RU2190264C2 - Actuating element of nuclear reactor control and protection system - Google Patents

Abstract

FIELD: nuclear reactor safety equipment. SUBSTANCE: actuating element has vertically mounted dry can with central and peripheral sleeves, neutron absorbers in peripheral sleeve, and means for holding absorbers in position above the core and driving them into core and resetting to initial position; novelty is that it is provided in addition with ionizing radiation sensor designed for remote control of its entrance in and exit from the core. Means for holding absorbers in upper position are made in the form of assembly of remote-control pawls for absorber hangers and means for lifting absorber from lower to upper position are formed by sensor movable within central sleeve, its lower nozzle being designed for engaging absorber pushing pistons mounted in peripheral sleeves through coupling collet when absorbers are in lower position and for disengaging them when they are in their upper position; piston-to-collet coupling members are disposed in vertical slits between peripheral and central sleeves. Means for holding absorbers in upper position may be made in the form of controlled electromagnet with poles for holding off-line magnetic-control pushing pistons disposed in peripheral sleeves and used as absorber supports; means for lifting absorbers from lower to upper position are made in the form of pneumatic drive formed by same pushing pistons and peripheral sleeves; lower part of each sleeve is joined through central sleeve with controlled-pressure gas line and upper one, with low-pressure (atmospheric-pressure) line. Reactivity control of reactor both during its operation and upon shutdown is effected by means of emergency control signal in response to which absorbers are dropped in core. Energy release of reactor is mainly checked upon reactor shutdown by sending ionizing radiation sensor signal into core and measuring it. EFFECT: provision for integrating reactivity control and energy release check-up functions. 3 cl, 2 dwg

Description

 The invention relates to the executive bodies of control systems and protection (CPS) of nuclear reactors. The intended field of application is the means of high-speed emergency protection (BAS) of RBMK reactors.

 The logic of the work of the executive bodies of the CPS of the BAZ group is as follows: in the absence of emergency deviations of the controlled parameters, the controlled neutron absorbers are located outside the core; when an alarm occurs, the absorbers of the said executive bodies are introduced into the active zone with the maximum possible speed (at the same time absorbers of other executive bodies of the CPS are also introduced into the active zone); almost immediately after shutting down the reactor, the absorbers of the executive bodies of the BAZ group are removed from the core (the reactor remains in a subcritical state).

 Known executive body CPS [1], containing in a vertically mounted dry case a multi-link neutron absorber rod that is moved in height using a flexible traction by a servo drive. The cooling of the case in the channel of the reactor control system is carried out by water flowing through a thin annular gap between the inner surface of the channel and the external case. The cooling of the rod is carried out mainly due to thermal radiation to the inner surface of the walls of the pencil case, partly due to convection of the gaseous medium (air) in the pencil case and heat exchange through the points of contact of the "rod-pencil case".

 The advantage of such an executive body is to ensure a minimum amount of cooling water within the reactor core, or rather a minimum of undesirable input of positive reactivity with possible dehydration of the cooling circuit of the CPS channels. In addition, in the air of the pencil case, it is possible to achieve a high input rate into the active zone of the absorber rod, which is especially important for the executive bodies of the control system of the BAZ group.

 The disadvantage of the described executive body is the single-purpose application: only for controlling the reactivity (power) of the reactor.

 The executive body of the CPS [2], taken as a prototype of the invention, contains a vertically mounted dry pencil case with central and peripheral sleeves, rod neutron absorbers in peripheral sleeves and means for holding the absorbers in a position above the core, entering it and bringing it to its original position. The aforementioned means are made in the form of a suspension moved by a servo-drive uniting the absorber rods into a bundle (cluster). The central sleeve of the pencil case is used to place the elements of the suspension and the so-called displacer-moderator, which slightly increases the efficiency of the absorbers. The suspension is connected to the absorber rods through vertical slots between the central and peripheral sleeves. The cooling of the elements of the executive body is carried out similarly to the above.

 Note that the central sleeve of the pencil case of the executive body at the source [2] also contains the so-called displacer-moderator, which slightly increases the efficiency of the absorbers. However, in other known versions of such an executive body, a displacer-moderator (due to the relatively small effect on the efficiency of absorbers with a significant complication of the design as a whole) is not installed in the central sleeve (see, for example, [2], Fig. 17a) and is accepted in the following statement absent.

