Patent GB-1472216-A (GB)
Title: Apparatus for monitoring the filling of capsules with a gas containing a radioactive tracer
IPC: G21C17/06
Filed: 1974-07-22
Abstract: 1472216 Gauging by radio-activity COMMISSARIAT A L'ENERGIE ATOMIQUE 22 July 1974 [25 July 1973] 32299/74 Heading G1A Apparatus for checking the filling of capsules with a gas containing a radio-active tracer comprises: a drum for storing the capsules; means for rotating the drum in steps; a scintillator having therein a passage for containing a capsule entirely; means for conveying each capsule in turn from the drum to the scintillator, which is associated with a photo-multiplier; means for comparing the photomultiplier signal with a presettable top threshold and bottom threshold; and means which, when controlled by the photo-multiplier data, convey each capsule to one of three storage positions. A drum 2, Fig. 1, geared to a stepping motor 16 and mounted on a vertical shaft 10 has chambers 4 uniformly spaced at equal radii for carrying capsules (e.g. of stainless steel) filled with gas containing a radio-active tracer,(e.g. krypton 85), suitable for detecting a fracture in a can of fuel elements for a nuclear reactor. As the drum 2 steps round, each chamber 4 is aligned in turn with a fixed duct 26 down which the capsule falls past a detector 29 which may be a photocell, mechanical probe or crystal. When admitted by the withdrawal of a rod 44 actuated by an electromagnet 40 the capsule falls through a duct 30 in a lead tower 28, being halted, by an actuator rod 50, within a passage 38 of a scintillator 34. Apparatus connected to a photo-multiplier 36 counts radio-active pulses emitted by the tracer for a period of 10 or 100 seconds and then signals an actuator 42 to release the capsule into a duct 56. Comparators compare the pulse count with upper and lower thresholds and signal actuators 74, 76 so to position a funnel 68 that, when released by an actuator 60, the capsule either falls straight through the funnel 68 into a compartment 72b for correctlyfilled capsules, or is diverted down the outside of the funnel 68 into a compartment 72a or 72c for respectively over-full or under-full capsules. In a control apparatus, Fig. 2, a relay R 1  controls the drum stepping motor 16. On sensing the transit of a capsule, the detector 29 energises the actuator 40 via a relay R2 to admit the capsule into the scintillator 38 and to trigger a clock H (e.g. a double-mains-frequency pulse generator). A divider D, after measuring out a period of 10 or 100 seconds, operates the actuator 42 via a relay R3 to drop the capsule into the duct 56, Fig. 1. Pulses from the photo-multiplier 36, after amplification at A and shaping at B, are gated at P by the divider D into a counter C associated with a setting-up assembly C<SP>1</SP>. The counter C output is fed to comparators C 1  and C 2  settable to represent upper and lower permissible limits, the result of the comparison being used to control the actuators, 74, 76, Fig. 1, via relays R 5 . With the funnel 68, Fig. 1, thus correctly positioned, the capsule is released by the actuator 60 via a relay R4, and a new pulse is sent to the stepping motor 16. Typically a 95% probability of properly discriminating between correctly and incorrectly filled capsules is attained by setting the limits at 40,000 Œ 400 pulses.