JPS63101793A - Control rod aggregate for fast breeder reactor - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] (Objective of the Invention) (Industrial Application Field) The present invention relates to the i-control rod!1 combination of a fast breeder reactor, and in particular, the present invention relates to the i-control rod! Concerning control rod assemblies for fast breeder reactors.

(Prior art) In general, a fast breeder reactor has a reactor vessel 1 as shown in Fig. 6.
A reactor core 2 is provided therein, and its upper opening is closed with a shielding plug 3.

The reactor vessel 1 is filled with liquid metal sodium 4 as a coolant, and a coolant inlet nozzle 5 is provided at the bottom thereof, and a coolant outlet nozzle 6 is provided at the peripheral wall thereof.

The inside of the reactor vessel 1 is divided into an upper blennium 9 and a lower blennium 10 by a core support 8 that supports the reactor core 2 .

The reactor core 2 is composed of a nuclear fuel assembly 13, a blanket fuel assembly 14, a reflector 15, and a control rod assembly 16. A core upper mechanism 18 is provided in the upper part of the reactor core 2 through the shielding plug 3, and an upper guide pipe 19 and a rectifying tube 20 are provided at the lower end thereof.

A high-pressure blemish 22 that guides the coolant 4 to the core 2 is provided at the bottom of the core 2 . Upper Blenheim 9 above core 2
is provided with an inner cylinder 23, and this inner cylinder 23 is provided with a plurality of flow holes 24.

Reference numeral 25 indicates a dipped plate provided on the lower surface of the shielding plug 3.

FIG. 7 shows the integrated collection rod assembly of the i and lJ control rods, in which a handling head 28 is formed at the upper end of the lower guide tube 27, and a small-diameter entrance nozzle 29 is formed at the lower end.

A protective tube 30 is provided in the lower guide tube 21 so as to be movable up and down, and a large number of absorbent materials 31 are accommodated within the protective tube 30 while being supported by a lattice plate 32 . A lattice temporary press 34 having a coolant jetting hole 33 is provided at the upper part of the storage tube 30, and this lattice temporary press 34 is connected to a control rod drive mechanism (not shown) by a connecting rod 35. A dash ram 3 is installed at the bottom of the protection tube 31.
6 is provided, and a coolant inflow hole 37 is bored in the upper part of this dash ram 36.

A dashpot 38 is provided above the entrance nozzle 29, and a coolant inlet 39 is also provided at the bottom of the dashpot 38. The control rod assembly 16 configured in this way has an entrance nozzle 29
is inserted into a connecting pipe (not shown) of the n-pressure blemish 22 and mounted at a predetermined position.

Figure 8 is υIt! 11 is a sectional view showing the relationship between the 11-bar assembly, the core upper mechanism, and the nuclear fuel assembly, in which an upper guide tube 41 and an arrangement 21! A tube 42 is provided therethrough. Upper guide pipe 41 and rectifier tube 4
2 are provided facing the control rod assembly 16 and nuclear fuel assembly 13 of the reactor core 2, respectively.

A coolant flow port 43 is formed in the support tube plate 40 at an intermediate position where the upper guide tube 41 and the rectifying tube 42 are attached, and a lower part of an instrumentation well 44 is introduced into each of the rectifying tubes 42 .

In the fast breeder reactor configured as described above, the coolant 4 flowing from the coolant inlet nozzle 5 flows from the lower blennium 10 to the entrance nozzle 29 of the control rod assembly 16 via the high pressure blennium 22.

The inflowing coolant passes through the lower guide pipe 27, flows into the protection tube 30 from the coolant inlet 37 above the dash ram 36, and receives heat as it passes between the absorbers 31. The heated coolant 4 passes through the cold fJI material ejection hole 33 of the grid temporary presser 34 and flows out from the upper opening of the lower guide tube 27.

The coolant 4 flowing out from the lower guide pipe 27 is transferred to the upper blemish 9
The coolant flows out of the reactor vessel 1 through the coolant outlet nozzle 6, and the reactor volume V! The coolant is returned to the coolant inlet nozzle 5 through a heat exchanger, a circulation pump, etc. (not shown) provided outside the coolant 41.

