TY - JOUR
T1 - Influence of Microstructure and Phase Morphology on the Stability of High Temperature Irradiation Resistant Thermocouples
AU - Riley, Scott
AU - Holloway, Kyle
AU - Bateman, Allyssa
AU - Skifton, Richard
AU - Jaques, Brian J.
N1 - Riley, Scott; Holloway, Kyle; Bateman, Allyssa; Skifton, Richard; and Jaques, Brian J. (2023). "Influence of Microstructure and Phase Morphology on the Stability of High Temperature Irradiation Resistant Thermocouples". Materials Today Communications, 35, 105972. https://doi.org/10.1016/j.mtcomm.2023.105972
PY - 2023/6/1
Y1 - 2023/6/1
N2 - Development of in-core instrumentation is driven by the pursuit of safer and more economic energy production from both existing nuclear reactors and Generation IV reactor designs. Idaho National Laboratory (INL) has developed high temperature irradiation resistant thermocouples (HTIR-TCs) for temperature sensing inside Generation IV nuclear reactors. These thermocouples are composed of phosphorus-doped niobium (Nb-P) and lanthana-doped molybdenum (Mo-LaO) thermoelements, an alumina (Al 2 O 3 ) insulation, and a niobium sheath. HTIR-TCs require an initial heat treatment exceeding the maximum service temperature to stabilize the generated electromotive force (EMF) signal; however, the mechanism behind this stabilization is not well understood. This work evaluates the impact of the stabilization heat treatment on the thermoelements' microstructures, chemical stability, and electrical properties to determine the mechanisms by which the EMF signal stabilization occurs. Accordingly, during the preliminary heat treatment, a secondary Nb 3 P phase formed within the Nb-P, along with an interaction region at the Al 2 O 3 /niobium interface. The formation of secondary phases within the niobium leg of the thermocouple causes an increase in the Seebeck coefficient. Stabilization of the HTIR-TC EMF signal was found to be dependent upon both the equilibrium of a diffusion interaction region at the Nb-P/Al 2 O 3 interface and the formation of Nb 3 P precipitates.
AB - Development of in-core instrumentation is driven by the pursuit of safer and more economic energy production from both existing nuclear reactors and Generation IV reactor designs. Idaho National Laboratory (INL) has developed high temperature irradiation resistant thermocouples (HTIR-TCs) for temperature sensing inside Generation IV nuclear reactors. These thermocouples are composed of phosphorus-doped niobium (Nb-P) and lanthana-doped molybdenum (Mo-LaO) thermoelements, an alumina (Al 2 O 3 ) insulation, and a niobium sheath. HTIR-TCs require an initial heat treatment exceeding the maximum service temperature to stabilize the generated electromotive force (EMF) signal; however, the mechanism behind this stabilization is not well understood. This work evaluates the impact of the stabilization heat treatment on the thermoelements' microstructures, chemical stability, and electrical properties to determine the mechanisms by which the EMF signal stabilization occurs. Accordingly, during the preliminary heat treatment, a secondary Nb 3 P phase formed within the Nb-P, along with an interaction region at the Al 2 O 3 /niobium interface. The formation of secondary phases within the niobium leg of the thermocouple causes an increase in the Seebeck coefficient. Stabilization of the HTIR-TC EMF signal was found to be dependent upon both the equilibrium of a diffusion interaction region at the Nb-P/Al 2 O 3 interface and the formation of Nb 3 P precipitates.
KW - differential scanning calorimetry
KW - electron backscatter diffraction
KW - high temperature irradiation resistant thermocouple
KW - seebeck coefficient; resistivity
KW - thermoelectric drift
KW - Seebeck coefficient, resistivity
UR - https://scholarworks.boisestate.edu/mse_facpubs/568
UR - https://doi.org/10.1016/j.mtcomm.2023.105972
UR - http://www.scopus.com/inward/record.url?scp=85152144045&partnerID=8YFLogxK
U2 - 10.1016/j.mtcomm.2023.105972
DO - 10.1016/j.mtcomm.2023.105972
M3 - Article
VL - 35
JO - Materials Today Communications
JF - Materials Today Communications
M1 - 105972
ER -