 The advantage of the prototype executive body (in addition to the advantages of the analogue according to [1]) is the significantly lower weight of the moving parts (as a result, a significantly lower load on the servo drive) and improved cooling conditions for the absorbers.

 The disadvantage of the executive body of the prototype is the need to manufacture neutron absorbers from relatively more scarce materials (to ensure the absorption capacity of a cluster of rods of small diameter not lower than that of one rod of large diameter). But in this case, it is more important that the prototype executive body, like the analogue of [1], can also be used only to control the reactivity (power) of the reactor.

 The objective of the invention is to expand the functionality of the executive body of the prototype.

 The technical result achieved by using the invention consists in combining two functions in a single design: reactivity control and energy release control in the active zone of a predominantly subcritical reactor. (The emphasis on making it possible to control precisely a subcritical reactor is explained by the fact that the need for tools for such control, which is much more difficult to implement than controlling the energy release in the reactor core when operating at power, is usually more relevant).

 The claimed technical result is achieved by the fact that the executive body of the prototype is supplemented by a sensor of ionizing radiation with the possibility of remotely controlled input into the active zone - output from it.

 The control function in the proposed device is implemented by introducing absorbers into the active zone according to the reactor emergency protection signal when it is operating both in the energy mode and after shutdown, and the control function by entering the active zone and measuring the signal from the ionizing radiation sensor after the reactor is stopped and platoon "absorbers in the upper position (the reactor remains in a subcritical state). The output of the sensor beyond the core, necessary to prevent the burning of its current-forming electrodes with increased sensitivity to neutrons, is carried out after the reactor reaches a critical state with a new (next) rise in power.

 In one of the variants of the proposed device described below, the claimed technical result is achieved in that the means for holding the absorbers in the upper position are made in the form of an assembly of remote-controlled latches for the suspension of the absorbers, and the means for lifting the absorbers from the lower position to the upper are formed by a sensor moving in the central sleeve, the lower shank of which is adapted to engage through the collet of communication with the piston-pushers of absorbers located in the peripheral sleeves in their lower position and uncoupling - in the upper, and the elements of the relationship of the pistons with a collet are placed in vertical slots between the peripheral and central sleeves.

 In another described embodiment of the proposed device, the claimed technical result is achieved in that the means for holding the absorbers in the upper position are made in the form of a controlled electromagnet with poles for holding autonomous magnetic conductor pistons-pushers located in peripheral sleeves and which are the supports of the absorbers, and means for lifting the absorbers from the lower to the upper position are made in the form of a pneumatic drive formed by the same piston-pushers and peripheral sleeves, the lower part five each of which is connected via a central sleeve with a controlled pressure gas manifold, and the top - the backbone low (atmospheric) pressure.

 As you can see, the basis of these designs is the idea of realizing the maximum possible shift of the elements providing the movement of absorbers to the periphery of the pencil case so that the central sleeve of the pencil case is released to accommodate the movable sensor.

 The invention is illustrated by the sketches of the executive body of the control system of the BAZ group of the RBMK type reactor shown in Figs. 1 and 2, respectively, with rod and ball neutron absorbers and fixed sensor communication cables with secondary equipment (the possibility of implementing sensors with mobile communication cables in the form of spiral springs after the above below will become apparent).

 Elements common to FIGS. 1, 2 are: 1 — CPS channel with a flange 2 for supplying cooling water and fastening to the reactor metal structures (not shown); 3 - dry pencil case of the executive body with peripheral sleeves 4, the central sleeve 5 and the flange 6 for connection with the flange 2 of the channel 1; 7 - neutron absorbers; 8 - piston-pushers of absorbers; 9 - supporting dampers to mitigate the shock load on structural elements when dumping absorbers from an upper position to a lower one; 10 - sensor of ionizing radiation; 11, 12 - upper and lower shanks of the sensor; 13a, 13b — elements of a connector for connecting (after entering into the active zone) a sensor to a cable 14 for communication with secondary measuring equipment (not shown); 15 - flexible suspension of the sensor to the drum 16 of the servo 17; the reactor core is highlighted by hatching.

