Remote measurement of LMFBR fuel assembly outlet temperature by ultrasonics

The paper outlines work which has been performed as part of a joint R and D programme (UKAEA, NNC and CEGB) to develop a remote method capable of measuring core and breeder subassembly outlet temperatures. The technique depends on measuring the transit time of an ultrasonic pulse across the top of a subassembly and using this to calculate the velocity of sound which in sodium is a linearly decreasing function of temperature over the range of interest. Since the method is very fast (several hundred measurements per second are possible) it can also be used to measure rapid temperature fluctuations, temperature noise, which has been shown to be a promising method of detecting internal overheating in a subassembly at an early stage. (author). 2 refs, 11 diagrams