Reliability of high-temperature thermocouples in irradiation capsules

Conference · Wed Jan 01 04:00:00 EST 1969

OSTI ID:4730724

Sandefur, N. L.; Carpenter, F. D.; Grenda, R. J.; Steibel, J. S.

A study of thermocouple behavior and reliability in irradiation capsules was conducted. The investigation covered 16 instrumented (lead-tube type) capsules, which contained a total of 200 Chromel-Alumel and tungsten-rhenium sheath-type thermocouples. The history of each thermocouple was recorded from the time of receipt to insertion in an experiment and during its operating life within the irradiation capsule. Testing conditions ranged from low neutron exposures to a total fluence of 4.5 x 10{sup 21} n/sq cm (E > 0.18 MeV) with operating temperatures to 1800 C. The test data were tabulated into a computer code designed to evaluate thermocouple performance as a function of: (1) neutron exposure; (2) operating temperature; (3) time at temperature; (4) thermocouple type (Chromel-Alumel, tungsten-rhenium); (5) type of hot junction (capped or plugged, grounded, isolated); (6) manufacturer; (7) commercial construction versus construction to Gulf General Atomic specification; and (8) position of thermocouple within the capsule. From these data, correlations were deduced concerning the in-pile behavior of the thermocouples and the probability of their successful operation. Postirradiation continuity and metallographlc analyses were conducted on selected thermocouples to help establish location and/or causes of failure. The computer analyses revealed that a 30% to 40% thermocouple failure rate can be expected under any set of conditions examined. The probability of failure was greater with increasing neutron exposure and longer times in the reactor. Thermocouples purchased to a Gulf General Atomic specification covering materials procurement and thermocouple manufacturing did not perform better than commercial production thermocouples for nuclear service. (auth)

• Research Organization: Gulf General Atomic, Inc., San Diego, CA (United States)
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• DOE Contract Number: AT(04-3)-167
• NSA Number: NSA-24-005967
• OSTI ID: 4730724
• Report Number(s): GA--9653; CONF-690910--7
• Country of Publication: United States
• Language: English

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