CN118919109A - Rapid power reduction method and control system - Google Patents

Abstract

A rapid power reduction method provides a plurality of groups of ash control rods, calculates a power-rod position slope factor F=delta P/delta S, wherein delta P is the relative power change percentage of a reactor core, and delta S is the number of control rod downshifts; when a given power-down triggering condition is reached, calculating the number delta N= (P ₀-P_t)/F of the needed next step jump of the ash control rod, wherein P ₀ is the relative power percentage of the current reactor core, and P _t is the power percentage of the reactor core matched with the secondary side power under the power-down triggering condition; and further calculating a target rod position N _c＝N₀ -delta N, wherein N ₀ is the current gray control rod position, setting the number of steps corresponding to the complete downward insertion of a single group of gray control rods as N, and determining the number k of gray control rod groups which need to be controlled to be downward inserted according to kn < N _c is less than or equal to (k-1) N. The method can quickly reduce the reactor core power under the transient condition that the secondary side power is reduced by a small extent, avoid the shutdown triggered by the too low liquid level of the steam generator, and improve the running economy of the reactor. The invention also provides a rapid power-down control system.

Description

Rapid power reduction method and control system

Technical Field

The invention belongs to the field of nuclear power, and particularly relates to a rapid power reduction method and a control system.

Background

The nuclear power plant reactor has a Rapid Power Reduction System (RPRS) for coping with large load change transients such as turbine trips. The existing RPRS system can realize the rapid drop of the power of the reactor core by controlling the preset black rod to drop, can rapidly reduce the power of the reactor core to 50% RTP (below rated heat power), and then realizes the power matching of the first loop and the second loop under the common cooperation of control systems such as a side-row system, a rod control system and the like. However, when an event with small secondary side load change occurs, such as a trip transient of a single main feed water pump occurs under a full-power operation condition, the RPRS action cannot be triggered, and in such a case, the transient development process may cause that the narrow-range low-liquid-level margin of the evaporator (SG) is too low, and the risk of triggering shutdown exists. Therefore, the control method capable of realizing small-amplitude power reduction aiming at transient state has positive significance for effectively aiming at the tripping working condition of a single main feed pump and improving the safety of the operation of the reactor.

Disclosure of Invention

The invention aims to provide a rapid power reduction method which can realize rapid power reduction of a reactor with smaller amplitude. The invention also provides a rapid power-down control system.

According to an embodiment of one aspect of the present invention, there is provided a rapid power reduction method including the steps of: providing a plurality of groups of ash control rods, calculating a power-rod position slope factor F, wherein F=delta P/delta S, delta P is the relative power change percentage of the reactor core, delta S is the number of control rod inserting steps, and F is updated along with the cyclic burnup of the reactor; giving a power-down triggering condition, wherein the power-down triggering condition comprises abrupt change of a secondary side load; when the power reduction triggering condition is reached, calculating the number delta N, delta N= (P ₀-P_t)/F of the next step jump needed by the ash control rod, wherein P ₀ is the current core relative power percentage, and P _t is the core power percentage matched with the secondary side power under the power reduction triggering condition; calculating a target rod position N _c,N_c＝N₀ -delta N, wherein N ₀ is the current gray control rod position, and the ascending is positive and the downward insertion is negative; and setting the corresponding step number of the complete downward insertion of the single group of ash control rods as N, and controlling the complete downward insertion of k groups of ash control rods, wherein kn is less than N _c and less than (k-1) N.

The method can quickly control the reactor speed to be reduced when the secondary side load is insufficient to trigger the small-amplitude change of the RPRS action so as to realize the primary and secondary side power matching, so that the unit enters a stable running state, and the accident risk caused by the too low liquid level of the Steam Generator (SG) is avoided.

Further, in some embodiments, the update period of the power-bar bit slope factor F is no longer than 2000MWd/tU. In different burnup stages, the influence of the ash control rod on the power is different, and the F is updated to realize more accurate power control.

Further, in some embodiments, the step of correcting the power-rod slope factor according to the power-rod curve is further included in calculating ΔN. In the running process of the reactor, the control rods can be positioned at different rod positions, and under some working conditions, the initial rod position has an influence on the change rate of power along with the rod position, and the control rods need to be corrected according to actual conditions.

