GB901661A - Improvements relating to apparatus for detecting radio activity in a fluid - Google Patents

Abstract

901,661. Nuclear reactors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 10, 1960 [June 30, 1959], No. 22455/59. Class 39 (4). Apparatus for detecting fission products in the coolant of a nuclear reactor having a coolant in which Cherenkov radiation is produced, comprises means for passing coolant through a sampling circuit provided with a detector for the Cherenkov radiation and means for delaying the flow through the sampling circuit so that the detector is responsive to the longer lived fission products. In a water-cooled reactor the main activity in the coolant is due to nitrogen 16 and it is necessary to delay the coolant for about three minutes to allow the nitrogen 16 to decay before measuring the activity due to fission products. In Fig. 1, the water coolant passes out of the reactor through a duct 4 to a heat exchanger 5 and then back to the reactor. Some of the coolant is passed to an auxiliary circuit through a pump 7, a delay device 8, and a radiation detector 9 including a photo-cell 10 for detecting the Cherenkov radiation. The output of the photo-cell may be fed to a pulse height discriminator, so that only certain fission products are detected. The delay time may be varied, for example by varying the speed of the pump 7, so that different fission products having different half lives may be detected in accordance with the operating conditions of the reactor. Fig. 2 shows one form of detector comprising an elongated casing through which coolant flows from an inlet 13 to an outlet 14 displaced along the casing to ensure good mixing. The casing should be lined with a material which is a good diffuse reflector because of the directional nature of the Cherenkov radiation, and a photomultiplier is located in a casing 15 at one end looking along the length of the casing. In an alternative arrangement, Fig. 3 (not shown) suitable for a pressurized gas system, the casing is spherical and is provided with three photomultipliers at different orientations connected to a common output.