Patent GB-1171389-A (GB)
Title: A method of and apparatus for Differentiating between and Classifying Different Operating Elements contained in the Closed Cycle of a Nuclear Reactor
IPC: G21C17/06
Filed: 1967-02-16
Abstract: 1,171,389. Fuel elements. BROWN BOVERI KRUPP REAKTORBAU G.m.b.H. 16 Feb., 1967 [1 March, 1966], No. 7558/67. Heading G6C. A method of differentiating between and classifying different operating elements contained in the fuelling cycle of a nuclear reactor, such as fuel elements in different states of exhaustion and absorber, graphite, inert and test elements, comprises a first stage consisting in the elements being taken from the reactor core in random sequence and consecutively introduced into a measuring system in which an integrating measurement of all gamma energy groups is performed for determining the dosage energy of the operating elements, followed by a second stage consisting in measuring their neutron absorption for thermal neutrons by conventional neutron detectors, the operating elements being differentiated and classified by reference to characteristic combinations of the measurements performed in both stages. Apparatus for performing this method comprises a shielded casing 1 housing two cylindrical conveying bodies 4, 5 mounted on a common driveshaft 3 which passes through a fixed transferring member 6 with a channel 7 through which an operating element B can pass from a recess 8 in the body 4 to a recess 10 in the body 5. A gamma ray ionization chamber 13 is provided adjacent the body 4, the generated current being amplified by an amplifier 35 and taken to a limit value unit 36. As a source of neutrons, the casing 1 carries a Be block 14 from which neutrons are emitted by Sb-124 embedded at 15 in the block. The neutrons are moderated in a moderator 16 contained in the body 5. The gamma radiation emitted by the operating elements themselves also causes neutrons to be emitted by the Be. Located within range of the neutrons leaving the body 5 are two neutron detectors 17, 18, e.g. BF 3  proportional counters, the neutrons received by the detector 17 having passed through the operating element B. Windows 28, 29, 30 and 31 are provided in a strongly neutron absorbing lining 11. A reflector 33 of a highly hydrogenous material may surround the Be block 14, the moderator 16 and the detectors 17, 18, except in the direction of the neutron flux, to prevent neutron loss. The outputs of the detectors 17, 18 are taken through input amplifiers 19, 20 and main discriminating amplifiers 21, 22 to sealers 23, 24 which register the number of incoming pulses in counters. The sealer 23 is provided with pulse preselector means and after reaching a predetermined number of pulses, e.g. 10<SP>5</SP>, stops the sealer 24 so that the difference in the number of pulses counted by both sealers 23, 24 may be taken as a measure of the neutron absorption of the operating element B in the body 5. The measurements performed by the ionization chamber 13 distinguish test and graphite elements from fuel elements, whereas the neutron absorption measurements in the next stage in combination with the preceding measurements permit graphite and absorber elements to be distinguished and, in the case of a fuel element, its degree of exhaustion to be determined. The counter of the sealer 24 is preferably coupled with limit value comparators 25 which, according to the preselected limiting values, deliver signals signifying different degrees of exhaustion to indicating means when different pulse numbers appear.