Method for controlling part strength control element assembly to enable turbine load-following

Abstract

The present invention relates to a method for controlling a part strength control element assembly to enable turbine load-following, comprising the steps of: identifying operation driving characteristics of a part strength control element assembly according to turbine loads through simulation of power plant-simulation calculations with varying turbine load; determining a maximum insertion position within the core of the part strength control element assembly on the basis of the operation driving characteristics; deriving a target position of the part strength control element assembly according to turbine load on the basis of the maximum insertion position; and controlling the insertion position of the part strength control element assembly according to the target position.

Description

Control method of a partially reinforced control rod assembly for turbine load tracking

[0001] The present invention relates to a control method for a partially reinforced control rod assembly for turbine load tracking.

[0002] The reactor control system of CE-type nuclear power plants, OPR1000, and APR1400 nuclear power plants, operates the control rod assembly through automatic control logic so that the reactor can track changes in turbine load. This automatic control logic applies only to the full-strength control element assembly among the control rod assembly composed of part-strength and full-strength control rod assemblies, while the part-strength control element assembly (PSCEA) is manually operated when necessary to control the axial power distribution of the reactor.

[0003] That is, when the reactor output changes due to a change in turbine load, the reactor control system must automatically control the reactivity (reactor output), and the operator must manually drive (insert / withdraw) the partial control rod assembly to stably control the axial output distribution caused by the output change.

[0004] Therefore, if frequent turbine load changes, such as daily load following operation, are required, the burden on the operator due to manual operation of the partial steel control rod assembly can be greatly increased.

[0005] Accordingly, an object of the present invention is to provide a method for controlling a partially reinforced control rod assembly for turbine load tracking.

[0006] The above object of the present invention is achieved by a method for controlling a partial steel control rod assembly for turbine load tracking, comprising: a step of identifying the operation and driving characteristics of a partial steel control rod assembly according to a turbine load through a power plant simulation that changes the turbine load; a step of determining a maximum insertion position of the partial steel control rod assembly in a core based on the operation and driving characteristics; a step of deriving a target position of the partial steel control rod assembly according to the turbine load based on the maximum insertion position; and a step of controlling the insertion position of the partial steel control rod assembly according to the target position.

[0007] The above driving characteristics may include at least one of (1) whether the partial control rod assembly is inserted / withdrawn according to a change in turbine load, (2) the position of the partial control rod assembly within the core having excellent performance in controlling output and axial power distribution, (3) whether there is a proportionality between the minimum output and the maximum insertion position of the partial control rod assembly during load following, and (4) whether there is a difference in the maximum insertion position of the partial control rod assembly according to output, core cycle, and burnup.

[0008] The maximum insertion position of the above partial control rod assembly in the core can be provided according to output, cycle, and burnup.

[0009] The above target position can be determined using the maximum insertion position of the partial control rod assembly for each core length, cycle and burnup, turbine load, and core power of the current reactor.

[0010] The above target position is determined by the formula target position = (core length - pslimit) / A*(BA)+pslimit, where pslimit is the maximum insertion position of the partial control rod assembly by cycle and burnup, A is the minimum turbine load, and B may be the core power of the current reactor.

[0011] In the insertion position control of the partial force control rod assembly, the method may include a step of comparing the target position with the current position to determine a deviation value and a deviation direction; and a step of determining the insertion speed and direction of the partial force control rod assembly according to the deviation value and the deviation direction.

[0012] According to the present invention, a method for controlling a partially reinforced control rod assembly for turbine load tracking is provided.

[0013] Figure 1 is a flowchart of a control method of a partial steel control rod assembly for turbine load tracking according to one embodiment of the present invention.

[0014] Figure 2 shows the maximum insertion position of the partial control rod assembly by combustion degree in one cycle.

[0015] Figure 3 shows the maximum insertion position of the partial control rod assembly by combustion degree in 8 cycles.

[0016] The present invention will be described in more detail with reference to the drawings below.

[0017] The attached drawings are merely examples intended to more specifically illustrate the technical concepts of the present invention, and therefore, the scope of the present invention is not limited to the attached drawings. Furthermore, the attached drawings may exaggerate the size and spacing of components to illustrate the relationships between components.

