JPS6256894A - Insert aggregate for spectral transfer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (a) Purpose of the Invention [Field of Industrial Application] This invention aims to increase the reactivity of the reactor core by changing the neutron energy spectrum within the reactor core during operation of the reactor, thereby extending the lifespan of the reactor core. This article relates to an interpolation assembly used in a so-called spectrum transfer nuclear reactor.

[Prior art] As a means for changing the spectrum, for example, Japanese Patent Laid-Open No. 56-1
As shown in 11491, there is a mechanical spectrum transfer method performed by inserting and handling a water exclusion rod that eliminates the coolant in the reactor core, which is also a moderator, or a chemical method performed by changing the mixing ratio of water and heavy water. Spectrum shifting methods have been proposed. In the former mechanical spectrum movement method, a large number of water exclusion rods, which are approximately equal to the total length of the fuel assembly, are moved in the axial direction by a drive device, so the axial movement distance is approximately 4 TIL, which is approximately equal to the core length. For this reason, a water removal rod with a relatively large diameter is used to maintain its mechanical strength, and a large number of drive rods are used to drive the removal of water one by one.

The latter chemical spectral transfer method requires expensive heavy water.

Therefore, in the chemical spectrum transfer method, the cost associated with heavy water is enormous, and even though it is theoretically possible, it is difficult from a practical point of view. Since a large number of drive rods are required for this purpose, the chemical spectrum transfer method still increases the cost, and the water removal rod drive during reactor operation requires a large amount of axial travel distance and There is some concern regarding operational reliability due to the thickness of the water removal rod. For this reason,
If the spectral shift effect can be realized without relying on Equation 6 as described above, the economic benefits would be extremely large.

[Problems that the invention seeks to solve 1) This invention has been made in view of the above-mentioned circumstances, and it solves the problem of low reliability that the conventional technology has, especially: Insertion of water exclusion rods in the mechanical spectrum transfer method complicates the RG5 structure above the core for handling, and furthermore, the structure is unsuitable for handling a large number of water exclusion rod pins (small diameter). The purpose of this invention is to provide a trapping aggregate for spectrum movement that eliminates the constraints on water exclusion effect.

(B) Structure of the Invention [Means for Solving the Problem] Corresponding to this object, the subekite movement internal catch assembly of the present invention is inserted into the control rod guide thimble of the fuel assembly. An inner trap aggregate, the inner trap aggregate comprising:
a hollow tube whose lower end is closed and which is inserted into the control rod guide thimble; a box-shaped gathering portion having an opening at the top and closing the opening with a closing member; one end of each of the hollow tubes; It is characterized by comprising a branch pipe line communicating with the gathering part.

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

FIG. 1 is a side view of a spectral shifting interpolator assembly 1 according to an embodiment of the present invention, and is shown partially in cross section and in 1 no. for ease of understanding. In the same figure, reference numeral 2 indicates a hollow tube for spectrum movement. has a rounded taper.

Reference numeral 4 is a box-shaped gathering part, and the gathering part 4 has an opening 3 at the top.
However, this opening 3 is airtightly closed by a closing member 5. The upper ends of the plurality of hollow tubes 2 are connected to and connected to the gathering part 4 through a branch pipe line 6. Therefore, the internal space of each hollow tube 2 and the internal space of the gathering part 4 are communicated through the branch pipe line 6, and these internal spaces are airtight sealed spaces completely isolated from the external atmosphere (however, there is no airtight space inside). is filled with air or a gas such as helium.).

The material of the closing member 5 is not specified, but it may be made of a material that can maintain the -(f4) resistance under the operating environment of the nuclear reactor. The opening 3 is sealed by target or metallurgical bonding.

Note that since the hollow tube 2 remains inserted into the reactor core (fuel assembly) during operation of the nuclear reactor, a silica (carp) tube, which absorbs less neutrons, is used.

Next, how to use this spectrum moving inner bucket assembly will be explained.

The internal trap assembly 1 for movement of spectra 1 to 1 is placed in advance within a fuel assembly before the start of operation of the nuclear reactor.

For example, FIG. 2 shows an example of a cross-sectional view of a fuel assembly showing the distribution of control rod guide thimble in the fuel assembly. is used with its hollow tube 20 inserted into the control rod guide thimble 22 of the fuel assembly 20. <
(During nuclear reactor operation, axial movement is not performed due to hollow tube withdrawal or illness.) In other words, in the example of the fuel assembly shown in FIG. 2, 16 control rod guide thimbles 22 are arranged; Equipped with wooden hollow tubes
Each hollow tube 2 of the internal catch assembly for moving the The disposed closing member 5 is located at the center of the fuel assembly 6 Although only a portion of the fuel rod 21 is shown in FIG. 2 to simplify the drawing, normally the fuel rod 21 and the control rod guide Thimble 22 is positioned within fuel support frame 23 by spacing wires or grid strips, not shown.

Figure 3 is a partial cross-sectional view of a pressurized water reactor for explaining the usage situation of the water pump inside the reactor.
8 is the core of the nuclear reactor, 24 is the pressure vessel, 2
5 is a pressure vessel lid, 26 is a core upper support plate, 27 is
3 is a drive shaft, and 30 is a drive device. As shown in the figure, among the many fuel assemblies 20 arranged in the core 28, the fuel assembly into which the interpolation assembly for spectrum transfer is inserted (the fuel assembly R1 in which the interpolation assembly for spectrum transfer is not inserted is Each control rod guide thimble is used for inserting the control rods), and a hollow tube 2 of the internal material assembly for moving the subaxle is inserted into the control rod guide thimble (the control rod guide thimble is used for inserting the control rods). Therefore, only one hollow tube 2 is shown, but in reality there are several.)

Since the upper end of the fuel assembly 20 is held down by the upper core plate 29, when the coolant in the reactor vessel is introduced into the spectrum shifting insert assembly inserted into the fuel assembly 20, the spectrum The closing member 5 at the top of the moving inner silk material assembly is moved in the axial direction of the drive shaft 27 by the drive device 30, so that the closing member 5 is moved to a sharp protrusion 18 provided at the tip of the drive shaft.
This can be achieved by breaking through it or by tearing it off with a hanger 19.

In this way, at the beginning of reactor operation, the spectrum shifting interpolator assembly, which has a sealed space filled with air or gas such as helium, is used as a blocking member after the middle of the core life when spectrum shifting is required. By breaking 5 and introducing a coolant into the reactor core, the neutron energy magnitude in the reactor core is changed, the reactivity of the reactor core is increased, and the life of the reactor core is extended.

FIG. 4 shows an example of how to break the closing member, and (a) shows an example of how to break the closing member 5. As described above, FIG. The method of breaking through, (b) is a hanging tool 1 in which a tension handle 17 is fixed to the upper surface of the blocking member 5, and this tension handle is provided on the drive shaft.
9 to peel off the tension closure member 5. In addition, in (C), the blocking member 5 is formed of a metal that melts at high heat, and the blocking is released by melting this metal lid with an electric heating element 15 provided at the tip of the drive shaft. method can also be adopted.

[Function] Insertion and handling of water exclusion rod (mechanical spectrum transfer method)
Compared to the case where a moving distance of about 4 m is required, that is, the length of the reactor core, the interpolant assembly for spectral movement of the present invention only needs to have a moving distance of just enough to break the blocking member.
Therefore, the axial movement distance of the eight drive axes is only about 10 cm at most. In addition, the hollow tubes inserted into the control rod guide thimble of the fuel assembly do not move in the axial direction unlike the mechanical spectrum movement method, so even those with a small diameter can maintain their integrity. can be placed. Hit,
More spectrum transfer effects can be expected, and more fuel cost savings can be achieved. For example, FIG. 7 shows an example of how the critical borine concentration changes depending on the burnup. As an example, the one shown by the broken line 11 is an example of a conventional reactor core. During the period shown on the horizontal axis of the figure, air or gas is filled in the hollow tube 2, and the water-to-fuel ratio is kept small.

During period B, the closing member 5 is broken and the coolant is introduced inside, so the water-to-fuel ratio increases and the reactivity can be increased. Therefore, the code 12 is better than the code 11.
It is said that the burn-up can be maintained for a longer time and the fuel cycle cost can be reduced.

(c) Effects of the Invention According to the present invention, it is possible to impart a significant spectrum shifting effect without using complicated mechanical means, so not only can fuel cycle costs be reduced, but also spectrum shifting is possible with a simple device. This method does not require a complex superstructure of the reactor core unlike the mechanical spectrum shifting method, and is therefore advantageous in both reliability and construction cost reduction, such as reducing the overall height of the pressure vessel and simplifying the drive device for spectrum shifting. It is possible to obtain a set of interpolants for spectral shifting.

[Other Embodiments] FIGS. 5 and 6 show a system for facilitating the outflow of air or gas in the hollow tube 2 and the inflow of coolant when the blocking member is broken in the nuclear reactor. This shows an interpolant assembly for spectrum movement with a double flow path inside. Fig. 5 is a top view of the same (however, the collecting part and the hollow tube part are shown in cross section to clarify the internal situation), and Fig. 6 is a sectional view taken along line A-A in Fig. 5. It is. Further, in FIG. 5, the imaginary line shows the outline of the fuel assembly 20 when the spec 1-transfer delivery item assembly is inserted into the fuel assembly.

In FIGS. 5 and 6, reference numeral 7 denotes an annular partition plate provided near the lower end of the gathering portion 4, and the partition plate 7 is provided with a coolant inlet 9 corresponding to the branch pipe line 6. ing. Reference numeral 8 denotes an intermediate partition that starts near the opening 3 of the collecting portion 4 (the figure shows a state in which the closing member 5 is not attached) and extends to the vicinity of the lower end closing portion of the hollow tube 2. The interior is divided into two flow paths 10a and 10b.

In this way, when the interior is divided by the partitions 8, when the coolant flows in through the broken opening 3 of the closing member, the coolant flows through one of the channels partitioned by the partitions 8, as shown by the arrow in the figure. 10a1. :N people, and gas such as air or helium in the interpolant assembly for spectrum movement is connected to the flow path 10.
It is forced to the outside via b, allowing rapid inflow of coolant.

[Brief explanation of the drawing]

FIG. 1 is a side view including a partial cross section of a spectrum shifting interpolator assembly according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a fuel assembly, and FIG. 3 is a cross-sectional view of a pressurized water reactor. Partial cross section,
Figure 4 is a diagram showing an example of how to tear the r111 member, Figure 5
The figure is a top view including a partial cross section of a spectrum shifting interpolator assembly according to another embodiment, and FIG.
The hem section sectional view and FIG. 7 are diagrams showing examples of changes in critical boron concentration depending on burnup. 1... Interpolate assembly for spectrum movement 2... Hollow tube 3... Opening 4... Gathering part 5...
Closing member 6... Branch pipe line 7... Annular partition plate 8... Middle partition 9... Inflow port 10a, 1
0b...Flow path patent applicant Mitsubishi Atomic Crab Industry Co., Ltd. Representative Patent Attorney Osamu Kawai Figure 1 Figure 2 and + 4 2Z Co No. 3
Figure 6 Figure 7

Claims (3)

[Claims] (1) An insert assembly to be inserted into a control rod guide thimble of a fuel assembly, wherein the insert assembly is hollow with a closed lower end and inserted into the control rod guide thimble. It is characterized by being composed of a tube, a box-shaped gathering part having an opening at the top and closing the opening with a closing member, and a branch pipe line communicating the upper end of each hollow tube with the gathering part. An interpolant collection for spectral movement. (2) The spectrum shifting insert assembly according to claim 1, wherein the closing member is a metal lid with a pull handle on the upper surface or a thin metal plate. (3) The hollow tube has a flow path defined by a partition that starts near the opening of the collecting section and extends to near the closed end of the hollow tube's lower end. Interpolant collection for spectral transfer as described.