Neutron sensors capable of real-time measurement of neutrons in high-flux environments are necessary for tests aimed at demonstrating the performance of experimental nuclear reactor fuels and materials in material test reactors (MTRs). In-core Micro-Pocket Fission Detectors (MPFDs) have been studied at Kansas State University for many years. Previous MPFD prototypes were successfully built and tested with promising results. Efforts are now underway to develop advanced MPFDs with radiation-resistant, high-temperature materials capable of withstanding irradiation test conditions in high performance material and test reactors. Stackable MPFDs have been designed, built, and successfully demonstrated as in-core neutron sensors. Advances in the electrodeposition and measurement of neutron reactive material, along with refinements to composition optimization simulations, have enhanced the capabilities of contemporary MPFDs.

Preparation of thin U-and Th-coated 0.3 mm diameter Pt working electrodes by the cyclic potential sweep method is described. Uranyl-and thorium hydroxide layers were electrodeposited from ethanol solutions containing 0.02 M natural uranyl and 0.02 M natural thorium nitrate, each with 3.6 M ammonium nitrate. The cell for electrodeposition was specially developed in order to accommodate the small working electrodes for this research by including a working electrode probe, 3-D translation stage, and microscope. The source material deposition was analyzed using digital microscopy and scanning electron microscopy, and confirmed using x-ray fluorescence measurements. The appropriate potential range for electrodeposition was determined to be-0.62 V to-0.64 V for a 0.3 mm diameter Pt working electrode placed 1 cm from the counter electrode. Smooth, uniform deposition was observed near the central region of the working electrode, while surface cracking and crystalline formations were found near the edge of the working electrode. The final procedure for sample substrate preparation, electrolytic solution preparation and electrodeposition are described.

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General Atomics (TRIGA) research reactor with successful results (Ohmes et al. 2007). However, it was recognized that the manufacturing process was not ideal to produce detectors for in-core applications. The High-Temperature Micro-Pocket Fission Detector (HT MPFD) sensor redesign included several updates from the original MPFD design to improve detector robustness and performance for high-temperature applications. The sensor design was updated from a parallel plate (Unruh et al. 2014) to a parallel wire design (Figure 2). The parallel plate design uses a conductive adhesive that has a potential failure mechanism due to breakdown of the adhesive during a long-duration irradiation test. The parallel wire design does not use this adhesive, eliminating that failure mechanism, which is a significant improvement in HT MPFD survivability.

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