[0018] Due to the insertion characteristics of the control rods, which are driven from the top, a decrease in reactor power may result in a bias in power toward the lower portion of the reactor. At the same time, a decrease in temperature at the reactor outlet (i.e., the upper portion of the reactor) may also result in a bias in power toward the upper portion of the reactor.

[0019] Due to these complex characteristics, each nuclear power plant utilizes various control rod designs and control methods to control the reactor axial power distribution when output changes. The present invention analyzes and utilizes these physical characteristics through simulation methods to propose a control logic for a partially reinforced control rod assembly capable of automatically controlling the axial power distribution when adjusting the output of various types of nuclear power plants.

[0020] The present invention will be described in detail with reference to the drawings below.

[0021] Referring to FIG. 1, a method for controlling a partial control rod assembly for turbine load tracking according to the present invention is described.

[0022] First, the operating characteristics of the partial control rod assembly are identified according to the turbine load through a power plant simulation that changes the turbine load (S100).

[0023] In this step, the physical correlation between the reactor power / power distribution and the partial control rod assembly according to the turbine load change simulation is analyzed.

[0024] In this step, simulations are performed based on output change scenarios. Examples of output change scenarios include, but are not limited to, daily load-following operation.

[0025] Daily load following operation is a simulation that reduces the generator output from 100% to 50% for 2 hours, maintains 50% output for 6 hours, and then reduces back to 100% output for 2 hours, performing the simulation over a 24-hour cycle.

[0026] During the simulation, the reactor power is automatically controlled by the reactor control system, and the axial power distribution is also automatically adjusted by the partial steel control rod assembly to maintain the target power distribution.

[0027] These simulations are performed under various conditions (cycle, burnup) to analyze the physical characteristics (position change, etc.) of the partial control rod assembly when the turbine load changes in various nuclear power plant types.

[0028] The driving characteristics obtained through such analysis include at least one of the following, and preferably all four of them.

[0029] (1) Whether the partial control rod assembly is inserted / withdrawn according to changes in turbine load

[0030] (2) Location of the partial control rod assembly within the core with excellent power and axial power distribution control performance.

[0031] (3) Whether there is a proportionality between the minimum output and the maximum insertion position of the partial control rod assembly when following the load, and

[0032] (4) Whether there is a difference in the maximum insertion position of the partial control rod assembly according to output, core cycle, and burnup.

[0033] Next, based on the identified driving characteristics, the maximum insertion position of the partial control rod assembly within the core is determined (S200).

[0034] The maximum insertion position of the partial control rod assembly in the core can be determined by power, cycle, and burnup.

[0035] Below, the length of the reactor core is explained as an example of 380 cm, but the present invention is not limited thereto.

[0036] The driving range of the partial control rod assembly based on the previously identified driving characteristics (physical characteristics) can be limited to, for example, the upper half of the reactor core (180 to 380 cm), and the maximum insertion position can be determined according to the core cycle and burnup as shown in FIGS. 2 and 3.

[0037] Figure 2 shows the maximum insertion position of the partial control rod assembly by combustion degree in one cycle, and Figure 3 shows the maximum insertion position of the partial control rod assembly by combustion degree in eight cycles.

[0038] Figure 2 shows the maximum positions of the partial control rod assemblies that can be inserted into the core at the burnup level of Cycle 1 (initial core) (in the case of load following with turbine output reduced to 50%). That is, the entire reactor core is 380 cm high from the bottom, and the control rods inserted from the top can be inserted to around 270 cm from the bottom.

[0039] Figures 2 and 3 were obtained using a nuclear power plant system performance analysis program. To obtain Figures 2 and 3, the system performance analysis program automatically and manually adjusted the control rod assembly (automatic control according to output), the partial reinforcement rod assembly (manual control), and the boron concentration (manual control), and thus obtained the insertion positions of the partial reinforcement rod assembly that controlled the optimal output and output distribution. These positions were performed under various burnup conditions, and the optimal positions were selected to obtain Figures 2 and 3.

[0040] The y-axis of FIG. 2 and FIG. 3 represents the maximum insertion position of the control rod assuming 50% load following, and the x-axis represents the burnup (beginning of cycle - middle of cycle - end of cycle) in the corresponding cycle. In other words, FIG. 2 and FIG. 3 illustrate the determination of the optimal (power and power distribution control performance) position of the partial control rod assembly at 50% output by identifying the operating characteristics of the partial control rod assembly through a nuclear power plant simulation code in a load following operation that reduces power from 100% to 50% and vaporizes to 100%.

