GB1412349A - Radioactive halogen monitoring system - Google Patents

Abstract

1412349 Radio-active halogen measurement GENERAL ELECTRIC CO 13 March 1973 [15 March 1972] 11986/73 Heading G1A A system for detecting radio-active halogen in a sample stream containing other radio-active substances, comprises a plurality of filters each capable of collecting and retaining the halogen and allowing other substances to be flushed away by a purge stream, the filters being subjected in turn to the sample stream during successive collecting periods and to a purge stream during flushing periods following the collecting periods, and the radioactive material collected in each filter being measured during successive monitoring periods which start after the beginning of the flushing period and end no later than the beginning of the next successive collecting period of each filter. As shown, Fig. 1, a gas stream containing radioactive iodine and radio-active krypton or xenon, e.g. from a nuclear reactor, and a purge gas, which may be clean air or steam, are passed alternately through a pair of activated charcoal filters 10(1) and 10(2) by valves 11(1), (2) under control of a timer 18. The filters are provided with separate detectors 13(1), (2) the outputs of which are selected alternately by a switch 14 and applied to a ratemeter 16. The timing cycle is such that the radio-activity of each filter is measured while it is being purged after a short time interval for the removal of noble gases which are not accumulated by the filters. The radio-active iodine is absorbed and accumulated so that the radio-activity measurements increase until an equilibrium between the accumulation of gas and the radioactive decay is reached. The sample gas may be heated before passing to the filters and this assists in the removal of noble gases from the filters. A differentiating circuit may be used in place of or in addition to the ratemeter to indicate the rate of change of the radio-activity. A three filter arrangement is also described, Fig. 5 (not shown), this providing a longer purging interval before the measurement is made. The detectors may utilize Nal crystals.