JPS605917B2 - Pressurized water reactor power control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides that control rods over the vertical height of the reactor 0 are positioned to compensate for the difference in axial neutron east, and that this neutron east is localized in the upper and lower regions of the core. Two groups of control rods are arranged, each of which is detected by at least one measuring point for the desired power output, and which are provided with neutron absorbers over substantially the entire core, the first one being arranged to maintain a predetermined coolant temperature.
The first control group is positioned virtually exclusively in the upper region of the core, whereas the second control group for compensating for the reaction of fuel temperature on the reactivity of the core is positioned over virtually the entire height of the core. The present invention relates to an output control device for a pressurized water reactor whose position is adjusted by

Such devices are for example "VGBKemkraft-we
rkssemlnarl970'', pages 57 to M.

Swiss Patent No. 508,966 also describes the compensation of xenon radiation in pressurized water reactors, which is normally compensated for by changes in the concentration of boric acid in the coolant, by means of a special control system for this purpose. This compensation is done in such a way that the power increase due to the reduction in xenon wing action caused by the combustion of xenon is avoided by the insertion of control rods, as detailed in the specification. This makes it possible to adjust the positions of the two aforementioned control ray groups independently of the effect of xenon, as if it were not present at all. Furthermore, according to Swiss Patent No. 508966,
It is also known to use so-called part-length control birches, which are provided with neutron-absorbing material only over part of their length.

This control group serves to improve the power distribution throughout the core based on internal measurements of the neutron flux within the reactor. The prerequisite in this case is that the locally high power density is influenced only by the part-length control thread. This is because a control system in which neutron-absorbing material is provided over the entire height of the reactor core cannot exert an effective effect only on problematic areas. Such a view is discussed in U.S. Patent No. 30812.
It is also described in the specification of No. 48, and here the object is a gas-cooled nuclear reactor in which the east distribution of neutrons in the moderator is adjusted by a part-length control lever.

In one embodiment of this specification, a control rod extending over the entire height of the reactor core is provided with a neutron absorber at both ends, and the absorber is inserted into one core machine and the absorber is withdrawn from the opposite core end. It connects. Thereby, the neutron east distribution must be adjusted so that the output output does not change as a whole. In other embodiments of this specification, the effect of this machine is achieved by using two part-length rods provided with absorbers, one at the lower end of the reactor core and the other at the upper end of the reactor core through a coupling with a drive machine. It is obtained by installing it. However, compensation for output fluctuations in all directions of the shaft constructed in this manner requires a considerable expense because a part-length control rod must be provided in addition to the control rod for normal output control. Federal Republic of Germany Patent Application Publication No. 1614702 discloses that the nuclear reactor 'D is divided into two to three regions, their outputs are measured individually, and each region is divided so that the average value of each region is the same. A control system for nuclear reactor equipment is described that controls the output of nuclear reactors.

Therefore, when a deviation occurs, the control rods of each region are controlled in the same direction as the control rods of the entire reactor in the case of power fluctuation. However, such control is only possible if the control rods are arranged in individual areas such that they can be inserted from both sides only to about half the depth of the furnace. Therefore, such control is not possible in a control system in which the position adjustment extends from one side to the entire core. Furthermore, such a control has the disadvantage that it requires a greater number of control rods than in pressurized water reactors of the type mentioned at the outset. Therefore, especially when the control lever drive mechanism has to be operated frequently, the number of failure sources increases. It is an object of the invention to compensate for the axial inhomogeneities of the power distribution which occur in large nuclear reactors, especially those caused by xenon poisoning and which give rise to so-called It's about doing. This purpose, according to the invention, is such that for a core height of at least 3.5 skin, the difference between the upper and lower measuring points can be determined via a delay element to a set value for the adjustment position of the second control group. guided by the transmitter, the position set point is adjusted in the direction of increasing insertion depth of the second control group when the total thermal power increases and when the local power in the upper part of the core decreases;
This is achieved by simultaneously starting the movement of the first control rod group in the withdrawal direction via the coolant temperature control circuit.

By providing two measurement points, it is possible to timely detect differences in the power distribution in the direction of the bag that cause vibrations and to automatically deal with them.

This is achieved by changing the power distribution by adjusting the position of the existing control rods. This takes place via a delay element, so that a control effect particularly suitable for slow output fluctuations is achieved. What is important for the device of the present invention is that
The position setpoint is applied only to the two control beam groups that are adjusted over the entire height of the core, while the other control beam group is adjusted in the upper region to prevent changes in overall power caused by position variations in the other group. be compensated for. The device of the invention also differs from the graphite-moderated gas-cooled high temperature furnace described in GB 1284871. In other words, in this high-temperature reactor, position adjustment of the control rods is only useful for regulating the discharge temperature of the cooling gas to a steady state, that is, an average temperature in a state where there is no output fluctuation. Adaptation to load fluctuations is achieved in this high-temperature reactor by changing the amount of coolant. There is no mention of a xenon effect or a compensation effect for axial non-uniformity of the power distribution. The more precisely the output measuring device is manufactured, the more accurately the output control in the device of the present invention is performed.

