JPS6318151B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of operating a nuclear reactor, such as a boiling water reactor (hereinafter referred to as BWR), and in particular to a method for operating a nuclear reactor suitable for increasing reactor output. This relates to how to drive a car.

[Background of the invention]

In BWR, from the perspective of preventing fuel rod damage due to interaction between fuel pellets and cladding, control rod withdrawal is performed when the linear power density of the fuel rod is below a threshold value or when the fuel rod has already experienced It is controlled to operate below a certain linear power density (called an envelope).

Furthermore, increasing the reactor power above a threshold or envelope is achieved by increasing the core flow rate, and the rate of increase is also limited.

[Purpose of the invention]

An object of the present invention is to provide a method of operating a nuclear reactor that can significantly reduce the probability of fuel rod breakage when the reactor power increases and that allows simple control rod operation.

[Features of the Invention] A feature of the present invention is that the control rods are withdrawn in the power range below the threshold value of the reactor after waiting for the accumulation of Zenon by adjusting the core flow rate to increase the reactor power and subsequently reduce the reactor power. A first control is performed in which a predetermined amount of control rods are inserted in the center of the core, and a plurality of control rods are inserted further in the periphery of the core surrounding the center than the control rod that is inserted the most in the center of the core. A rod insertion pattern is formed, and while the first control rod insertion pattern is maintained, the reactor power is increased by increasing the reactor core flow rate, and the reactor power is decreased by decreasing the reactor core flow rate. After the drop in the number of control rods, a second control rod insertion pattern is formed in which all the control rods around the core are pulled out from the first control rod insertion pattern, and the core flow rate is increased while maintaining the second control rod insertion pattern to reduce the number of atoms. The purpose is to increase the furnace output to a set level.

[Embodiments of the invention]

A preferred embodiment of the present invention has an electrical output of 784 MW,
Power density 51kW/, threshold for control rod withdrawal operation 11kW/ft, output increase rate limit 0.06kW/ft/
The case of BWR of h will be explained.

Control rod pattern at representative points in time (1/4 of core)
is shown in Figure 1. Thermal power of the reactor (reactor power)
Figure 2 shows the reactor power increase locus at reactor startup, with the core flow rate and core flow rate as the coordinate axes. In FIG. 1, the numbers shown at the control rod positions indicate the rate of control rod withdrawal, with 0 indicating full insertion of the control rod and 48 or a blank space indicating full withdrawal of the control rod. The control rod withdrawal operation will be performed in three steps. 1st
The second time, the control rods are withdrawn as much as possible under the threshold of 11kW/ft at the minimum core flow rate (40% of the rated value).
The control rod pattern (73% pattern) at the time when this withdrawal operation is completed (at the point in Figure 2) is the first
Shown in Figure a. With this control rod pattern, the core flow rate is increased to the rated value (100%) while keeping the linear power density increase rate at the limit value of 0.06 kW/ft/h (point 1 in Figure 2). In FIG. 2, solid lines indicate control rod operation, and broken lines indicate core flow rate control. The core flow rate is again set to the minimum core flow rate, the reactor power is rapidly reduced, and after waiting for Zenon to increase, the control rod pattern is changed to the control rod pattern shown in FIG. 1b. The characteristic of this control rod pattern is that in the center of the core, the control rod pattern is the same as the rated pattern (control rod pattern to obtain the reactor output at the rated time, which is a predetermined level), and in the periphery of the core, the control rods are fully inserted. It's because I'm getting used to it. That is, Fig. 1b
Compared to the control rod pattern in Figure 1a and the control rod pattern (rated pattern) in Figure 1c, which will be described later, the control rod pattern shown in Figure 1A has control rods placed around the core inserted into the core, and The control rods arranged at the periphery are inserted deeper than the most inserted control rod in the rated pattern at the center of the core (the control rod numbered 14 in FIG. 1b). The reactor power level decreases due to both the accumulation of Zenon and the operation of control rods deeper into the periphery of the core than the control rods that are inserted furthest in the rated pattern in the center of the core. Even if the control rod pattern shown in Fig. 1b is used, which is the control rod pattern shown in Fig. 1a, which is pulled out from the control rod pattern shown in Fig. 1a to the rated pattern shown in Fig. 1c, the linear power density remains below the threshold value of 11kW/ft. Become. That is,
Insert multiple control rods in the core periphery deeper than the control rod that is inserted furthest in the core core in the rated pattern (in Figure 1b, the multiple control rods in the core periphery are fully inserted). ), it is possible to maintain the linear power density below the threshold of 11 kW/ft and easily change the control rod pattern in the center of the core to the same control rod pattern as the rated pattern.
This can also be done by simply pulling out all the control rods inserted around the core from the control rod pattern in Figure 1b, as described later.
This leads to obtaining a rated pattern of