Further, in some embodiments, P _t is the secondary side core power percentage when a main feedwater pump is tripped.

Further, in some embodiments, the P _t is no more than 50%. The RPRS intervention can reduce the reactor power to below 50%, and the ash control rod intervention scene is a transient state which does not trigger the RPRS.

Further, in some embodiments, the gray control rods are configured with 4 groups.

Further, in some embodiments, after the k groups of ash control rods are fully inserted, the method further includes a step of controlling adjacent ash control rods to reconstruct an overlapping step. Under normal conditions, a certain overlapping step exists between the adjacent ash control rod groups, when the ash control rods are inserted in an emergency, the overlapping step relation is broken, and the overlapping step relation needs to be rebuilt so as to restore the normal control of the ash control rods.

Further, in some embodiments, the steam generator level margin is no less than 5% after the reduced power triggering condition is reached.

According to an embodiment of another aspect of the present invention, there is provided a rapid power reduction control system, the system including a secondary side detection device, a memory, a processor, and an ash bar control system, wherein the secondary side detection device detects a reactor secondary side load state; the ash rod control system comprises a driving device and a plurality of groups of ash control rods, wherein the driving device drives the plurality of groups of ash control rods to ascend or descend; the memory stores a control program which, when executed by the processor, enables the rapid power reduction system to implement the rapid power reduction method provided in any of the foregoing embodiments.

Drawings

FIG. 1 is a schematic diagram of a fast power down control system according to an embodiment;

FIG. 2 is a schematic diagram of a power-bar graph in an embodiment;

FIG. 3 is a schematic diagram of a power-stick diagram for different burnup phases in an embodiment;

FIG. 4 is a graph illustrating power versus rod position for different initial rod positions according to one embodiment;

FIG. 5 is a graph showing power versus rod position at different initial powers in an embodiment;

FIG. 6 is a graph of power change under an accident condition for a pair of examples;

FIG. 7 is a graph showing SG level change curves under accident conditions in a comparative example;

FIG. 8 is a graph illustrating power variation during an accident condition according to one embodiment;

FIG. 9 is a graph showing SG level change curves under accident conditions in an embodiment.

Meaning of reference numerals: 1-a core; 2-ash control bar; 3-a driving device; 4-a steam generator; 5-a main pump; 6-a steam turbine; 7-a condenser; 8-a main feed water pump set; 9-a controller; 10-memory.

The above drawings are provided for the purpose of explaining the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, and are not intended to limit the present invention. For simplicity of illustration, the above figures show only schematically the structures related to the technical features of the present invention, and not all the details and the complete structures are drawn strictly to the actual scale.

Detailed Description

The invention will now be described in further detail with reference to the accompanying drawings by means of specific examples.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment herein. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments limited to the same embodiment. Those skilled in the art will appreciate that embodiments herein may be combined with other embodiments without structural conflict.

In the description herein, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and the like are to be construed broadly and may be, for example, mechanical structures connected or signal-connected; the two parts can be movably connected, or can be fixedly connected or integrated. The specific meaning of the above terms in the embodiments of the present application will be understood by those skilled in the art according to specific circumstances.

In the description herein, terms such as "upper," "lower," "left," "right," "transverse," "longitudinal," "height," "length," "width," and the like that indicate an azimuth or positional relationship are intended to accurately describe the embodiments and simplify the description, and do not limit the details or structures involved to having to have a particular azimuth, mount or operate in a particular azimuth, and are not to be construed as limiting embodiments herein.

In the description herein, the terms "first," "second," and the like are used merely to distinguish between different objects and should not be construed as indicating relative importance or defining the number, particular order, or primary and secondary relationships of the technical features described. In the description herein, the meaning of "plurality" is at least two.