For this reason, it is preferable to provide fixed points on both sides in the internal metering device of the core. Furthermore, the power may be detected with sufficient accuracy outside the reactor pressure vessel, taking into account that, for example, the external instrumentation can be configured to be especially reliable and precisely calibrated by maintenance, replacement, etc. Conceivable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings. The drawings show a control system for a pressurized water reactor based on the present invention.

A pressurized water reactor is a reactor pressure vessel 1 in which a reactor core 2 is placed.
have.

Since this pressurized water reactor is designed to have an output of 1200 MWe, the height of the core 2 reaches more than 3.5 degrees, for example, 3.9 degrees. An external coolant circuit 3 is connected to the reactor pressure vessel 1 . At least one steam generator 4 is connected to this coolant circuit 3, into which light water used as primary coolant is pumped by a main coolant pump 5. The steam generator 4 is supplied with water from a water supply conduit 6,
The steam is directed via conduit 7 to a turbine (not shown). '400 generated in the core 2 of a pressurized water reactor
Control rods with neutron absorbing material are used to control the 0 MW thermal power.

This control rod can be adjusted over the entire height of the core 2. A total of about 50 control rods are evenly distributed in the core 2, which has a substantially circular cross section. These control rods are formed substantially identically. This is because the length of their active portion, ie, the neutron absorption length, approximately corresponds to the height of the furnace D. The control rods are divided into three groups.

A first control group L', represented by control group 10, is used to keep the coolant temperature constant. This first group L is accommodated exclusively in the upper region 11 of the core, so that as much space as possible can be accommodated at one time. This first group now occupies about 2/3 to 3/4 of all control rods.
The second control rod group D represented by the control rod 14 compensates for the feedback phenomenon of heating material temperature to reactivity.

For this purpose, the control rods of the second group ○ can be adjusted over the entire height H' of the reactor core 2, as shown at 15. The control rods of this second group D account for about 1/10 of all control rods. The third group x is represented by control rods 16.

This third group x is used to rapidly and locally control output changes such as those caused by the xenon sheathing action. These control rods can have a relatively small reactivity (so-called gray control rods can be used);
They are inserted completely into the furnace 02 individually or in groups as small as possible (17). The control rods of this third group × are less than 1/4 of all the control rods. This third group X is only an auxiliary one, and it is possible to do without it. The coolant circuit 3 is provided with a measuring point 20 for detecting the coolant outlet temperature from the reactor pressure vessel 1 and a measuring point 21 for detecting the coolant temperature after flowing through the steam generator 4.

This creates an average value location 22 that is used to control the coolant temperature. For this purpose, the actual value of the coolant temperature is compared with the setpoint of a setpoint transmitter 23 and fed to a proportional differential regulator (PD regulator) 25 . This proportional differential regulator 25 is applied to a step-by-step switch 28 via a proportional element 26 having a dead range of ±1°C. This step/step switch 28 adjusts the control shaft 10 of the output area L as shown by the line of action 29, and indicates the current insertion depth of the output area L by means of a position indicator 27. Furthermore, two measuring points 30, 31 are placed in the core 2 for measuring the local power in its upper and lower regions, which are shown in the drawing at the upper left corner for the sake of simplicity. For this purpose, a neutron detector 32 belonging to the in-core regulator 34 is installed in the core 2 in a well-known manner.
is provided. The measured value of the neutron detector 32 detected via the amplifier 33 is transmitted to the so-called combustion distribution controller 35.
This is the basis for the calculations performed in . For example, measurement point 2
The local reactor power in the upper part of the core measured at the measurement point 30 is determined by the calculator 36 from the difference in coolant temperature between 0 and 21 and the rotational speed of the main coolant pump 5. In relation to the ratio and also taking into account the position of the first control group L transmitted from the position indicator 27, the setting values for the power distribution controller 38 are adjusted via the delay element 37. The delay element 37 is provided in order to adapt the position adjustment of the control shaft with a time delay to the operating sequence determined by the reaction of the xenon, thereby avoiding unstable operation due to rapid fluctuations. As shown in the drawing, the temporal relationship of the control action in the delay element 37 is such that there is a delay of one hour when the output increases, and one feeding time when the output decreases. The larger the overall reactor thermal output is, and the shallower the depth of the control rods 10 of the first control rod group L, the greater the power in the upper part of the core. For this purpose, the output distribution controller 38, which consists of two timing elements 38a and 38b and a proportional element 38c having a non-operating region connected in series with the timing element 38b, takes the delay element 37 from the combustion distribution controller 35. The setpoint value provided through is compared with the difference in power measurements at measurement points 30, 31 at the top and bottom of the core. Taking into account the value of the setpoint transmitter 40 for the position of the second control group D, which is connected via the switch 39 and can be controlled, for example, manually or depending on the degree of fuel consumption, an inoperation of ±5. A step-by-step switch 42 is operated via a proportional element 41 with a range, so that the control rod 14 is adjusted if the output distribution is or is likely to be in an undesired state.
The control rods 14 of the second control rod group D are controlled via a switch 39 depending on an external measuring device 43 having two measuring points indicated by sondes 44 and 45 at the upper and lower parts of the L core. You can also do it. The difference from the average value formed by suitable calculations in the amplifier 46 is given as an actual value to the controller 47 and is applied to the power distribution controller 3 via the switch 39.
8 to the subsequently connected elements. Therefore, L
Therefore, when the non-uniformity of the output distribution becomes undesirably large, the control rods 14 of the second control rod group D can be operated. Adjustment of the control rods according to the invention to reduce xenon oscillations can also be assisted by a third control rod group X and injection of deionized or boric acid water into the core.

