The objective of this project is to perform neutron irradiation damage test on one kind of polymer derived SiAlCN ceramics (PDC). If our hypothesis is correct -- the microstructures and electrical properties are maintained under irradiation -- such material will later be designed as a temperature sensor in nuclear reactor for in-core temperature measurement (It will be the goal for the next phase). In this phase of project, irradiation experiments will be performed at PULSTAR reactor at North Carolina State University (NCSU). Temperature sensors for nuclear reactor applications are subject to high temperature, high pressure, and irradiation challenges. Currently, wired thermocouples are the most common temperature sensor used in nuclear reactors. The current nuclear field has made significant advances in thermocouple design, but there are still limitations in durability and increased expense in instrumented test assemblies. In our previous work, we have been able to demonstrate that SiAlCN materials pertains good semiconducting behaviors and good thermal resistance up to 1050 oC. Both leaded and wireless sensors have been designed and experimented with excellent accuracy for a duration of time (10 hours). Even more appealing, the crystallinity and composition of SiAlCN materials can be adjusted and controlled to modify the electrical conducting properties and sensitivity gauging factor. This proposed work intends to test the irradiation stability of such ceramic sensing materials, and if successful, in the next step, we will design a temperature sensor based on such material for nuclear reactor temperature measurement. Irradiation stability is one of the most important factors to ensure the performance of the PDC sensor material for nuclear application. PDCs are mostly used at non-crystalline state, which makes them less brittle. PDCs also exhibit a more stable structure than crystalline SiC and Si3N4, which is inferred from their higher creep resistance and higher thermal stability. Unlike conventional materials, the PDCs consist of nano-domains created by intertwined graphene (aromatic carbon) sheets about 1-5nm in size. The unique structure of PDCs can effectively promote defect recombination to mitigate radiation damage. During this task, we will assess the irradiation tolerance, microstructural stability and electric properties of PDC material to understand the radiation effects on its sensing capability. In total, it will take six months to perform this research, including (1) sample preparation, (2) material property characterization before irradiation test, (3) perform Irradiation test, (4) material property characterization after irradiation test, data analysis, and material properties comparison, and (5) finishing documentation and research summary. Scanning Electron Microscope (SEM) and Optical Microscopes (OM) will be used to examine the surface of irradiated samples. X-Ray Diffraction (XRD) will be used to investigate the possible irradiation induced crystallinity change in the sample, in which case, further Transmission Electron Microscopy (TEM) investigations will be used. Based on the radiation test results and PIE analysis, further optimization on material composition and fabrication process will be performed to ensure its irradiation stability in such harsh nuclear environment.

Micro-sensors that can measure the fuel temperature in a nuclear reactor under severe conditions are critical for in-situ monitoring of the operating parameters and for accident management. The use of such sensors will enhance reactor safety through early intervention thus minimizing potential accident damage. However, developing robust sensors that can serve this function is not a trivial matter. A major technical challenge in this regard is that the sensors must survive the severe conditions arising during transient and accident conditions both structurally and functionally. These conditions include high temperatures, up to 1500K, solid state corrosion and high levels of radiation damage . These challenges and requirements largely restrict the current sensors from the application, in which case, such sensing materials usually suffer severe structural and functional degradations when exposed to high-temperature irradiation in reactor environment, thus losing their sensing capability.



On another hand, the design times for nuclear fuels are legendary amongst the scientific community. The main culprit for the long design times is the “cooling off period” measured in years that irradiated nuclear fuel must go through before being handled. The fuel sits in a “cooling” pool until the fuel rods can be transferred to a nuclear facility that can perform post irradiation examination (PIE) of the fuel. The transfer process and the hot cell coordination also add months to get to the point of being able to open the fuel cladding to characterize the performance of the fuel. To help speed the design process a series of experiments are planned in advance to “cook” the fuel under various conditions to be “looked” at years later. Thus far, this is the only approach available to the fuel designer. However, unexpected events and transients do occur in the reactor and within the experiment. These unplanned conditions can have unknown consequences on the fuel. It will take the fuel designer nominally 2.5 years to open the fuel cladding and determine what happened and another year to plan and redo the experiment. Thus, it will take a total of 6 years to complete the study or perhaps decide to live without the data.



For such cases, even a simple temperature measurement would be helpful in understanding fuel performance as temperature plays a large role in the lifetime of a fuel assembly. However, the current in-pile temperature sensing technology such as melt wires and silicon carbide bars reside within the fuel cladding and are not accessed until the cladding is cut open 2.5 years later.



To solve this problem, this project is to propose one candidate sensing material one kind of polymer derived SiAlCN ceramics (PDC), and perform neutron irradiation damage test on such material to see how the material properties are affected. If successful, the proposed ceramic sensing material can be applied in light water reactors and other reactor concepts, such as high-temperature gas-cooled reactors. Several other types of sensors, e.g., heat flux sensor, stress sensor, strain sensor, can be designed in the next phase to take measurement inside the cladding.