Patent Number: 059563818
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a preferred embodiment of a first configuration la for detecting the dropping of a control element 3 into a non-illustrated reactor core. Detectors Dl to Dn are disposed in positions X1 to Xn at predetermined distances along a fall path F of the control element 3 (or of a control element group). The number of detectors D1 to Dn and the distances between them depend essentially on the desired detection accuracy and on the acceptable level of expense. For the sake of simplicity, only three detectors D1, D2 and Dn are shown in the figures. The procedure is discussed herein, purely by way of example, with reference to the example of one control element 3. However, it can be applied logically to a plurality of control elements 3 or for all of the control elements 3 of a reactor core. The detectors D1 to Dn can be constructed in a wide variety of ways. They may, for example, respond to radioactivity, heat, electromagnetic effects or other physical effects. It is essential in the present case that the detectors detect the dropping of the respective control element 3 at the place where they are installed, through a physical effect and a corresponding signal. In particular, the following detector types that are known from the art are usable: neutron flux, gamma, beta, alpha detectors and measuring sensors or thermocouples for the local coolant temperature. It is expedient for the detectors D1 to Dn which are in any case disposed in or outside the reactor core, to be used for the present function. They may, for example, be detectors D1 to Dn for determining power density. In the figures, reference symbols S1 to Sn denote signals that are respectively output by the detectors D1 to Dn. When the control element 3 drops downward, the detectors D1 to Dn in each case successively produce the signals S1 to Sn with signal edges, as the control element 3 goes past. The edges (rising edges) of the signals S1 to Sn thus occur one after the other with a time delay. The representation of the signal edges of the signals S1 to Sn which is shown in the figures is chosen according to their time delay on a time axis t (indicated by dashes). In the present case, it is assumed that the detectors D1 to Dn each output a constant signal. The signals S1 to Sn which are shown are therefore, for example, formed as constant signals with rising edges. Other types of signals, for example alternating signals, are likewise conceivable. The signals S1 and S2 are then subsequently delayed, using delay components V1 and V2, in such a way that their edges are approximately simultaneous with the edge of the signal Sn. A relative delay with respect to the signal Sn thus takes place. If n detectors Dn are provided, the detectors D1 to Dn-1 (non-illustrated) have a delay component V1 to Vn-1 (non-illustrated). An adder component 9 is provided, so that a sum signal Sx is obtained which has a large steep rising edge. In order to make the sum signal Sx more readily processable, it may be subsequently further fed through a differentiating component DGS, so as to yield a pulse sum signal Sy which is then fed to a monitoring device 12. The monitoring device 12 is used, for example, for the detection, processing or signaling of faults, or for data transmission and is constructed according to the generally known prior art. It may initiate further reactions to the drop of the control element and is incorporated in a drive or control system of the reactor. The approximate addition of the respective signals S1 to Sn produces a considerable increase in the useful signal component in comparison with the interference signals, which provides better evaluation. Noise components in the interference signal in this case are at least partly eliminated, so that it is easier for the downstream monitoring device 12 to detect the drop. The delay time in the delay components V1, V2 may be fixed in advance according to the sites where the detectors D1 to Dn are installed. The delay times may then be determined by trials or on the basis of theoretical considerations. This procedure can, for example, be carried out by using an analog or digital circuit, in particular a computer. However, the signals S1 to Sn may also be respectively stored firstly. The respective delay time is then given from the difference between the occurrence of the respective signal S1 to Sn and the last signal Sn. This procedure is suitable, in particular, for digital signal processing using a computer. The delay times of the respective delay components V1 to Vn-1 (non-illustrated) can be calculated according to the following relationship: EQU Ti=Xn/v-Xi/v. In this equation, I=1, . . . , n-1: Xi and Xn indicate the positions of the respective detectors D1 and Dn along the fall path F of the control element 3, PA1 Ti indicates the delay times of the respective signals S1 to Sn from the detectors D1 to Dn at the positions Xi and Xn, and PA1 v indicates the fall rate of the respective control element 3. FIG. 2 shows a second variant, in which a configuration 1b has differentiation components DG1 to DGn that are connected downstream of the respective detectors D1 to Dn, in each signal path of the detectors D1 to Dn. The edges of the signals from the detectors D1 to Dn are thereby converted into pulses I1 to In which are well-suited to signal processing. The addition produces a sum pulse Is. A configuration 1c according to FIG. 3 has thresholding components GG1 to GGn connected downstream of the differentiation components DG1 to DGn. In this way, only signals which have a predetermined amplitude are evaluated and delayed. In this case the amplitude is dependent on the dropping rate. A control rod driven slowly into the reactor core therefore does not lead to a detected signal. The embodiment of the configuration lc according to FIG. 3 may also be realized in such a way that the thresholding components GG1 to GGn output binary signals. After the binary signals have been delayed by the delay components V1 and V2, the binary signals are then fed to a coincidence monitoring device 9a. The latter then performs a logical check of the binary signals, through the use of which the dropping of the control element 3 is detected. The coincidence monitoring device 9a then outputs a fault detection signal at its output 10, which is fed to the monitoring device 12 already described above. The embodiment of the configuration 1c is suitable, in particular, for digital signal processing, in which the outputs of the detectors D1 to Dn are connected to inputs of an automation device which has a computer. The signal processing components referred to are then constructed in the form of software or programs. In individual cases, and under certain conditions, a simple detection according to FIG. 4 may also be sufficient. In this case, pulse signals I1 to In are firstly added and then integrated with respect to time using an integrator 15. This produces a sum pulse Is which also leads directly to improved evaluation and detection in comparison with the prior art. This signal may then optionally be subsequently fed to a differentiation stage DS, with the result of providing a characteristic pulse which has a good signal-to-noise ratio. It is also conceivable for the signals to be checked by using logic before they are processed further, in order to detect certain fault situations or in order to stop further processing on the grounds of false information. This type of logical check for the signals is also suitable for an embodiment involving a computer. Any desired combinations of the above-mentioned features are, of course, conceivable within the knowledge of the person skilled in the art, without departing from the fundamental concept of the present invention.