This third control group x and water injection help control the toxic effects of xenon and fuel wastage. For this purpose, a boric acid liquid line 48 and a deionized (pure water) line 49 are used, which are connected to the coolant circuit 3 via a coolant pump 50. The control valves 51, 52 associated with these conduits are opened by a control drive 53. This control drive 53 is activated depending on the difference between the set value for the position of the D area, which depends exclusively on the heat output (calculator 36), on the one hand, and the actual position, coming from the transmitter 54 associated with the step-by-step switch 42. Receive direct orders. As another value, a setting value can be given from the setting device 60. However, the control drive 5
3 can also be operated directly by the final position notification of the position indicator 57 attached to the step/step switch 56 for the xenon region X control rod 16. This is preselected via switch 58. “Life” on the stick 16 ±
Since a proportional element 55 with a dead area of 20 degrees is connected, the control rod is only driven at a relatively large value.

The above-mentioned step-by-step switch 56 is a proportional element 5.
5. If the x region reaches a certain limit value, the control drive 53 is actuated by the step-by-step switch 56 via the position indicator 57. Measurement point 30, . 31 belongs to the internal instrumentation equipment of the nuclear reactor core 2, unlike what is shown in the figure.

These measurement points 30, 31 therefore directly measure the neutron east and the local power of the upper and lower parts of the reactor D. Each of these is provided with a number of sondes 32. In the example, three sondes are shown that can be evaluated by the two-of-three system for each measurement point. In that case, the sum or another function, for example the second largest value, can also be chosen. When the reactor power is adjusted by adjusting the control rods 14, the control rods 10 are driven by coolant temperature control, so if the difference between the final values of the fixed points 30 and 31 on both sides exceeds a predetermined tolerance, Adjustment of the control rod 14 initiates movement of the control rod 10. This also applies to the control carried out by the switch 39 as a function of the measured values of the probes 44, 45 of the external measuring device 43. In this way, the difference between high and low output values can be suppressed such that no vibrations caused by xenon are present.

[Brief explanation of drawings]

The drawing is a system diagram showing a control rod control system of a pressurized water reactor based on the present invention. 1...Reactor pressure vessel, 2...Reactor core,
3... Coolant circuit, 4... Steam generator, 30...
...Measurement point at the top of the core, 31...Measurement point at the bottom of the core, 37...Delay element, 38...Output distribution controller, 40...Position set value transmitter , L...first control rod group, D...second control rod group.

Claims (1)

[Claims] 1 Control rods over the axial height of the core are adjusted to compensate for differences in the axial neutron flux, which flux is determined by at least one measurement point each for the local power in the upper and lower regions of the core. Two groups of control rods are detected and provided with neutron absorbers over the entire height of the core, with the first group of control rods being positioned exclusively in the upper region of the core to maintain a predetermined coolant temperature. On the other hand, the second control rod group, which compensates for the reaction of fuel temperature on core reactivity, is positioned in the power control system of a pressurized water reactor whose position is adjusted over the entire height of the reactor core. The difference between the measured values at the point 30 and the lower measuring point 31 is led via the delay element 37 and the power distribution controller 38 to the set point transmitter 40 for the adjustment position of the second control rod group D, increasing the total heat output P_R. When the local power decreases in the upper part of the core, this position set value is adjusted in the direction of increasing the insertion depth of the second control rod group D, and at the same time the position setting value is adjusted in the direction of increasing the insertion depth of the second control rod group D. An output control device for a pressurized water reactor, characterized in that it starts movement of one control rod group L in a withdrawal direction.