(Problems to be Solved by the Invention) In the fast breeder reactor configured as described above, the degree of coolant 4 flowing out from each control rod assembly 16 is not constant. Furthermore, since there is a temperature difference between the control rod assembly 16 and the adjacent nuclear fuel assembly 13, the core upper mechanism 1
The support tube plate 40, the upper guide tube 41, and the rectifier tube 42 provided at the lower end of the tube 8 are affected by the temperature difference between them, resulting in a temperature fluctuation Δφ expressed as ΔT/(T1-72).
will occur.

This temperature fluctuation Δφ is approximately 60% of the temperature difference, and is 1)-(Z
It is of a certain degree. Note that T and T2 are temperatures of the coolant flowing out from the adjacent i/I rod assembly 16 and nuclear fuel assembly 13, and ΔT is a in FIG. 8.

It shows the temperature amplitude at each position between 5 and 5.

In FIG. 8, symbol C indicates the point at which coolants having different temperatures flowing out from the adjacent control rod assembly 16 and nuclear fuel assembly 13 begin to mix. This point C is located between the adjacent control rod assembly 16 and nuclear fuel assembly 13. Further, the reference numeral ``a'' indicates a point above the 0 point on the lower surface of the support tube plate 30, and the symbol ``a'' indicates a point below the 0 point on the upper surface of the nuclear fuel assembly 13 and the control rod assembly 16.

The temperature fluctuation distribution on the line connecting these points a, b, and c is as shown in FIG. That is, temperature fluctuation occurs above the 0 point and is slightly attenuated at point b, but the amount of attenuation is small.

Due to such temperature fluctuations, the lower end portion of the upper core mechanism 18 is subjected to excessive thermal fatigue. In particular, the upper guide tube 41, straightening tube 42, and support tube plate 40 are vulnerable to thermal fatigue due to temperature fluctuations caused by the high temperature coolant heated by the control rod assembly 16 and fuel assembly 13, and cracks may occur. The problem was that it was easy.

The present invention has been made in consideration of the above-mentioned circumstances, and reduces thermal fatigue of the support tube plate, rectifier tube, and upper guide tube portion of the lower end of the core upper structure, thereby reducing thermal fatigue. It is an object of the present invention to provide a control rod assembly for a fast breeder reactor that can prevent cracks from occurring at parts and joints and improve safety.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an upper guide pipe and a rectifier tube at the lower end of the upper core mechanism, respectively, in a control rod assembly and a nuclear fuel assembly loaded in the core of a fast breeder reactor. In the control rod assembly of a fast breeder reactor, the control rod assembly is arranged to face each other from above, and a coolant diffusion device is provided at the upper part of the control rod assembly to diffuse the coolant flowing out from the control rod assembly.

(Function) Since the coolant diffusion device is provided above the control rod assembly, the coolant flowing out from the control rod assembly is diffused, and the coolant flowing out from the adjacent control rod assembly and nuclear fuel assembly has different temperatures. They begin to mix close to the control rod assemblies and nuclear fuel assemblies.

Therefore, since the distance from this mixing point b11 to the support tube sheet, upper guide tube, and rectifier tube of the core upper mechanism is extended, temperature fluctuations at the bottom surface of the support tube sheet are significantly reduced, and the occurrence of cracks due to thermal fatigue is prevented. can increase safety.

(Actual Droplet Example) A first embodiment of a control rod assembly for a fast breeder reactor according to the present invention will be described with reference to FIGS. 1 and 2.

The outline of the fast breeder reactor is the same as that described in FIG. 6, so the explanation will be omitted. FIG. 1 is an enlarged view of a portion where the reactor core 2 and the upper core mechanism 18 face each other, and the reactor core 2 is loaded with a control rod assembly 16 and a nuclear fuel assembly 13 adjacent to each other. The control rod assembly 16 is provided with a protective tube 30 that can be raised and lowered within the lower guide tube 27, and a large number of absorbent materials 31 are placed inside the protective tube 30.
It accommodates. A lattice temporary presser 50 is attached to the upper part of the protective tube 30.
is pulled, and the connecting rod 35 is connected to this grid temporary presser 50.

