JPH049480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control rod assembly for controlling the output of a nuclear reactor suitable for a fast breeder reactor (FBR).

[Technical Background of the Invention] A control rod assembly accommodates a control rod body containing a neutron absorbing material in a guide tube so as to be able to move up and down, and controls the output of the reactor core by inserting and removing the neutron absorbing material into the core region. It is something. By the way, control rods generate heat when they absorb neutrons, so a coolant flows through them to remove the heat. Note that the coolant flows within the control rod body and through the gap between the guide tube and the control rod body as a flow path.

That is, as shown in FIG. 1, a control rod main body 2 is suspended within a cylindrical guide tube 1 by an extension rod 3. As shown in FIG.

A handling head 4 is formed at the upper end of the guide tube 1, and an entrance nozzle 6 is attached to the lower end. A coolant inlet 7 and an outlet 8 are formed in the entrance nozzle 6, and a dash pot 9 is provided at the upper end thereof. A dart ram 10 provided at the lower end of the control rod body is inserted into and removed from the dart pot 9.

A coolant inlet 11 is provided at the lower end of the control rod main body 2, and a control rod element 12 containing a built-in neutron absorber is bundled inside the main body 2, and a pair of stators 13, 14 are provided at both upper and lower ends of the control rod element 12. Supported by.

In addition, a coolant outlet 1 is provided at the upper end of the control rod body 2.
5 is provided. Note that a grip portion 16 is attached to the upper end of the extension rod 3.

The control rod assembly having the above configuration is loaded on a core support plate 17 (not shown).

[Problems with Background Art] The amount of heat generated by control rods varies greatly depending on the insertion position in the reactor core, and the smaller the insertion amount of the control rod, the smaller the amount of heat generated, so the coolant temperature becomes considerably lower than the fuel outlet temperature. Furthermore, the coolant flowing through the gap between the control rod body 2 and the guide tube 1 as a flow path does not contribute to heat removal, so the coolant temperature is further lowered. Therefore, the coolant at a lower temperature from the control rod outlet and the coolant at a higher temperature from the fuel outlet alternately reach the core upper structure, particularly the rectifier.

This causes high-cycle thermal fatigue in the upper core mechanism.

This phenomenon is called thermal striping.

Due to this thermal striping, the structural material of the upper core mechanism, which is made of stainless steel (SUS304), cannot maintain its integrity over the entire life of the reactor. In the current core design, the integrity of the core is maintained by making the upper core mechanism from high-strength steel (INCONEL718).

However, high-strength steel is about 10 times stronger than stainless steel.
It is twice as expensive, making nuclear reactors very expensive.

[Objective of the Invention] This invention was made based on the above circumstances, and provides a control rod assembly that can prevent a decrease in coolant temperature when the amount of control rods inserted into the reactor core is reduced and the amount of heat generated is reduced. It is an attempt to provide the body.

[Summary of the Invention] The present invention comprises a guide tube installed in a reactor core through which coolant flows upward and has a handling head at the top and an entrance nozzle at the bottom; an extension rod having a gripping portion; a control rod body connected to the lower end of the extension rod and incorporating a neutron absorbing material; a large diameter portion formed on the extension rod; a flow passage restrictor whose diameter part is pulled up to adjust the flow rate of the coolant inserted therein; and a cooling device which is removably placed on the upper end of the control rod body and is formed between the body and the inner surface of the guide tube. This is a control rod assembly characterized by comprising a flow rate regulator that can sandwich the cross-sectional area of the flow path of the material.

[Embodiments of the Invention] Hereinafter, a first embodiment of a control rod assembly according to the present invention will be described with reference to FIGS. 2 and 3. That is, as shown in FIG. 2, a control rod body 2 is suspended within a cylindrical guide tube 1 by an extension rod 3. As shown in FIG. A handling head 4 is formed at the upper end of the guide tube 1, and an entrance nozzle 6 is attached to the lower end. A coolant inlet 7 and an outlet 8 are formed in the entrance nozzle 6, and a dash pot 9 is provided at the upper end thereof. A dart ram 10 provided at the lower end of the control rod body is inserted into and removed from the dart pot 9.

A coolant inlet 11 is provided on the lower surface of the control rod body 2, and a control rod element 12 containing a built-in neutron absorber is bundled inside the body 2, and both upper and lower ends of the element 12 are connected to stators 13 and 14. It has been well supported.