 Additionally, in FIG. 1 is indicated: 18 - electromagnetic latches holding the absorbent rods 7 by the heads 19 of the suspensions 20 with the hinges 21 in the upper position; 22 - collet for coupling the piston-pushers 8 with the head of the lower shank 12 of the sensor 10 (the elements of the relationship of the piston-pushers with the collet pass through the vertical slots 23 between the peripheral and central sleeves of the pencil case 3); 24 - jumper of the central sleeve 5, in which part 10 of the sensor connector 10 is integrated for connection to the cable 14 (connector part 13 a is built into the sensor shank 11); 25 - protrusions of the shank 11 for the azimuthal orientation of the sensor to ensure mutual coincidence of the parts of the connector 13A, 13b.

 Additionally, figure 2 indicates: 26 - connection pipe of the Central sleeve of the pencil case 3 with a gas line of controlled pressure (it is assumed to use a weakly activated by neutrons gas, such as atmospheric air); 27 - holes between the lower sections of the peripheral and central sleeves for supplying high pressure gas under the piston-pushers 8; 28 - connection pipe of the upper ends of the peripheral sleeves with a gas low pressure pipe; 29 - winding of an electromagnet with a pair of poles 30, 31 to hold the magnetically conductive piston pushers 8 in the upper position corresponding to the upper position of the absorbers (power cable of the winding 29 is not shown); 32 - the body of the electromagnet; 33 - radial protrusions in the shanks 11, 12 of the sensor for its azimuthal orientation in the guide tube 34 with the longitudinal grooves 35 to ensure mutual compatibility of the parts 13a, 13b of the connector for connecting to the cable 14 (parts 13a, 13b are integrated respectively in the shank 12 and in the lower part of the tube 34).

 It is assumed that the executive body of the control system in figure 1, 2 also contains elements (not shown) that provide the ability to indicate the position of the absorbers, pistons, pushers and movable sensors.

 In the initial state of the executive body of FIG. 1 (the reactor is at power), the neutron absorbers 7 and the sensor 10 are located above the active zone, and the pusher pistons 8, which are supported by dampers 9, are below it.

 With the appearance of a signal for an emergency shutdown of the reactor, the electromagnetic latches 18 are de-energized and cease to hold the heads 19 of the suspensions 20 of the rod absorbers; there is a “reset” of these absorbers under the influence of their own weight into the active zone to the lower position, followed by support on the piston-pushers 8 and dampers 9. Since at the same time (in accordance with the logic of the CPS), all other CPS absorbers are introduced into the active zone, the reactor goes into a subcritical state (stops).

 In accordance with the previously described logic of the operation of the BAZ means, the absorbers of the considered executive body are again removed from the core after the reactor is shut down. It happens as follows. At the command of the operator, the drum 16 of the servo drive 17 is rotated to extend the suspension 15 and the sensor 10 is lowered to the lower position, in which the head of the shank 11 rests on the jumper 24 of the central sleeve, part 13a, 13b of the connector for connecting the sensor to the cable 14 for communication with the secondary equipment mutually connected, and the head of the shank 12, passing through the collet 22, is slightly lower than it. The spring-loaded petals of the collet 22 are made so that the force required for the shank 12 to pass through them when moving down is less than the weight of the sensor 10 with shanks 11, 12, and when moving up, it is more than the weight of all absorbers 7 and their suspensions 20. Therefore, after formation not only the sensor 10 with the elements 11, 12, 13a, but also the collet 22, the push rods 8, the absorbers 7 and the suspensions 20. The movement of the above elements continues to the level at which the command signal of the operator to rotate the drum 16 in the opposite direction begins holo Ki 19 suspensions 20 are engaged with electromagnetic latches 18, and the collet 22 is in contact with the jumper 24. Traction forces from the drum 16 (servo drive 17) to further advance the sensor 10 upward lead to a stepwise increase in the pressure of the jumper 24 on the collet 22, slipping the head of the shank 12 through the petals of this collet and reset the latter to the lower position.