When the reactor power increases to the point in Figure 2 with the control rod pattern shown in Figure 1b, the rate of increase is again increased while the control rod pattern is maintained in the state shown in Figure 1b.
Increase the reactor power at a rate of 0.06kW/ft/h (up to point 2 in Figure 2). Thereafter, the reactor power is reduced by rapidly reducing the core flow rate until it reaches its minimum, and all the control rods around the core are withdrawn to obtain the control rod pattern shown in FIG. 1c.
Changing from the control rod pattern shown in Figure 1b to the control rod pattern shown in Figure 1c is as simple as pulling out the control rods inserted into the periphery of the reactor core in the control rod pattern shown in Figure 1b. It can be achieved. At this time, in the center of the core where linear power density tends to increase, the maximum linear power density is 12kW/ft, exceeding the threshold of 11kW/ft, but the linear power density is 16.5, which was the linear power density experienced at point 2. kW/ft (envelope) or less.
Therefore, even with the control rod pattern shown in FIG. 1c, there is significantly less risk of damage to the fuel rods located in the center of the reactor core. On the other hand, the control rods are completely withdrawn in the area around the core, but since the linear power density is originally low in the area around the core, it remains within the threshold. Therefore, the control rods were pulled out to the rated pattern while fully observing the operational restrictions to prevent fuel rod damage. At this time, the reactor output is
The point in Figure 2 has been reached. After that, the rate of increase
If the core flow rate is increased while maintaining 0.06kW/ft/h, 100% (rated) reactor power can be achieved.
During this increase in output, the control rod pattern shown in FIG. 1c is maintained. In this example,
The time required to increase the reactor power to the rated value is approximately
It is the 20th.

Examples in which the control rod pattern at the time of rating is different from the pattern shown in FIG. 1 are shown in FIGS. 3a, b, and c. This example is also applied to BWR. Figure 4 shows operation using the control rod pattern shown in Figure 3.
This figure shows the change in reactor power when the nuclear power output of BWR increases. The control rod pattern in FIG. 3 changes in the order of a, b, and c as the reactor power increases. FIG. 3c shows the control rod pattern when the reactor power reaches its rated power. The control rod pattern shown in FIG. 3b corresponds to the control rod pattern shown in FIG. 1b, in which a plurality of control rods arranged around the core are fully inserted into the core. In this embodiment as well, effects similar to those of the above-mentioned embodiments can be obtained.

FIG. 5 shows the distribution in the height direction of the linear power density of the fuel assembly at the positions indicated by diagonal lines in FIG. This fuel assembly is the fuel assembly with the maximum linear power density in the reactor core. Furthermore, characteristic 2 in FIG.
This is the power distribution, or envelope, when the core flow rate is 100% with the control rod pattern in Figure b. Characteristic 3 in FIG. 5 is the power distribution when the control rods placed around the core are pulled out at the minimum core flow rate to form the rated control rod pattern shown in FIG. 3c. Characteristic 3 exceeds the linear power density threshold, but is below characteristic 2 (envelope), which is the already experienced linear power density, and does not violate the operational restriction conditions for preventing fuel rod damage.

The number of control rods to be inserted into the periphery of the reactor core and their insertion depth are determined so that the reactor power level will be below the threshold value of 11 kW/ft when the control rod pattern shown in FIG. 3b is used. The standard is output density
It is a BWR with an electrical output of 51kW/784MW and a total of 20 control rods inserted. The total number of control rods inserted around the core can be considered to be approximately proportional to the electrical output of the reactor.

The characteristics of the operating method of each of the above-mentioned embodiments are that during the increase in reactor power, the center of the core is set to the rated pattern, and the plurality of control rods placed around the core are inserted the most in the rated pattern of the center of the core. The method is to use a control rod pattern (for example, the control rod pattern shown in FIG. 3b) that is inserted with a larger insertion amount than the control rod insertion amount. As a result, it is now possible to fully comply with the operating restrictions to prevent fuel rod damage, which was difficult for BWRs with high power density (51kW/).

Note that the control rods around the core refer to the control rods at the outermost periphery of the core and the control rods adjacent thereto.

〔Effect of the invention〕

According to the present invention, the probability of fuel rod failure when the reactor power increases is significantly reduced, and the control rod operation during reactor startup is significantly simplified.

[Brief explanation of the drawing]

Figures 1a, b, and c are explanatory diagrams showing control rod patterns with respect to the elapsed time after startup in a BWR operating method that is a preferred embodiment of the present invention, and Figure 2 shows the control rod pattern of Figure 1. Figures 3a, b and c are explanatory diagrams showing control rod patterns in other embodiments of the present invention, and Figure 4 is a diagram showing a nuclear reactor power increase based on the control rod pattern of Figure 3. An explanatory diagram showing the power increase, and FIG. 5 is a characteristic diagram showing the power distribution in the axial direction of the reactor core.

Claims (1)

[Claims] 1. A method of operating a nuclear reactor that controls the output of a nuclear reactor by manipulating control rods inserted into the reactor core and adjusting the core flow rate to increase the reactor output to a set level, which is the final goal. In this step, the reactor power is increased by withdrawing the control rods in a power range below a threshold value of the reactor power at which withdrawal of the control rods is stopped, and then the reactor power is increased and the reactor power is subsequently decreased. The control rods are withdrawn in the power range below the threshold after waiting for Zenon to accumulate due to the core flow rate adjustment, and the control rods are inserted by a predetermined amount in the center of the core, and the control rods are inserted into the core surrounding the center of the core. A first control rod insertion pattern is formed by inserting a plurality of control rods further than the most inserted control rod in the central portion of the reactor core in the peripheral portion, and the first control rod insertion pattern is formed while the first control rod insertion pattern is maintained. The operations of increasing the reactor power by increasing the reactor core flow rate and subsequently decreasing the reactor power by decreasing the core flow rate are performed, and after the reactor power decreases, from the first control rod insertion pattern to the vicinity of the reactor core. forming a second control rod insertion pattern in which all of the control rods in the section are pulled out, and increasing the reactor core flow rate while maintaining the second control rod insertion pattern to raise the reactor power to the set level. A nuclear reactor operating method characterized by: