Patent GB-984641-A (GB)
Title: Improvements in devices for detecting breaks in fuel element jackets in a nuclear reactor
Inventor: GRAFTIEAUX JEAN
IPC: G01T7/06
Filed: 1961-05-19
Abstract: 984, 641. Monitoring nuclear reactors. COMMISSARIAT A L'ENERGIE ATOMIQUE. March 19, 1961 [May 20, 1960], No. 18287/61. Heading G6C. A device for determining the proportion of fission products in a gaseous stream comprises a rotatable metallic drum on which fission products may be deposited electrostatically when a postive ion repulsion electrode is energized; the drum comprising a number of areas on which ions may be deposited, one area on which ions are not deposited, and a recessed area for trapping a given volume of gas to be tested; a radio-activity detector disposed opposite the drum at some distance from the ion repulsion electrode; and calculator means operatively connected with the detector for giving, in response to the measurements made by the detector for the respective areas of the drum, the concentration of shortlived fission products in the gas stream, the concentration of long-lived fission products, and the total activity of the gas stream. Referring to Fig. 5 gas to be tested passes through a filter 6 into a delay chamber 17 and then to the space between the ion repulsion electrode 11 and the drum 10. As shown in Fig. 2 the drum 10 has a number of peripheral areas n on which ions may be deposited, a special area y on which ions are not deposited, and a recessed area x for trapping gas. A scintillation detector 12 and its associated photomultiplier 13 are arranged near the periphery of the drum and the drum is surrounded by a gastight casing 10a; carbon dioxide is passed through a duct 8 to the space between the detector 12 and the drum during measurements, except those made on area x, to reduce the effect on the detector of any active gas which may be present. There may be 20 areas on the drum and the detector may be spaced 3 area away from the electrode 11. The drum is rotated of an electric motor 23, Fig. 5, through magnetic coupling 22 and gearing having a ratio 3:20 so that one complete revolution of motor 23 causes a given area of the drum to move from electrode 11 to detector 12 or vice-versa according to the direction of rotation. The shaft of motor 23 carries a cam 24 which opens contact 24a once per revolution, and the shaft of drum 10 carries three cams 18, 19, 20 which open contacts 18y, 19 y-1  and 20 x  respectively when the drum is stopped with area y opposite the detector, with area y-1 (the area preceding area y in order of scanning) opposite the detector, and with area x opposite the detector. These contacts select the appropriate one of relays R x  R y-1  R y  and R x  for for area under examination, and the relays control the programme in conjunction with contacts 35 which are operated by cams of shaft 36 to produce the pulses shown in Fig. 7. At the beginning of an elementary cycle a cam of shaft 36 closes a contact in line KA and sends a pulse ka t relay R E  which opens contact a and cancels the previous programme of de-energizing relays R. Pulse ka also operates relay 39 and causes motor 23 to rotate on revolution (further rotation is prevented by cam 24 and contact 24a) and bring a fresh area of drum 10 opposite detector 12. A pulse kb then actuates one of the relays R which holds itself on by a contact m. If the area is a normal one, relay R n  is energized and the area is moved to the electrode 11 and back again by pulses kd and kf operating relays 39 and 40 respectively. The programme thus comprises three period, a first period before pulse kd for measuring the residual radioactivity N 1  of the area, an ion collecting period when the area is opposite electrode 11 which is energized by pulse ke operating on relay 31, and a period after pulse kf for measuring the radioactivity N 2 . During the programmes for area x and y, these areas remain permanently opposite the detector and the active period is at the end of the cycle, pulse kj, for area x and in the middle of the cycle, pulse ki for area y. Fig. 6 shows the computer circuit. Detector 12 and photomultiplier 13 are followed by amplifiers 14, 43, two amplitude selectors 44a and 44b having different threshold, a frequency divider 46, a wave shaping stage 48, a second frequency divider 46a, two integrator 49a and 49b of different sensitivities and an amplifier 51. The first measurement is of a sealing factor a proportional to neutron flux in the reactor and determined by the activity of gas trapped in area x. While area x is being monitored a pulse w on line WX operates relays 45 and 50 and selects the appropriate amplitude selector 44b and integrator 49b. A pulse kj on line KJ energizes relay 65 which has three effects: current is supplied to winding Q 1  which couples a servomotor 62 to the sliding element of potentiometer P 1 ; the output of amplifier 51 is fed to terminal 63a connected to the input amplifier of servomotor 62 so that the sliding element of P 1  is moved until it indicates the value a (the servomotor operating to produce equal potentials at terminals 63a and 63b); the output of amplifier 51 is fed to the grid of valve 80 (relay 66 being closed) and from there to an output terminal 82b connected through contacts of relay 69 (not energized) to a terminal 85b connected to a seconder (not shown). When monitoring a normal area the output of unit 51 is fed to subtraction unit 52 during the first and third periods through relay 53 operated by pulse kc; relay 54 is operated during the third period by pulse kg, and the difference N 2 -N 1  = F, which represents the activity of short-lived ions, is available on the cathode output of triode 79 at terminal 82a which is connected to the recorder through terminal 85a. Changes in the value of F may be studied by calculating the quantity E = F-a F 0  where F 0  is an initial value of F. If button 59 is pressed at the end of a cycle when relay 60 is energized by a pulse kg on line KG, relay 61 operates and its five contacts produce the following effects: (a) the lamp 75 is switched on (b) Q2 is energized to connect the sliding contact of P 2  to the servomotor 62 (c) relay 70 is energized to couple together valves 79 and 76 (d) the sliding contact of P 2  is connected to contact 63b and (e) the output of unit 52 which is equal to F is connected through valves 79 and 76 to contact 63a and the sliding contact of P 2  is therefore moved until its potential is equal to F. Since a is supplied to P 2  from P 1  the quantity a F 0  is stored in P 2  and is supplied to the grid of valve 80. Since the grid of valve 79 is supplied with F, E can be read from meter 81 and a F 0  can be recorded on the recorder through line 82b. Determination of the ratio P/F of the activities of long-lived and short-lived ions is made from measurements on areas y-1 and y. On area y-1 N 1  and N 2  are stored and subtracted in unit 52 as for a normal area, but in addition N 1  is stored in capacitor 55a through relay 57 operated by a pulse kh in line KH. During the next cycle, which monitors area y, relay 67, which was switched over by a pulse on line WY-1 on the preceding cycle, returns to normal and Ny is stored in capacitor 55b; pulse ki then operates relay 68 and the signal P = N 1  - N y  is connected to the grid of triode 77. Pulse ki also operates relay 69, the contacts of which connect the output of triode 77 to potentiometer P 4  and energize winding Q 34  which causes the sliding contacts of P 3  and. P 4  to be driven together by servomotor 62. The contact of P 3  is connected through relay 69 to terminal 63b and terminal 63a is connected to the outputs of valves 79 and 76 in series and its potential is therefore proportional to F. Thus the resistance of P 4  is adjusted to be proportional to F and the potential applied to it is proportional to P, so the current through it is proportional to P/F and is measured on the dial 83 and transmitted through terminals 84a 84b and relay 69 to the recorder. High values of P/F indicate leaks too small to be detected by measurements of F. Specifications 819,366, 850,308, 899,947, 923,083, 944,049 and 945,304 are referred to.