[0041] For example, looking at Figure 2 for Cycle 1, when the output drops to 50% during load following, the partial control rod assembly is positioned approximately 270 cm from the bottom to the top of the core. Looking at Figure 3 for Cycle 8, the partial control rod assembly can be inserted up to 270 cm from the core up to 10,000 MWD / MTU, and in the 10,000 to 15,000 MWD / MTU range, it can be inserted linearly from 270 to 190 cm.

[0042] In addition, from the analysis results such as those in FIGS. 2 and 3, the operating range of the partial control rod assembly can be limited to the upper half of the reactor core (180 to 380 cm).

[0043] Afterwards, based on the determined maximum insertion position, the target position of the partial control rod assembly according to the turbine load is derived (S300).

[0044] The target position can be determined using the core length, the maximum insertion position of the partial control rod assembly for each cycle and burnup, the turbine load, and the core power of the current reactor.

[0045] The target position can be determined by the following equation:

[0046] Target position = (core length-pslimit) / A*(BA)+pslimit

[0047] Here, pslimit is the maximum insertion position of the partial control rod assembly by cycle and burnup, A is the minimum turbine load, and B is the core power of the current reactor.

[0048] Finally, the insertion position of the partial force control rod assembly is controlled according to the derived target position (S400).

[0049] In the insertion position control of the partial force control rod assembly, the steps may include (1) comparing the target position and the current position to determine a deviation value and a deviation direction, and (2) determining the insertion speed and direction of the partial force control rod assembly according to the deviation value and the deviation direction.

[0050] When the target position of the partial control rod assembly to be controlled is produced from the formula of the previous step, the insertion speed and direction of the control rod are determined based on the value of the deviation and the minus (-) / positive (+) compared with the current position of the partial control rod assembly, and the partial control rod assembly is controlled based on the determined value to adjust the position of the partial control rod assembly.

[0051] When turbine load following operation is required, by using the partial control rod assembly control logic according to the present invention together with the existing reactor control system, reactor output and axial power distribution control are possible without burdening the operator with the control of the partial control rod assembly.

[0052] The above-described examples serve as illustrative examples of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate the potential for various modifications and implementations of the present invention. Therefore, the technical protection scope of the present invention should be defined by the appended claims.

Claims

1. In a control method of a partial steel control rod assembly for turbine load tracking, A step of identifying the operating characteristics of a partial steel control rod assembly according to the turbine load through a power plant simulation that changes the turbine load; A step of determining the maximum insertion position of a partial control rod assembly within the core based on the above driving characteristics; A step of deriving a target position of a partial control rod assembly according to a turbine load based on the above maximum insertion position; and A control method comprising a step of controlling the insertion position of a partial force control rod assembly according to the above target position.

2. In paragraph 1, The above driving characteristics are (1) Whether the partial control rod assembly is inserted / withdrawn according to changes in turbine load (2) Location of the partial control rod assembly within the core with excellent power and axial power distribution control performance. (3) Whether there is a proportionality between the minimum output and the maximum insertion position of the partial control rod assembly when following the load, and (4) Whether there is a difference in the maximum insertion position of the partial control rod assembly according to output, core cycle, and burnup. A control method comprising at least one of:

3. In paragraph 2, A control method in which the maximum insertion position of the above-mentioned partial control rod assembly in the core is provided according to output, cycle, and burnup.

4. In paragraph 3, The above target location is, A control method determined using the maximum insertion position of the partial control rod assembly according to core length, cycle and burnup, turbine load and core power of the current reactor.

5. In paragraph 4, The above target location is Target position = (core length - pslimit) / A*(BA)+pslimit, Here, pslimit is the maximum insertion position of the partial control rod assembly by cycle and burnup, A is the minimum turbine load, and B is the control method for the current core power of the reactor.

6. In paragraph 5, In the insertion position control of the partial force control rod assembly, A step of comparing the target position and the current position to determine the deviation value and deviation direction; and A control method comprising a step of determining the insertion speed and direction of a partial force control rod assembly according to the above deviation value and deviation direction.

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