JPS5912156B2 - Fuel loading method for boiling water reactors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel loading method for a boiling water reactor that averages the burnup of each fuel rod and flattens the power distribution at all times.

Replacement cores for conventional boiling water reactors often employ a scatter loading method that distributes new fuel almost uniformly throughout the core.

In this system, the four fuel bundles placed adjacent to the control rods (called control rod cells) each belong to a separate replacement fuel group with a different irradiance, and the four fuel bundles in each control rod cell The average burnup of the fuel bundle is maintained at a nearly uniform value, flattening the power output throughout the cycle, and requiring fewer fuel transfer operations.

Examples of this method are shown in Figures 1.2 and 3.

Figure 1 shows the state before irradiation during the initial cycle, and the fuel bundles are from 0, 1, 2, and 3 cycles of irradiation history1.2
, 3.4, and the average core burnup after one cycle of irradiation is 5GWD/ST, but the fuel bundle after the ■ cycle is unirradiated fuel (0.0GWD/5T) l-
+21 cycle irradiated fuel (5,0GWD/5T) 2-
) 32-cycle irradiated fuel (10,0GWD/5T) 3
-+43 cycle irradiated fuel (15,OGwp/5T)
Changes to 4-+D (discarded) (Figure 2).

Then, the discarded fuel bundle D is replaced with a new fuel bundle 1.

In this way, new fuel is sequentially supplied and circulated for each cycle.

On the other hand, the intangible arrangement of control rods inserted into the reactor core during reactor operation is shown in Figure 3 A1. A2, B1. There are 4 types of B2.

In the figure, X marks indicate cells into which control rods are inserted among the control rod cells arranged in a grid.

If these four types of arrangement are collectively shown as shown in FIG. 3C, if each type is used the same number of times, the control rods will be uniformly inserted into every control rod cell in the central region.

In this way, by repeatedly using the above four types of control rod arrangement in the scatter loading system, the fuel burnup distribution is averaged and the output can be flattened.

However, on the other hand, the rearrangement of these four types of control rods
This is also a major drawback of the conventional method.

Not only is the operation of pulling out a control rod and inserting it in a different position complicated, but the loss of symmetry in the control rod arrangement during conversion can cause large distortions and fluctuations in the output distribution.
This is because it may result in damage to the fuel rods.

Therefore, the method of the present invention provides a fuel loading method that can improve the integrity of the fuel and flatten the power distribution without changing the control rod insertion position.

The method will be explained in detail below in FIG.

The control rods will be loaded using the scatter method.

Therefore, the control rods are arranged every other vertically, horizontally, and diagonally in the lattice-like arrangement of the control rod cells, and are arranged symmetrically from the center of the reactor core in the vertical, horizontal, and diagonal directions. be fixedly provided.

For example, the above-mentioned FIG. 3 A1. Make it similar to the A2 arrangement, and do not change this arrangement.

An example is the position surrounded by a square in FIG.

Therefore, the initial fuel bundle is arranged with burnup as follows.

In the control rod cell into which the control rod is inserted, al---
-...O,OGWD/ST a,...5. QQWD/5T a3---10. OGWD/ST a4-----・-16, OGWD/ST In the control rod cell where no control rod is inserted, bl...
...0.0GWD/5T b2...4.0GWD/5T b3...10. OGWD/S Tb4...
...14. OGWD/ST The reactor is operated in this way, and the core average burnup is approximately 5.0.
At the end of QWD/ST combustion (1 cycle), the 5th
As shown in the diagram.

That is, Fig. 4 al (0,0GWD/ST) → Fig. 5 a
'2 (4, OGWD/8T) Figure 4 a2 (6,0GWD
/ST) → Fig. 5 a'3 (8, OGWn/sT) Fig. 4 a3 (10,0GWD/5T) - + Fig. 5 a'4 (1
4, OGWD/ST) Figure 4 a4 (14, oGWD//
sT)→Fig. 5d (20, OGWD/ST).

Also, Fig. 4 b1 (0,0GWD/5T) - + Fig. 5 b'
, (6,0GWD/ST) Fig. 4 b2 (4,0GWD/ST)
ST) → Figure 5 b'3 (to, OGWD/ST) Figure 4 b3 (1o, o GWD/ST) → Figure 5 b', (16
, OGWD/8T) Fig. 4 b4 (14, o GWD/S
T) → change to Figure 5 d (20,0GWD/fly).

When the lifespan of d and d has ended, they are disposed of and replaced with new fuel (Figure 6).

