In-core Measurement Systems for Nuclear Materials Characterization
In-core Measurement Systems for Nuclear Materials Characterization Project Summary
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Engineering topics
Schley, Robert S
Publications and source records attributed to Schley, Robert S.
Demonstrate the Out-of-Pile Performance of a Real-Time Measurement System to Measure Thermal Conductivity Based on Photo Thermal Radiometry
SUMMARY The goal of this project is to develop a fiber-based instrument to perform in-reactor thermal conductivity measurements of fuels and materials. This instrument is based on photothermal radiometry (PTR) and involves heating a sample locally and measuring the induced temperature gradient by collecting blackbody radiation [2]. Thermal conductivity of the sample is extracted by comparing experimental results with a continuum-based model [3,4]. As a laser-based technique, PTR is a non-contact measurement technique that can be performed remotely and non-destructively. In addition, it has several advantages over other photothermal techniques, making it an ideal approach for in-situ measurement of thermal conductivity of nuclear fuels. Because blackbody radiation increases with emissivity and temperature, the PTR technique works well with unprepared surfaces, and measurement accuracy increases with temperature. Moreover, this approach is capable of measuring samples with irregular or poorly defined boundary conditions, which is a common situation for friable spent fuels.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Design of RUSL Irradiation Experiment with Free Standing Sample
During FY19, the MIMIC-RUSL TREAT test successfully measured the shift in resonance of a cantilever beam as it underwent a grain restructuring event in the TREAT reactor core. FY20 efforts focused on a new capsule design which would replace the cantilever beam with a free-free beam. The free-free beam configuration eliminates the cantilever boundary condition and enables internal friction measurements. A test capsule was designed which supported the sample beam at the nodal points of the first flexural vibration mode. Initial tests detected the resonance peak but the signal to noise level was not high enough for in-situ measurements. Several detection probes were tested and a significant increase in the signal to noise was achieved. Although adequate signals and clean resonance peaks were measured when the beam was centered, the beam did not self-center when displaced resulting in distorted and inconsistent resonance peaks. It was concluded that the free-free beam approach is likely not suited for in-situ measurements. Measurement of ZGV plate waves is another option for in-situ microstructure monitoring and should be considered for future work.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
FY20 Status Report on Photothermal Radiometry Development
This report documents FY20 progress in the development of a benchtop photothermal radiometry (PTR) instrument for the measurement of thermal diffusivity. A PTR system incorporating Off-Axis Parabolic (OAP) mirrors was designed and tested. Additionally, a novel analysis technique that accounts for systematic errors that affect measurement accuracy was implemented. Measurements on samples with a range of thermal diffusivities using the PTR setup along with the new analysis technique resulted in improved accuracy and repeatability. Areas for future development work are set forth.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
MESOSCALE THERMAL TRANSPORT MEASUREMENTS OF MULTI-PHASE AND POROUS NUCLEAR FUELS USING A SQUARE-WAVE PULSE THERMOREFLECTANCE TECHNIQUE
The safe and efficient operation of nuclear reactors require accurate knowledge of peak temperatures in the fuel assemblies. The temperature profiles are governed by the thermal transport properties of the fuel, namely the thermal conductivities (k) and thermal diffusivities (D). These values can be very difficult to measure as they are known to vary considerably from the measured bulk values of the fresh fuel, and quickly degrade with increasing burnup [1 -3] . Laser-based techniques have been effectively used for non-destructive and non-contact thermal transport measurements of a wide variety of materials, including nuclear materials [4-6] that would otherwise prove too hazardous or difficult to measure otherwise. In this study, a new thermoreflectance technique known as square-pulse transient thermoreflectance (SPTR) is described and used to determine the mesoscale thermal diffusivity of both uranium sesquisilicide (U3Si2) and uranium nitride (UN) phases in a composite fuel with micron level spatial resolution [7]. This technique employs a rapid train of square-wave pulses from an excitation laser to create a periodic heat flux on a gold coated sample surface. Surface adsorption results in transient film temperatures and hence rapid fluctuations in thermoreflectance that can be measured via a detection laser coupled with a digital oscilloscope. The lasers are coaxially focused on the sample surface, allowing for a sample measurement area of a single convolved laser spot size (~2 µm). A sensitivity analysis was conducted to identify key measurement parameters of this technique using reference materials with a range of thermal conductivities comparable to those of both ceramic, composite, and metal nuclear fuel types (1.4 – 27.2 W/m-K). The reference materials were measured using the new technique as well as a spatial-domain thermoreflectance technique (SDTR) previously reported for a comparison [8]. Additionally, measurements of several U3Si2 and UN phase regions of a polished UN/U3Si2 (70/30 vol.%) sample were taken, and the resulting calculated D values are reported, with both techniques showing excellent agreement between samples. This technique was used to scan a multiphase region at 5 micron increments to generate a local diffusivity map, demonstrating the utility of the techniques for measuring thermal transport properties in specimens with precipitates and secondary phases. Furthermore, the technique is currently being applied to measure thermal properties of Fast Flux Test Reactor (FFTR) irradiated metal fuel specimens whose porous microstructure make it very difficult to measure using other techniques. Comparison of the local scale measurements are compared with the pre-irradiated fuel samples to show the degradation of thermal transport in fuels due to pores from fission gas bubbles and other irradiation induced defects.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