DE1065925B - - Google Patents

Description

GERMAN

In the operation of nuclear reactors, especially power reactors, there are malfunctions in which the reactor must be shut down immediately under all circumstances. Such a case exists if, for example, the reactor output continues to increase, for example as a result of an error in the control system. If the reactor output reaches a certain limit value, e.g. B. 43OV0 der normal power, "the emergency shutdown device intervenes and switches off the reactor (scram). For an exact triggering of the shutdown device, the narrowest possible response range is important ) but the response range scatters by at least __ ± __20 _! / <ν -5θ so that the limit value range is correspondingly blurred.

An electronic limit monitor is known,

'in which the pointer of the measuring instrument is provided with a narrow shielding plate, which when reached of the limit value dips between the coupling coils of a transistor oscillator and thus the Coupling interrupted. The oscillator oscillations in the detector stop and a sequence relay triggers the Security mechanism of the monitored device.

Even though the sensitivity of this limit value trigger is great, its response range will be due to the unavoidable finite width of the shielding plate, which is a certain not to be undercut The width of the triggering or tilting range of the electronics is undesirably limited. Of the Limit value triggers can therefore not be used without further ado for tasks in which the individual The size of the control signals assigned to the operational stages differ only slightly from one another, since it then on. a very sharp selective release arrives. These relationships are practically the case in the regulation of nuclear reactors, especially power reactors, in which the power range from 100 to, for example, 130% as the upper Limit value in terms of control technology in several power intervals marked by corresponding electrical signals is divided. The signals assigned to these intervals differ in their nature Size just a little apart. Since the signals preceding the 130% signal have the task of Measures that usually precede the emergency shutdown (advance warning, reversing the control rods etc.), the response range of the limit value trigger assigned to the actual 130% signal must be triggered be very tightly limited in order to prevent false tripping.

The well-known electronic limit value trigger has

Electronic limit value trigger, especially for quick shutdown of nuclear reactors

Applicant: Siemens-Schuckertwerke Corporation, Berlin and Erlangen, Erlangen, Werner-von-Siemens-Str. 50

Herbert Troeger ₁ , Baiersdorf (MFr.), Has been named as the inventor

for the present application still has the disadvantage that it is too sluggish due to its mechanics. These However, inertia cannot be reduced because of the already mentioned finite width of the shielding plate will.

The inertia is also one reason why the known limit value trip unit is not operated with mains frequency can be. In the case of control circuits in nuclear reactors, for safety reasons it is desirable that the network is used to supply and provide a possibly required control signal frequency will. The limit value trigger would then have to have a much larger shielding plate. in the Otherwise, however, this enlargement is practically impossible to achieve.

The invention relates to a limit value trigger which does not have the disadvantages mentioned. Developed fully electronic, its time constant is practically negligible, and it has a narrowly limited one Release area in the sense of the above explanations. For this purpose it contains a Zerierdiode control circuit with a transformer tapped on the primary side with a coupled to it that actuates the triggering means AC voltage circuit. According to the invention, it is characterized in that one each Zener diode is switched on symmetrically to the center tap in the primary circuit of the transformer with common Cathode connection point and that between cathode connection point and center tap a potentiometer and a control DC voltage source are connected.

909 629/229

Claims (3)

The drawing schematically illustrates an exemplary embodiment. In the primary circuit of the transformer 1, symmetrically to the center tap 2, the two zener diodes 3, 4 with a common cathode connection point 5 are switched on Potentiometer 6 and the ionization chamber 7 are connected as a control voltage source. With the help of the transformer 1, the Zener diode control circuit is coupled to the AC voltage circuit 8, which has a generator with a high internal resistance, which in turn works on the input of an AC voltage amplifier A resistor in series with the amplifier input is generated. The actuator circuit 9, 10 belonging to the trigger magnet is connected to the amplifier output. whose value in steady-state operation is greater than that of the dynamic resistance. Changes in the dynamic resistance of the Zener diodes accordingly cause changes in the alternating quantities of the circuit. These changes are the criterion for actuating the trigger, in the case of the reactor for releasing the shut-off rods. It is now assumed that the reverse voltage of the Zener diodes is 3, 4-6 V and that the characteristic curves of the diodes show the sharpest possible kink. The setting of the potentiometer 6 should be made so that a Zener voltage of -5 V is applied to it or to the diodes. The voltage range between - 5 and - 6 V is available for changes to the trigger signal. The amplitude of the alternating voltage is about 2% of the Zener reverse voltage, the frequency 50 Hz. The new limit value trigger then works as follows: In the assumed overload range of the reactor between 100 and about 128%, the alternating voltage coupled into the diode control circuit with the aid of the transformer 1 works up a practically infinite resistance, since the Zener diodes are blocked. The alternating voltage of about 0.12 V is not able to drive the diodes into the Zener knee, i. H. in the tipping point to steer. If the reactor output now increases further to 130% - the pre-warning and preparation stages have already responded - the current delivered by the ionization chamber 7 increases accordingly, and with it the voltage drop at the potentiometer 6. The working point of both diodes moves accordingly towards the Zener knee . As soon as the voltage drop is - 6 V, the tipping point is reached, i.e. H. that the dynamic resistance of the diodes and thus the resistance loading the alternating current circuit 8 collapses. The alternating variables in the circuit 8 now change so that the triggering takes place. The tripping area is thus narrowed to the current interval between the intersection points of the diode characteristic in the kink area with the tripping curves of the disconnection means at the lower and upper limit. Attention should also be drawn to the advantageous mode of operation of the potentiometer in the diode control circuit. Due to its relatively small resistance, the potentiometer converts the current impressed by the ionization chamber into a practically impressed voltage, thus creating the conditions for voltage-dependent control of the diodes. The potentiometer does not have a negative effect on the AC circuit because it is connected symmetrically in the primary circuit of the transformer. The tipping point cannot be spread or blurred. The circuit also has the property that if one Zener diode breaks down (defect) the other diode is short-circuited, and since the potentiometer resistance is small compared to the then parallel input resistance of the AC voltage amplifier, triggering is also effected in such a case. This is in line with the safety principles of a nuclear reactor, according to which both danger signals and faults in the circuit should lead to triggering (scram). The solution according to the invention is expandable. By switching on further direct current control circuits in the supply line between the ionization chamber and the cathode connection point 5 and by connecting corresponding alternating current circuits in parallel, it is possible to set several limit values or a setpoint range. A wide variety of circuit-related operations can then be carried out at the outputs by appropriately interconnecting the trip relays. P A T E N T A N S I 'K (■ C H Ii: 1. Electronic limit value trigger, especially for the rapid shutdown of nuclear reactors, consisting of a Zener diode control circuit, an AC voltage circuit that actuates the triggering means and a transformer coupling the circuits with central tap on the primary side, characterized in that one Zener diode each is symmetrical for center tapping of the transformer is switched on in its primary circuit with common Cathode connection point and that between cathode connection point and center tap Potentiometer and a control DC voltage source is connected. 2. Limit value release according to claim 1, characterized in that the control DC voltage source an ionization chamber is provided. 3. Limit trigger according to claim 1, characterized in that the alternating variables of the AC voltage circuit as a function of the dynamic resistance of the Zener diodes stand and, accordingly, a change in the variables, the actuation of the switching element connected to the AC circuit Consequence. For this 1 "sheet of drawings © 909 629/229 9. »