However, at the same time (as shown in FIG. 7), the fuel bundle a'2 t a'3t a'4 adjacent to the control rod
The fuel bundle b'2 t b that was not adjacent to the control rod
Exchange with '3t b'4.

This exchange is b'! , b'3. b'4 is performed not from one control rod cell but from three control rod cells.

(In this case, simply exchanging a'2 and b'2 is effective.

a/3t a'41 b'3 j t (For 4, the combustion has progressed sufficiently and the amount of fissile material has decreased, so a large output cannot be expected, so there is no need to pay much attention to it.) .

When one cycle of irradiation is completed in this way, new fuel is replenished and the fuel bundle of the control rod cell that is in contact with the control rod is replaced again with a fuel bundle that has not been in contact with the control rod and has undergone the same irradiation cycle.

By repeating this exchange, each fuel bundle will be adjacent to the control rod destined for one cycle, with each cycle being four cycles.

This is similar to the conventional method of inserting control rods into each fuel bundle once by repeating four different patterns.

The effects of this arrangement on output will be described below.

FIG. 8 shows the arrangement relationship between control rods and fuel bundles.

Table 1 shows the results of calculations using the three-group two-dimensional diffusion code for the power distribution of the fuel rods with and without the control rods inserted in this shape.

A indicates when the control rod is present, B indicates when there is no control rod.

Comparing the fuel rod outputs at the (ltl) positions of A and B, A...0.41B...1.20
It can be seen that when the control rods are inserted, the output is kept low, and the fissile material is consumed less and remains burnt.

Next, Table 2 A t B shows the case where the control rod is continuously inserted and withdrawn up to 10QWD/ST, and the case where the control rod is continuously inserted and withdrawn until 10GWD/ST.
This is a calculation of the power distribution if the control rod continues to be withdrawn until

The output of the fuel rod at the same <(1-1) position is A...
1,36B...1.07.

Therefore, if the control rods are fixedly arranged and operated, the maximum output in the fuel bundle will appear at the fuel rod at the (1-1) position and can reach as much as 1.36. It shows.

Further, Tables A and B in Table 3 similarly compare power distributions with and without control rods up to 50WD/ST.

The fuel rod output at position (1-1) at A is 1.26,
The power distribution when the control rod is pulled out and burned to 10 QW D/ST is as shown in Table 4 (1
-1) The fuel rod output will be 1.15.

It can be seen that it is significantly lower than 1 and 36 shown in Table 2 above.

That is, by appropriately distributing the insertion and withdrawal of control rods, local increases in the output of the fuel rods are suppressed and the output distribution is flattened.

However, the method of the present invention fixes the control rod installation position, eliminates the complexity of control rod operation, simplifies fuel exchange, and ensures the soundness of the fuel as described above, resulting in power distribution. This is a unique method of fuel loading for boiling reactors that aims to flatten the surface area.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the fuel loading arrangement in a conventional core at the initial stage of combustion, Figure 2 is an explanatory diagram of the final stage of combustion, Figure 3 is a pattern diagram showing the intangible arrangement of control rods, Figure 4 is an explanatory diagram of the state of the fuel loading arrangement at the beginning of combustion in this cycle to explain an embodiment of the present invention, Figure 5 is an explanatory diagram of the state at the end of combustion, and Figure 6 is the state in the middle of transition to the next cycle. Explanatory diagram,
FIG. 7 is an explanatory diagram of the state at the initial stage of homogeneous cycle combustion, and FIG. 8 is an enlarged cross-sectional view of the control rod cell, illustrating the relationship between the fuel bundle and the control rods.

Claims (1)

[Claims] In a reactor core in which 14 fuel bundles are arranged in a square and a control rod cell into which a cross-shaped control rod can be inserted is one unit, and these control rod cells are arranged in a grid, Control rods are set at positions corresponding to the centers of control rod cells that are arranged every other vertically, horizontally, and diagonally and are symmetrical vertically, horizontally, and diagonally from the center of the reactor core.゜2. A control rod cell in which the irradiated fuel bundle of 3 cycles is arranged and the control rod is inserted in each cycle while observing the principle of replacing the 4-cycle irradiated fuel bundle with a new fuel bundle every cycle. A fuel bundle for a boiling water reactor, characterized in that a fuel bundle of the same irradiation cycle that belongs to a control rod cell in which no control rod is inserted and has the same irradiation cycle history and that has never been adjacent to a control rod is replaced. Loading method.