 After the absorbers return to the upper position, a command signal is generated again to move the sensor 10 downward, as a result of which the shank 11 of this sensor rests on the jumper 24, the parts for connecting to the cable 14 of the connector 13a, 13b are mutually connected, and the head of the shank 12 is lower than the collet 22 The indicated state of the elements, in which the signals of the sensor 10 remain proportional to the height-dependent energy release in the core, is maintained until the reactor is brought to power, usually not higher than 1% of the nominal.

 The procedure for removing the sensor 10 from the core to prevent intense burning of current-forming electrodes of increased sensitivity to neutrons is similar to that described above, with the only difference being that the push pistons 8 with collet 22 move upward until the latter contacts jumper 24 without absorbers 7 and suspensions 20. Traction forces from the side of the drum 16 (servo drive 17) to further advance the sensor 10 up again, they again lead to a stepwise increase in the pressure of the jumper 24 on the collet 22, slipping the head of the shank 12 through petals of this collet and reset the latter to the lower position. The device is again in its original position.

 A characteristic feature of the executive body in the embodiment of FIG. 2 is the complete independence of the sensor controls from the sink controls. The control of the sensor 10 is reduced to moving it to the lower position until the elements 13a, 13b of the connector are articulated for connecting to the cable 14 after the reactor is stopped and to return to its original position after the reactor is brought to power no more than 1% of the nominal. The control of the absorbers 7 is as follows.

 In the initial state of the actuator, the electromagnet coil 29 is under current (voltage) and the pusher pistons 8, supporting the absorber posts 7 from below, are held between the pair of magnetic poles 30, 31 in the upper position (above the active zone), the gas pressure supplied to the nozzles 26 , 28, equally low.

 With the appearance of a signal for an emergency shutdown of the reactor, the electromagnet winding 29 is de-energized and the pusher-pistons 8 together with the absorbers 7 are dumped into the active zone to the lower position with the help of their own weight and then supported by the dampers 9. At the same time, all other absorbers of the control , the reactor goes into a subcritical state.

 After shutting down the reactor at the command of the operator, high pressure gas is supplied to the pipe 26, which, passing through the central sleeve 5, openings 27, the sleeve 4 and the pipe 28 to the low pressure pipe, carries the pusher pistons 8 with absorbers 7 to their initial (upper) position . After applying current (voltage) to the electromagnet winding 29 and subsequent reduction of the gas pressure in the nozzle 26 to the initial (low) piston pushers 8 are held between a pair of magnetic poles 30, 31, and the absorbers 7 are outside the active zone.

Sources of information
1. Emelyanov I.Ya. et al. Design of nuclear reactors. - M.: Energoizdat, 1982, p. 199-200.

 2. Ionaitis R.R. Unconventional controls for nuclear reactors. - M.: Publishing house of MSTU. N.E.Bauman, 1992, p. 63-66, fig.17d.

Claims (3)

 1. The executive body of the control and protection system of a nuclear reactor, comprising a vertically mounted dry case with central and peripheral sleeves, neutron absorbers in the peripheral sleeves and means for holding the absorbers in a position above the core, entering and bringing it to its original position, characterized in which is supplemented by a sensor of ionizing radiation with the possibility of remotely controlled input into the core - output from it.  2. The executive body according to claim 1, characterized in that the means for holding the absorbers in the upper position are made in the form of an assembly of remote-controlled latches of the suspensions of the absorbers, and the means for lifting the absorbers from the lower position to the upper are formed by a sensor moved in the central sleeve, the lower shank which is made with the possibility of coupling through a collet of communication with the piston-pushers of absorbers located in the peripheral sleeves in their lower position and disengaging in the upper one, and the elements of the relationship EDSS a collet arranged in the vertical slits between the peripheral and the central sleeve.  3. The executive body according to claim 1, characterized in that the means for holding the absorbers in the upper position are made in the form of a controlled electromagnet with poles for holding autonomous magnetic conductor pistons-pushers located in peripheral sleeves and which are the supports of the absorbers, and the means for lifting the absorbers from the lower position to the upper one is made in the form of a pneumatic drive formed by the same piston-pushers and peripheral sleeves, the lower part of each of which is connected to the gas through the central sleeve howl controlled pressure manifold, and the top - the backbone low (atmospheric) pressure.

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