Determination of the sample temperature during irradiation experiments is crucial to the analysis and interpretation of subsequent characterization. Passive thermometry of in-reactor core experiments, through subsequent dilatometry of SiC temperature monitors, suffers from uncertainties that can be as large as ± 50 °C. Optimization of thermometry specimens, to reduce this uncertainty, requires accelerated irradiation testing and reduced sample geometry. However, developments in TM design are hindered by the time and significant cost of instrumented in-core neutron-irradiation campaigns and also by the dimensional requirements of dilatometry specimens. We propose to benchmark ion-irradiation of SiC as a surrogate for neutron-irradiation in order to shrink the required geometry of temperature monitors through nanocalorimetry of ultra-miniature specimens. The proposed work will validate the precise exploration of irradiation temperature of a SiC thermometry piece irradiated in HFIR at nominally 300°C and through well controlled and actively monitored proton and helium ion irradiations at 300°C of SiC. Together, these three conditions will demonstrate the use of nanocalorimetry to conduct passive thermometry at an increased spatial resolution of over 400x compared to current methodologies. This will enable the characterization of temperature gradients within in-core capsules and increase the fidelity with which reactor irradiations can be analyzed and interpreted. In addition, this proposal will establish the use of nanocalorimetry as a technique that can characterize defects that are below the resolution limit of electron microscopy, thus quantifying the most significant contributors to both swelling and degradation of thermal conductivity in irradiated SiC. The proposed work will require one day of ion irradiation and twenty days to produce specimens for nanocalorimetry. The outcome will be an advancement of the fundamental science behind radiation damage in SiC to better understand their limitations as temperature monitors.

The Office of Nuclear Energy (DOE-NE) mission is to advance nuclear energy science and technology to meet U.S. energy, environmental, and economic needs. Silicon carbide (SiC) primarily resides in two aspects of the DOE-NE mission: to develop advanced cladding concepts such as the SiC/SiC composites for accident tolerant fuels (ATF) and to develop advanced passive monitoring sensors. Within the Advanced Sensors and Instrumentation (ASI) cross cutting initiative, research to develop advanced sensors, instrumentation and controls address critical technology gaps for monitoring and controlling existing and advanced reactors and supporting fuel cycle development. As a subset of this program, the I&C Technology Deployment Capabilities Support area focuses R&D activities to characterize previously developed sensors for use in irradiation experiments. These activities include efforts to develop and understand passive peak temperature sensors, both printed melt wire arrays and silicon carbide (SiC) peak temperature monitors. This RTE combines the evaluation of a new measurement technique, nanocalorimetry, compatible with ultra-miniature specimens with accelerated ion irradiations based on the fundamental science of stored energy from radiation damage. Thus, an outcome of this work will be the comparison of properties of proton and helium ion irradiated SiC against widely reported neutron irradiated SiC for the purpose of benchmarking ion irradiation as a viable technique for rapidly advancing the development of materials for advanced reactor concepts. The demonstration of this technique with ultra-miniature specimen volumes will also enable localized property measurements and a methodology to assess heterogeneities from thermal or dose gradients in SiC passive monitors used throughout the community, and microstructural heterogeneities in proposed SiC/SiC composites for LWR ATF applications. While SiC is not a primary focus of the Advanced Materials and Manufacturing Technologies (AMMT) or the Simulating Neutrons with Accelerated Particles (SNAP) programs, this work fits within the spirit of these programs to develop accelerated testing techniques and to address material qualification efforts using combined ion and neutron data.