A plurality of coolant jet holes 51 are bored outwardly in the grid temporary press 50 as a coolant diffusion device, and the coolant 4 passing through these coolant jet holes 51 from below to above is directed outward in the traveling direction. It is designed to change direction. Lower guide pipe 27
and a coolant outlet 52 at the upper end of the nuclear fuel assembly 13.
53 are provided.

On the other hand, an upper guide tube 41 and a rectifier tube 42 are provided on a support tube plate 40 at the lower end of the core upper mechanism 18 to face the control rod assembly 16 and the nuclear fuel assembly 13 of the reactor core 2, respectively. Support tube plate 4 located at an intermediate position between the upper guide tube 41 and the adjustable M cylinder 42
A coolant flow port 43 is formed at 0, and a lower part of an instrumentation well 44 for measuring the flow rate is introduced into the rectifying cylinder 42.

In the control rod assembly of the fast breeder reactor configured as described above, the coolant 4 flowing upward in the lower guide tube 27 is absorbed as it passes between the absorbers 31 housed in the protection tubes 30. Coolant spout hole 51 of grid temporary presser 50 is heated
More gushing.

At this time, since the coolant jetting holes 51 are provided facing outward, the cold Nl material 4 passing through and covering the coolant jetting holes 51 changes its direction outward and diffuses. Then, since the coolant 4 flows out from the coolant outlet 52 while being diffused in a turbulent state, the coolant 4 flowing out from the nuclear fuel assembly 13 starts to mix with the coolant 4 at a position d near the upper end of the lower guide pipe 27.

At this time, since the temperature of the coolant 4 ejected or flowing out is different for each of the f and 13 control rod assemblies 16 and the nuclear fuel assemblies 13, the coolants 4 are mutually adjacent to each other above the point d where the coolants 4 having different temperatures begin to mix. Temperature fluctuation Δφ due to temperature difference in
occurs. This temperature fluctuation Δφ increases the temperature of the coolant flowing out from the adjacent control rod assembly 16 and nuclear fuel assembly 13 to T1. It is expressed as ΔT/(T 2 , T2), where T2 is the temperature range at each position between a and b and ΔT is the temperature imaging width at each position between a and b.

The fruit I shown in Figure 2! A shows the temperature fluctuation distribution between the upper end of the ill tll rod assembly 16 and the support tube sheet 40, and the symbol d is at the lower surface position of the support tube sheet 40.
Indicates the point above the point, a is υ! A point below point d on the upper surface of the rod assembly 16 is shown.

As is clear from FIG. 2, temperature fluctuation Δφ hardly occurs below point d. Then, it reaches a peak at a position slightly above point d, and tends to decrease as it goes above it. Therefore, the lower the point d is, that is, the longer the distance from point d to point b, the more J
The temperature fluctuation Δφ multiplied by 3 will decrease.

Therefore, the coolant ejection holes 5 facing outward in the grid temporary press 50
1 and thereby lowering the point at which coolants 4 of different temperatures begin to mix from the conventional point 0 to point d, the temperature fluctuation Δφ at point b is significantly reduced. As a result, thermal stress at the lower end of the core upper mechanism 18 is reduced, making it difficult for cracks to occur. Note that the curve B indicated by the broken line in FIG.
The figure shows the temperature fluctuation distribution.

Next, a second embodiment of the present invention will be described using FIGS. 3 and 4. In this embodiment, a plurality of coolant ejection holes 51A are provided as a coolant diffusion device in a grid temporary presser 50, which are uniformly inclined in the circumferential direction.

With such a configuration, the coolant ejection holes 51A
The coolant 4 ejected from the fuel cell 4 starts to swirl, flows out from the lower guide pipe 27 and diffuses while swirling, and mixing with the coolant 4 from the nuclear fuel assembly 13 is promoted.

As a result, the coolants 4 having different temperatures begin to mix with each other at a lower position. That is, the position of point d shown in FIGS. 1 and 2 becomes lower. therefore,
Since the temperature fluctuation Δφ in the support tube plate 40 and the like is further reduced, thermal stress is reduced and cracks can be more effectively prevented.