The general structure of a conventional domestic pressurized water reactor power plant is understood in connection with fig. 1 and comprises a reactor core 1, wherein a primary loop cooling medium conveys heat released by fuel rods in the reactor core 1 to a steam generator 4, the primary loop cooling medium exchanges heat with a secondary loop cooling medium in the steam generator 4 to heat the secondary loop cooling medium into steam, and then the primary loop cooling medium with reduced temperature returns to the reactor core 1 for circulation under the action of a main pump 5; the steam formed by the two-circuit cooling medium in the steam generator 4 is conveyed to the steam turbine 6 to generate electricity, then is cooled to be liquid in the condenser 7, and the condensed two-circuit cooling medium is conveyed back to the steam generator 4 through the main water supply pump set 8 to complete circulation.

When accidents such as tripping of the steam turbine 6 occur in the secondary loop, the load on the secondary side is rapidly reduced, and if the output power of the reactor core 1 is kept unchanged, the coolant in the steam generator 4 is rapidly reduced, so that the accident risk is generated. Therefore, a fast power reduction system (RPRS) is usually provided in the pressurized water reactor at present, and when a large-scale load change transient state such as tripping of the steam turbine 6 occurs, the RPRS system can quickly insert a certain number and position of black control rods into the reactor core 1, so that the reactor core power can be quickly reduced. In general, the black control rod is made of a material with strong neutron absorption capacity such as silver-indium-cadmium alloy, so that neutrons in the reactor core can be absorbed in a large amount, and the reactor core power can be reduced rapidly. The RPRS system can quickly reduce the reactor core power to below 50% of rated heat power (RTP) and prevent accidents caused by large abrupt changes of secondary side load. And then, under the common cooperation of control systems such as a side-row system, a rod control system and the like, the power matching of the first loop and the second loop is realized.

However, in the reactor operation process, besides the transient state that the secondary side load is greatly reduced due to tripping of the steam turbine 6 and the like, the transient state that the secondary side load is slightly reduced due to tripping of a single main water pump in the main water supply pump group 8 and the like exists.

In one comparative example, as shown in fig. 6, when one of the three main feedwater pumps is tripped and the secondary side power is reduced by about 40%, the RPRS system does not intervene in the rapid, substantial power reduction process of the core 1, and it takes about 10 minutes to adjust the reactor power by conventional methods to achieve the primary and secondary side power matching. Before the power of the primary side and the power of the secondary side are matched, the output power of the reactor core 1 is larger than the power load of the secondary side, so that the secondary loop cooling medium in the steam generator 4 is excessively evaporated, and the narrow-range water level in the steam generator 4 is quickly reduced. As shown in fig. 7, the water level in the steam generator 4 is reduced to the minimum about 5 minutes after the trip of the single main feed pump, and the minimum margin from the SG narrow range low water level shutdown line is only 2.7%, which creates a high risk for normal operation of the reactor. In this state, if the conventional control method fails to timely reduce the output power of the core 1 or the circulation system of the two loops fails, a shutdown accident is likely to be caused, resulting in serious consequences.

In order to solve the above problems, an embodiment of one aspect of the present invention provides a rapid power reduction method.

As shown in fig. 1, the reactor is provided with an gray rod control system including a plurality of sets of gray control rods 2 and a driving device 3 in addition to the black control rods, and the gray control rods 2 may be inserted into the core 1 under the driving of the driving device 3. The ash control rods 2 are made of a material with weak neutron absorption capacity such as stainless steel, so that neutron dose in the reactor core 1 can be reduced, but the neutron absorption performance of the ash control rods is weaker than that of the black rods, so that remarkable power distortion is not caused, and complete shutdown of the reactor core 1 is not caused. In normal operating conditions, the output power or the backup reactivity of the reactor can be regulated by regulating the rod position of the ash control rod inserted into the reactor core in different cyclic burnup phases of the fuel, and in general, the movement of the ash control rod 2 in the fuel burnup period is gradually regulated in small amplitude according to the burnup state.

In the embodiment, in order to cope with the transient state that the load of the secondary side is reduced by a small extent (usually by about 30% -40%) caused by tripping of a single main water supply pump in the main water supply pump set 8, a plurality of groups of ash control rods 2 can be controlled by the driving device 3 to be quickly and completely inserted into the reactor core 1, so that the quick power reduction of the reactor core 1 is realized.

