-Pocket Fission Detector array was designed, fabricated, and tested at Kansas State University. The array was constructed from materials that do not significantly perturb the neutron flux in the reactor core. All four sensor nodes were equally spaced axially in the array to span the fuel-region of the reactor core. The array was filled with neon gas, serving as an ionization medium in the small cavities of the Micro-Pocket Fission Detectors. The modular design of the instrument facilitates the testing and deployment of numerous sensor arrays. The unified design drastically improved device ruggedness and simplified construction from previous designs. Five 8-mm penetrations in the upper grid plate of the Kansas State University TRIGA Mk. II research nuclear reactor were utilized to deploy the array between fuel elements in the core. The Micro-Pocket Fission Detector array was coupled to an electronic support system which has been specially developed to support pulse-mode operation. The Micro-Pocket Fission Detector array composed of four sensors was used to monitor local neutron flux at a constant reactor power of 100 kWth at different axial locations simultaneously. The array was positioned at five different radial locations within the core to emulate the deployment of multiple arrays and develop a 2-dimensional measurement of neutron flux in the reactor core. [ABSTRACT FROM AUTHOR]