FIG. 5 shows a third practical example of the present invention, in which a spiral fin 55 is provided on a connecting rod connected to a grid temporary presser 50 as a coolant diffusion device. The cooling 04 ejected from the grid temporary presser 34 flows out and diffuses while swirling due to the spiral fins 55, and rapidly begins to mix at the outlet of the lower guide tube 27. Therefore, the same effects as those of the above embodiments can be obtained.

〔Effect of the invention〕

As explained above, the present invention provides a fast breeder reactor in which the control rod assembly and the nuclear fuel assembly loaded in the core of a fast breeder reactor are provided with an upper guide pipe and a rectifier tube at the lower end of the upper core mechanism, respectively, facing each other from above. At the control rod assembly of the reactor, we installed a coolant expansion rllv4v1 at the top of the control rod assembly to diffuse the coolant flowing out from the control rod assembly, so that the coolant spreads around the control rod assembly at the exit of the control rod assembly. The temperature fluctuations around the support tube plate, upper guide tube, and rectifier tube at the lower end of the upper core mechanism can be reduced by lowering the position where coolants of different temperatures begin to mix with each other. Less likely to generate cracks due to thermal fatigue,
This has the effect of improving the safety of nuclear reactors.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the relationship between the control rod assembly, the upper core mechanism, and the nuclear fuel assembly in a first embodiment of the RA til rod assembly for a fast breeder reactor according to the present invention, and FIG. 3 is a front view of the lattice temporary press in the second embodiment of the present invention, FIG. 4 is a plan view of the lattice temporary press in the above embodiment, and FIG. 5 is a diagram of the third embodiment of the present invention. A cross-sectional view showing the relationship between the control rod assembly, the core upper mechanism, and the nuclear fuel assembly in the case of pyogenes, Figure 6 is a cross-sectional view showing the schematic configuration of a fast breeder reactor, and Figure 7 shows a conventional example of the control rod assembly. 8 is a sectional view showing the relationship between a conventional idle till rod assembly, an upper core mechanism, and a nuclear fuel assembly, and FIG. 9 is a conventional warm fluctuation distribution diagram. 4... Coolant, 13... Nuclear fuel assembly, 16...
Control rod assembly, 27... Lower guide tube, 30... Maintenance'
S pipe, 35... Connecting rod, 40... Support tube plate, 41.
... Upper guide pipe, 42 ... Straightening cylinder, 43 ... Coolant distribution port, 44 ... Instrumentation well, 50 ... Grid temporary presser, 51 ... Coolant jet hole (coolant diffusion device), 51A
...Coolant outlet (coolant diffusion device), 52.53・
... Coolant outlet, 55... Fin (coolant diffusion device). Representative Patent Attorneys Nori Chika Ken Yudo Hiroshi Mimata Fumiyo l Go 2 Kodai 3 Figure 4 Figure I6 Figure 5 Tsuri 6 Figure 8

Claims (1)

[Claims] 1. A fast breeder reactor in which an upper guide pipe and a rectifier tube at the lower end of the upper core mechanism are arranged to face each other from above on a control rod assembly and a nuclear fuel assembly loaded in the core of the fast breeder reactor, respectively. A control rod assembly for a fast breeder reactor, characterized in that a coolant diffusion device for diffusing coolant flowing out from within the control rod assembly is provided in the upper part of the control rod assembly. 2. The control rod assembly for a fast breeder reactor according to claim 1, wherein the coolant diffusion device is provided with outward coolant jet holes in the lattice plate retainer of the control rod assembly. 3. The control rod assembly for a fast breeder reactor as set forth in claim 1, wherein the coolant diffusion device is provided with coolant ejection holes that are inclined at a constant angle in the circumferential direction in the lattice plate retainer of the control rod assembly. . 4. The control rod assembly for a fast breeder reactor as claimed in claim 1, wherein the coolant diffusion device is provided with spiral fins on a connecting rod connected to the lattice plate retainer of the control rod assembly.