The 6-m long and 90-mm diameter scanner employs a transducer specially developed for immersion in sodium upto a temperature of 250C, which is mounted horizontally at its bottom. The transducer's full movement of complete rotation and 350-mm long vertical travel are controlled by two stepper motors in the drive assembly connected to the top of the scanner. The transducer works on the "pulse-echo" technique.

The scanner was first deployed in FBTR during the year 1988 [1]. It was used as a sweep-arm to scan the space below Core Cover Plate Mechanism (CCPM) of the reactor and was also used to image the CCM. Recently the scanner was deployed in the reactor to scan the interspace between CCPM and Sub-Assembly (S/A) tops for any protruding S/A. The scanning was automated using an IBM- Compatible personal computer. The lower part of the Control Rod Drive Mechanisms in the above interspace was also scanned and their images were displayed on-line. During the program run, the data related to the echo amplitude and range from an ultrasonic inspection instrument (USIP-12) were collected by the PC which was post-processed to yield pseudo three dimensional colour images.

This paper summarises the results of the above deployments and indicates another possible use of the scanner viz. the imaging of S/A tops for measurement of growth' and bowing' which could occur due to certain fast-neutron induced. Also outlined are the efforts under-way to develop a more stable and permanent transducer for use in the scanner. REFERENCES

1. K. Swaminathan, A. Rajendran and G. Elumalai, "The Development and Deployment of an Ultrasonic Under-Sodium Viewing System in the Fast Test Reactor", IEEE Trans. on Nuclear Science, Vol. 37, No. 5, pp. 1571-1577, 1990.