Summary of thermocouple performance during advanced gas reactor fuel irradiation experiments in the advanced test reactor and out-of-pile thermocouple testing in support of such experiments

Abstract

High temperature gas reactor experiments create unique challenges for thermocouple-based temperature measurements. As a result of the interaction with neutrons, the thermoelements of the thermocouples undergo transmutation, which produces a time-dependent change in composition and, as a consequence, a time-dependent drift of the thermocouple signal. This drift is particularly severe for high temperature platinumrhodium thermocouples (Types S, R, and B) and tungstenrhenium thermocouples (Type C). For lower temperature applications, previous experiences with Type K thermocouples in nuclear reactors have shown that they are affected by neutron irradiation only to a limited extent. Similarly, Type N thermocouples are expected to be only slightly affected by neutron fluence. Currently, the use of these nickel-based thermocouples is limited when the temperature exceeds 1000°C due to drift related to phenomena other than nuclear irradiation. High rates of open-circuit failure are also typical. Over the past 10 years, three long-term Advanced Gas Reactor experiments have been conducted with measured temperatures ranging from 700°C-1200°C. A variety of standard Type N and specialty thermocouple designs have been used in these experiments with mixed results. A brief summary of thermocouple performance in these experiments is provided. Most recently, out-of-pile testing has been conducted on a variety of Type N thermocouple designs at the following (nominal) temperatures and durations: 1150°C and 1200°C for 2,000 hours at each temperature, followed by 200 hours at 1250°C and 200 hours at 1300°C. The standard Type N design utilizes high purity, crushed MgO insulation and an Inconel 600 sheath. Several variations on the standard Type N design were tested, including a Haynes 214 alloy sheath, spinel (MgAl 2 O 4 ) insulation instead of MgO, a customized sheath developed at the University of Cambridge, and finally a loose assembly thermocouple with hard-fired alumina insulation and a molybdenum sheath. The most current version of the High Temperature Irradiation Resistant Thermocouple, based on molybdenum/niobium alloys and developed at Idaho National Laboratory, was also tested.

Low drift type N thermocouples in out-of-pile advanced gas reactor mock-up test: Metallurgical analysis

“…2 [17]: the total drift for the new thermocouple is +38 μV (about +1°C) after 300 h, whilst for Inconel 600 sheathed type N thermocouple the drift is -307 μV (about -8.5°C). to run trials on them as part of an out-of-pile test to be undertaken in 2014 at INL in comparison with other commercial and customized thermocouples [14]. The INL out-of-pile test was undertaken in Ultra High Purity (UHP) argon at a flow rate of 250 cc/min: the argon was filtered through a moisture/oxygen cleanup cartridge before entering the furnace.…”

“…The thermocouples under test were embedded in a graphite block at the centre of the furnace and supported by graphite spiders, as shown in [14]. A Nb-1%Zr sleeve was used between the Cambridge type N thermocouples and the graphite.…”

“…During the long term out-of-pile test undertaken at INL in 2014 [14] type N thermocouples using a customized sheath developed at the University of Cambridge [17], herein called Cambridge type N thermocouples, were tested along several other commercial and customized type N thermocouples.…”

“…Two long terms out-of-pile drift tests on thermocouples were undertaken at Idaho National Laboratory (INL) in 2005 [9] and 2014 [14]: the tests were aimed at appreciating the drift of several thermocouples before the fuel irradiation campaigns AGR-1 [15], AGR-2, AGR-3/4 [16] and AGR-5/6/7 for High Temperature Gas Reactor applications. During the long term out-of-pile test undertaken at INL in 2014 [14] type N thermocouples using a customized sheath developed at the University of Cambridge [17], herein called Cambridge type N thermocouples, were tested along several other commercial and customized type N thermocouples.…”

Nuclear instrumentation and measurement: a review based on the ANIMMA conferences

“…Further on, a test campaign carried out out-of-pile at Idaho National Lab. (INL) [112] has shown the superiority of the performance of the Cambridge design with respect to the standard construction of type N thermocouples: after 2060 h at 1157°C, the special sheath Cambridge thermocouples had drifted an average of only 4°C, and after an additional 2000 h at 1207°C, the total drift was about 15°C. The metallurgical analysis presented in [113] shows that, at 1300°C, Cr and Fe and also Mn and Al are transferred from the Inconel sheath to the Nicrosil and Nisil thermoelements, while the Cr contamination to Nisil (the most responsible for the drift) is much reduced with the Cambridge special sheath, and the Fe and Mn contaminations to Nisil have disappeared.…”