Specifically, the number of groups of gray control rods 2 that need to be inserted is determined by:

First, the power-rod-bit slope factor F, f=Δp/Δs is analyzed, where Δp is the percentage of core relative power change and Δs is the number of control rod downshifts. Wherein there may be some variation in F at different stages of the reactor cycle burn-up, so the specific value of F should be updated with the cycle burn-up. In a preferred embodiment, the update period of F is no longer than 2000MWd/tU. F can be determined according to a power-rod position curve, wherein the power-rod position curve can be actually measured in the running process of the reactor, and can also be determined in a simulation calculation mode. In the preferred embodiment, the specific value of F should be specifically modified based on the initial rod position of the gray control rods 2 in the core 1, the effect of the initial power of the reactor on the power-rod position curve.

Next, when the secondary side load suddenly changes and reaches the triggering condition of the rapid power reduction method, the total number of downward inserted steps delta N, delta n= (P ₀-P_t)/F required by the transient ash control rod 2 is calculated, wherein P ₀ is the current core relative power percentage, and P _t is the core power percentage matched with the secondary side power under the power reduction triggering condition.

Next, a target rod position N _c,N_c＝N₀ - ΔN is determined, where N ₀ is the current gray control rod position, to rise positive and to insert negative.

Subsequently, the number of gray control rods 2 inserted into the core 1 is determined. The number of steps corresponding to the complete downward insertion of a single group of ash control rods is set as N, and the number k of ash control rods which need to be inserted downward in the rapid power reduction process meets kn < N _c + (k-1) N. During normal operation of the reactor, different groups of ash control rods 2 are inserted into the core 1 one by one or lifted from the core 1 as the cycle burns up, while during rapid power down control, k groups of ash control rods need to be inserted into the core 1 quickly and completely.

Under normal conditions, a certain number of overlapping steps exist between adjacent gray control rod sets so as to maintain normal regulation of reactor power. Thus, in the preferred embodiment, after the k sets of gray control rods are quickly and fully inserted into the core 1, adjacent gray control rods 2 are next controlled to be quickly inserted downward to reestablish the normal overlapping step relationship.

In the preferred embodiment, the above control procedure is written as a control program stored in the memory 10, and when the controller 9 detects that the secondary side load state reaches the trigger condition of rapid power reduction by the secondary side detection means, the control program stored in the memory 10 can be executed by the controller 9 to instruct the driving means 3 to automatically implement the rapid power reduction method provided in the above embodiment.

In a preferred embodiment, 157 sets of fuel assemblies are loaded in the core 1, 4 sets of gray control rods 2 are provided, and under normal conditions, the 4 sets of gray control rods 2 move in sequence, and each set of gray control rods 2 falls completely into the core 1 for a corresponding step number of-181 steps (positive in rising and negative in inserting).

Under normal operating conditions, the measured power-rod position curve is shown in FIG. 2, with the power-rod positions being approximately piecewise linear.

In different burnup states, the measured power-rod position curves are shown in fig. 3, when the curve interval of the different burnup states is smaller, the update period of the slope factor F can be set longer along with the change of burnup, and when the curve interval is larger, the update frequency of the slope factor F in the interval is higher, and in a preferred state, the update period of the F is not longer than 2000MWd/tU.

The calculation results of the power-rod position curves under different initial rod positions are shown in fig. 4, the curves of the different initial rod positions are approximately parallel in most intervals, and the error of calculating by taking the same slope factor is within an acceptable range. Only after all four groups of gray control rods 2 are inserted, a certain deviation exists, but in this state, the power limit of the gray control rods 2 to the reactor core 1 is already close to the limit, and the influence of the deviation of F on the result of the power limit is within an acceptable range.

When an incident transient occurs, the reactor may be at different operating powers. The calculated power-rod position curves are shown in fig. 5, and the curves of different initial powers in most intervals are approximately parallel, and can be calculated by adopting the same F value. If the curve parallelism of different initial powers is low, the value of F needs to be determined according to the power-rod position curve under the corresponding initial power.

Assuming that one of the three main water pumps of the main water pump group 8 trips at the initial stage of a certain cycle in a state that the power level is 100% rtp, the secondary side load is instantaneously reduced to 70% of the original load, and the initial rod position of the ash control rod 2 is 90 steps. F=0.1 (% RTP/step) in this state is calculated based on the rod position-power curve in this state.

