JPS6050316B2 - Nuclear power plant reactor power distribution control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactor power distribution control method for a nuclear power plant, which controls the reactor feed water temperature and adjusts the power distribution within the reactor in order to perform load following operation of the nuclear power plant.

The proportion of nuclear power plants in the power system is likely to increase rapidly in the future, and as a result, the conventional -4←-c
Z, length, space ± one yu,, 3 no ≠ #゛outμ〉 T = ``1 ηγ and totos, 〉] is occurring.

Taking a boiling water nuclear power plant as an example, if the load following operation described above is carried out using the conventional method, if the load following is rapid, the interaction between the fuel pellets and the cladding material will cause damage to the cladding material. To prevent this, Pre
condition ing Interim Operat
ingMana Friendship Recommendation
ns (abbreviated as PCIOMR) is recommended.

PCIOMR refers to hydrates (
This means operating in an output increasing pattern that does not easily cause damage to the fuel rods such as cracks due to the formation of hydrocarbons or pellet-to-clad interaction. This will be explained in more detail below. In Figure 1, the linear power density is 8kW.
/■, that is, up to point A, which is about 40% of the reactor output, the control rods can be freely withdrawn to increase the output, but beyond that point, the linear power density is O per hour, and the reactor core slows down to less than 6 kW/ft. When the flow rate is increased and reaches point B, which is 100% flow rate, if this state is maintained for one full hour, fuel preconditioning will occur.
g) has been carried out.

In this case, a preconditioning (hereinafter abbreviated as PC) envelope is created at this linear power density. Furthermore, in order to increase the reactor output in step 5, the reactor core flow rate is decreased in the opposite way as before,
Return to point A, pull out the control rod, and increase the reactor output from point A to point C. After that, the core flow rate is slowly increased again, and when it reaches point D, which is 100% flow rate, the target 1
Since the output will be 00%, the furnace output will be maintained for a period of time in this state. Then, a PC envelope is created in this core state. That is, FIG. 1 is a diagram showing a typical output increase pattern of PCIOMR operation. FIG. 2 is a diagram of the PC envelope E created based on the operation described above.

FIG. 3 is a typical example showing changes in output P1 xenone concentration Xe and core flow rate W when daily load following operation is performed according to PCIOMR.

The output P is operated at a constant output as shown in figure a, but for example, at 1C @ in the afternoon at night, the output is lowered as shown in the figure, and at 7 a.m. the next morning, it is returned to the original output. It is assumed that the output is maintained until 1:00 p.m. in the evening and the above-described output change pattern is repeated.

As shown in figure b, the Xe concentration for this output change pattern increases from 1 p.m. on the night when the output is reduced until 7 a.m. the next morning, and decreases after 7 o'clock. As shown in Figure c, the core flow rate W increases at 7 am in the morning compared to the time when the PC envelope was created due to the feedback effect of the Xe concentration.
At 1:00 a.m., several hours have passed, contrary to the phenomenon described above, the core flow rate W
decreases. In the above-mentioned FIG. 2, the axial power distribution at 7:00 a.m. and 1:00 a.m. is shown by a dashed line F and a dotted line G.

At 7 a.m., the core flow rate increases, so the amount of voids generated, in other words, the amount of neutrons leaked, decreases, and the power distribution curve F above the core exceeds the PC envelope E. 1'5
! Until then, the core flow rate decreases, so the amount of voids generated increases and the power distribution curve G below the core exceeds the PC envelope E.

In this way, the output distribution pattern at 7 a.m. and 1:00 a.m. is PC.
It does not match the envelope and is partially broken. The above explanation does not take into account the control of the supply water temperature, so it is expected that the PC envelope created by the conventional method will be broken when performing load following operation, so the transient maximum output distribution will be calculated. It is necessary to create a one-PC envelope (hereinafter referred to as expansion of the PC envelope) that includes this. An object of the present invention is to provide a method for expanding the PC envelope by controlling the reactor power distribution by changing the feed water temperature in advance in order to perform load following operation. The principle of the present invention will be explained below.

