Ultrasonic High Temperature Sensors - Past Experiments and Prospectives for Future Use

Ultrasonic thermometry sensors (UTS) have been intensively studied in the past to measure temperatures in the range 1800-3100ºC. This sensor type using the temperature dependence of acoustic velocity in materials was developed for experiments in extreme environments. Its major advantages, which are (a) recording capability of a temperature profile deduced from the notches on the sensor rod and (b) measurement near the sensor material melting point can be of great interest when dealing with on-line monitoring of high temperature safety tests or long-term high temperature fuel irradiation experiments. Ultrasonic techniques were successfully applied in several severe accident related experiments under challenging conditions. In the FARO experiments two UTS were used to determine the initial temperature of a UO2 molten fuel prior to delivery of the melt to the test section for studies of fuel-coolant interaction and erosion of stainless steel structures. In PHEBUS FP experiments, two of these robust temperature sensors were embedded in the experimental bundle to measure up to 8 different zones during the whole degradation transient that led to the formation of a pool of molten UO2. For these applications, mainly related to severe accident tests to improve safety of nuclear reactors, these sensors have been successfully applied with an accuracy that has been estimated to +/- 50ºC. For these applications and the targeted range of temperature, tungsten sensor rods had to be used. If some new developments are conducted with other materials, this sensor type may be used in other experimental areas where robustness and compactness are required. Long-term irradiation experiments of nuclear fuel to extremely high burn-ups could benefit from this previous experience. This ultrasonic technology could solve the known problem of massive failures of classical N or K type thermocouples during irradiation tests above 950ºC. These sensors may even be up-graded with adapted fixed point cells located in low neutron flux areas that would enable detection and correction of UTS drift. After an overview of UTS technology, this paper summarizes experimental work performed to improve the reliability of these sensors. The various designs, advantages and drawbacks are outlined and future prospects for long term high temperature irradiation experiments are discussed.

LAURIE Mathias;  MAGALLON Daniel;  PIERRE Jocelyn;  MARQUIE Christophe;  EYMERY Stephane;  MORICE Ronan; 

2011-06-28

University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Metrology and Quality

JRC55178