Abstract
The Advanced Gas Reactor-5/6/7 (AGR-5/6/7) experiment is the fourth and final experiment in the AGR experiment series and will serve as the formal fuel qualification test for the TRISO fuels under development by the U.S. Department of Energy. Certain locations in this experiment reach temperatures higher than any of the previous AGR tests, up to 1500°C. Such extreme temperatures create unique challenges for thermocouple-based temperature measurements. High-temperature platinum-rhodium thermocouples (Types S, R, and B)and tungsten-rhenium thermocouples (Type C) suffer rapiddecalibration due to transmutation of the thermoelements fromneutron absorption. For lower temperature applications, previousexperience with Type K thermocouples in nuclear reactors haveshown that they are affected by neutron irradiation only to alimited extent. Similarly, Type N thermocouples, which are morestable than Type K at high temperatures, are only slightly affectedby neutron fluence. Until recently, the use of these nickel-basedthermocouples was limited when the temperature exceeds 1050°Cdue to drift related to phenomena other than nuclear irradiation.Recognizing the limitations of existing thermometery to measuresuch high temperatures, the sponsor of the AGR-5/6/7 experimentsupported a development and testing program for thermocouplescapable of low drift operation at temperatures above 1100°C. High Temperature Irradiation Resistant Thermocouples (HTIR-TCs)based on molybdenum/niobium thermoelements have been underdevelopment at Idaho National Laboratory (INL) since circa 2004. A step change in accuracy and long-term stability of thisthermocouple type has been achieved as part of the AGR-5/6/7thermometry development program. Additionally, long-termtesting (9000+ hrs) at 1250°C of the Type N thermocouplesutilizing a customized sheath developed at the University ofCambridge has been completed with low drift results. Both theimproved HTIR and the Cambridge Type N thermocouple typeshave been incorporated into the AGR-5/6/7 test, which beganirradiation in February 2018 in INL’s Advanced
Highlights
The Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) is being used to conduct an experiment series designated the Advanced Gas Reactor (AGR) tristructural isotopic (TRISO) fuel experiments to qualify this fuel’s irradiation performance for High Temperature Gas Reactor (HTGR) applications
As with the previous AGR experiments, it consists of multiple capsules stacked vertically and with separate temperature-control gas blends for each capsule
All of the test trains in the AGR experiment series incorporated a similar design
Summary
The Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) is being used to conduct an experiment series designated the Advanced Gas Reactor (AGR) tristructural isotopic (TRISO) fuel experiments to qualify this fuel’s irradiation performance for High Temperature Gas Reactor (HTGR) applications. The use of these nickel-based thermocouples is limited when the temperature exceeds 1050°C due to drift arising from minor alloying elements migrating from the thermocouple’s metal sheath to the thermoelements This change in the composition of the thermolements results in significant decalibration of the signal. Because it was designed as the fuel qualification and margin test, the AGR-5/6/7 experiment requires measurements in locations with higher operating temperatures than any of the previous experiments. Recognizing the limitations of existing thermometry to measure such high temperatures, the AGR-5/6/7 program sponsor supported a development and testing program for thermocouples capable of low-drift operation at temperatures greater than 1100°C. Used hightemperature commercial thermocouples—such as platinumrhodium (Types S, R, and B) and tungsten-rhenium (Type C)—
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