In order to rapidly reduce the output power of the core 1, to avoid shutdown caused by too low a liquid level of the steam generator 4, rapid power reduction control is implemented as follows.

First, Δn, Δn= (P ₀-P_t)/f= (100-70)/0.1=300 steps are calculated.

Next, the target rod position is calculated, N _c＝N₀ - Δn= -270 steps. The calculation result rises positive and the down-insertion is negative.

181 X 2<270< -181, so the first two groups of gray control rods 2 should be dropped completely into the core 1.

By controlling the rapid power reduction method as described above, the power of the core 1 is changed as shown in fig. 8, and it can be seen that the power of the core 1 is reduced more rapidly than the comparative example shown in fig. 6. In the preferred embodiment, after the first two groups of gray control rods 2 drop into the core quickly, the third group of gray control rods 2 are also inserted into the core quickly, reestablishing the normal overlapping steps to reestablish the power balance on the primary and secondary sides quickly. As shown in fig. 9, since the power of the core 1 is rapidly controlled, the water level in the steam generator 4 is effectively maintained, the minimum margin of the water level is maintained to be more than 10%, and the safety of the reactor is effectively improved.

The above-described control process may be automatically implemented in the form of the controller 9 executing a control program stored in advance in the memory 10.

The above-described embodiments are intended to explain the present invention in further detail with reference to the figures so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present disclosure, the system or method steps involved are optimized or replaced equivalently, and the implementation manners of the different embodiments are combined on the premise that no structural and principle conflict occurs, which falls within the protection scope of the present disclosure.

Claims (9)

1. A rapid power reduction method, comprising the steps of:

Providing a plurality of groups of ash control rods, calculating a power-rod position slope factor F, wherein F=delta P/delta S, delta P is the relative power change percentage of the reactor core, delta S is the number of control rod inserting steps, and F is updated along with the cyclic burnup of the reactor;

Giving a power-down triggering condition, wherein the power-down triggering condition comprises abrupt change of a secondary side load;

When the power reduction triggering condition is reached, calculating the number delta N, delta N= (P ₀-P_t)/F of the next step jump needed by the ash control rod, wherein P ₀ is the current core relative power percentage, and P _t is the core power percentage matched with the secondary side power under the power reduction triggering condition;

Calculating a target rod position N _c,N_c＝N₀ -delta N, wherein N ₀ is the current gray control rod position, and the ascending is positive and the downward insertion is negative;

And setting the corresponding step number of the complete downward insertion of the single group of ash control rods as N, and controlling the complete downward insertion of k groups of ash control rods, wherein kn is less than N _c and less than (k-1) N.

2. The rapid power down method of claim 1, wherein the update period of the power-bar slope factor F is no longer than 2000MWd/tU.

3. The rapid power reduction method according to claim 1 or 2, further comprising the step of correcting the power-rod slope factor according to a power-rod curve when calculating an.

4. The rapid power reduction method according to claim 1 or 2, wherein P _t is the secondary side core power percentage when a main feed pump is tripped.

5. The rapid power reduction method according to claim 1 or 2, wherein P _t is not more than 50%.

6. The rapid power reduction method according to claim 1 or 2, wherein the ash control rods are configured with 4 groups.

7. The rapid power reduction method according to claim 1 or 2, further comprising the step of controlling adjacent ones of said ash control rods to reestablish an overlapping step after controlling k groups of said ash control rods to be fully inserted.

8. A rapid power down method according to claim 1 or 2, characterized in that after the power down triggering condition is reached, the liquid level margin of the steam generator is not lower than 5%.

9. A rapid power-down control system is characterized by comprising a secondary side detection device, a memory, a processor and a gray rod control system, wherein,

The secondary side detection device detects a reactor secondary side load state;

The ash rod control system comprises a driving device and a plurality of groups of ash control rods, wherein the driving device drives the plurality of groups of ash control rods to ascend or descend;

The memory stores a control program which, when executed by the processor, is capable of implementing the rapid power reduction method of any one of claims 1 to 8.