If the reactor power P is kept constant and the water supply temperature T to the reactor is made higher (or lower) than a predetermined value, the amount of voids generated in the reactor core will increase (or decrease); If the flow rate is constant, the reactor power decreases (or increases), so the core flow rate is increased (or decreased). Along with this, the in-core power and distribution increases above the core (
(or decrease) and decrease (or increase) below the core. By utilizing this characteristic, when performing load following operation, it becomes possible to further shift the created PC envelope to a desired value, and it is possible to easily satisfy the restrictive conditions for operation under the PC envelope. can. 1st above
At point D of 100% output shown in the figure, by gradually increasing the feed water temperature T, the reactor power distribution is gradually expanded above the core. Conversely, by lowering the feed water temperature T, the reactor power distribution is expanded below the core. Furthermore, by increasing (or lowering) the feed water temperature at point C or between C and D, the core flow rate can be slowly increased. This makes it possible to expand the PC envelope for the same reason as mentioned above.The following means can be considered to expand the PC envelope created by PCIOMR operation by controlling the feed water temperature.

(a) To expand the PC envelope in the upper part of the core, the feed water temperature is increased according to the expansion width.

(b) To expand the PC envelope in the lower part of the core, lower the feed water temperature according to the expansion width. A method of controlling the supply water temperature will be explained using FIG. 5. In the figure, a plurality of control rods 3 are inserted into a core 2 of a nuclear reactor 1.

In addition to inserting and withdrawing control rods, the reactor output is controlled by driving a jet pump 5 inside the reactor using a recirculation pump 4 installed outside the reactor to forcefully circulate coolant inside the reactor core 2. This is done by The coolant sent out by the jet pump 5 is heated and becomes steam while rising from below the core 2.

``This steam passes through a steam/water separator 6 to separate moisture.
The dry steam is guided to the turbine 7, where it is converted into rotational energy of the turbine, and turned into electrical energy by a generator 8 connected to the turbine, which is then transmitted to the power system and used. The steam that has undergone mechanical work in the turbine 7 is then cooled in a condenser 9 to become condensate, and is then transferred to a feed water heater 11 by a condensate pump 10.
sent to. Feedwater heater 11 extracts a portion of the steam flowing through turbine 7 and is heated by the steam sent through bleed valve 12 . The feed water whose condensate temperature has been raised using the air extracted from the turbine as a heating medium is supplied into the reactor 1 by the feed water pump 13 . Therefore, in order to control the feed water temperature, the feed water temperature setting value is sent from the operation control panel 14 to the feed water temperature control device 15, where it is converted into a feed water temperature control signal, and the extraction valve that controls the steam extracted from the steam turbine is activated. Control opening degree. FIG. 4 is a diagram in which the PC envelope is expanded by the above-described means.

A solid line H in the figure shows the axial average power distribution created by conventional PCIOMR operation.

The core state at this time is that the reactor power is 100% rated, the core flow rate is 89%, and the core inlet enthalpy is 289Kca1/K.
It is 9. On the other hand, broken line 1 indicates that the reactor power is 100% and the core flow rate is 9.
8%, and the core inlet enthalpy was 293 Kca1/Kg, which is the result of increasing the feed water temperature. It can be seen from this that the PC envelope is expanded above the core. As explained in detail above, according to the present invention, when load following operation is performed in a boiling water nuclear power plant, the PC envelope is expanded, and the operation is possible within the expanded range, thereby ensuring the integrity of the fuel. The benefits of ensuring this are significant.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a typical pattern of PCIOMR operation,
Figure 2 is a diagram showing the PC envelope and axial average furnace power distribution in load following operation, Figure 3 is a diagram showing time changes in output, Zenone concentration, and flow rate in daily load following operation, and Figure 4
The figure shows the results of reactor power distribution control using the method of the present invention;
FIG. 5 is a block diagram of a control system according to the present invention.

Claims (1)

[Claims] 1. In a method for controlling the reactor power distribution in order to prevent damage to the cladding material due to fuel pellet-to-cladding interaction, when the power distribution above the reactor core is further increased, the power supply to the reactor core is When increasing the feed water temperature and increasing the power distribution below the reactor core, it is recommended to lower the feed water temperature, control the reactor power distribution, and adjust the fuel to withstand subsequent rapid changes in power. Characteristics of nuclear power plant reactor power distribution control method. 2. A reactor power distribution control method for a nuclear power plant according to claim 1, characterized in that the power distribution is changed by gradually changing the feed water temperature. 3. The power distribution control method for a nuclear power plant according to claim 1, characterized by changing the feed water temperature, gradually increasing the core flow rate, and changing the power distribution.