In addition, a coolant outlet 1 is provided at the upper end of the control rod body 2.
5 is provided. Note that a grip portion 16 is attached to the upper end of the extension rod 3.

Further, a large diameter portion 18 is provided between the upper end surface of the protection tube 5 and the gripping portion.

A flow path restrictor 19 is provided at the upper part of the guide tube, and a flow path hole 20 is formed in the flow path restrictor. A flow rate regulator 2 is detachably attached to the upper end of the protection tube 5.
1 is placed. The flow rate regulator 21 is provided with a coolant passage hole 22 . Furthermore, curved surfaces 23 are formed on the upper and lower edges of the flow rate regulator. A small gap 24 is formed between the flow rate regulator 21 and the guide tube 1, allowing the coolant to flow slightly. When the control rod main body 2 suddenly falls, the flow rate regulator 21 follows this and gradually descends.

Here, when the extension rod 3 is pulled up by a certain stroke, the large diameter portion 18 moves into the flow path hole 2 of the flow path restrictor 19.
0 and narrow the coolant flow path at a certain rate.

FIG. 3 shows the coolant flow rate and coolant outlet temperature from full insertion to full withdrawal of the control rod.

Line a shows the striping control temperature. This was determined based on the condition that striping is alleviated if the temperature difference between the fuel outlet temperature and the control rod outlet is within a certain value. Since the fuel outlet temperature is low when fully inserted and high when fully withdrawn, this straight line a is an upward-sloping straight line to the right. Furthermore, line b shows the exit temperature of the conventional control rod. Line c is the conventional coolant flow rate.
As shown, since the coolant flow rate is constant over the entire stroke, it is shown that when the control outlet temperature of line b is pulled out beyond a certain stroke, it falls below the striping limit condition.

Here, when the flow rate regulator 21 is introduced as in the present invention, the protective tube-guide tube gap flow rate is reduced. Line d is the coolant flow rate of the present invention, and line e is the control rod exit temperature of the present invention.

First, by providing the flow regulator 21, the flow rate of coolant passing through the coolant flow section 25 formed between the control rod body 2 and the guide tube 1 is reduced, and the outlet temperature is increased as shown by the line e. can be made higher.

In addition, in response to a decrease in the control rod outlet temperature due to a decrease in heat generation due to the withdrawal of the control rod, the large diameter portion 18 of the extension rod 3 and the flow passage restrictor 19 are activated, as shown by line d. The coolant flow rate is further reduced to raise the coolant temperature as shown by line e. However, the lever flow rate regulator 21 and the flow path restrictor 1
The combination of the two items 9 allows the coolant temperature to exceed the striping limit temperature over the entire stroke.

Therefore, according to the present invention, striping on the upper core mechanism can be reduced, the integrity of the upper core mechanism can be maintained, and furthermore, it is not necessary to use high tensile strength steel, so the reactor can be manufactured at low cost. I can do it.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 to 6.

In addition, in the figure, the same parts as in FIG. 2 are indicated by the same reference numerals, and the explanation of the overlapping parts will be omitted.

The embodiment shown in FIG. 4 differs from that shown in FIG. That is, as shown in FIG. 5, which shows part A in FIG. 4 enlarged, the flow path restrictor 26
A plurality of small protrusions 29 are formed at a predetermined interval 28 on the inner surface of the circular tube portion 27, and the small protrusions 29
A spacing member 31 having a large diameter hole 30 is attached to the spacer. An annular plate 33 having a channel hole 32 is inserted into the interval 28 . The annular plate 33 is sandwiched between the spacing members 31 from above and below, and the outer diameter of the annular plate 33 is larger than the inner diameter of the spacing member 31 to prevent the flow of coolant between the inner surface of the annular plate 33 and the outer surface of the extension rod 3. form a road.

Therefore, in the second embodiment, the large diameter portion 1 of the extension member 3 is
8 is inserted, the annular plate 33 can move horizontally and become eccentric.

Next, the operation of the second embodiment will be explained. As shown in FIG. 6, when the diameter portion 18 of the extension rod B reaches the annular plate 33, the flow path between the outer periphery of the extension rod 3 and the inner periphery of the annular plate 33 is sandwiched.

Next, when the upper guide tube 34 is eccentric as shown by the broken line 44 and the control rod is eccentric, the annular plate 3
3 contacts the extension rod 3 vertically with the spacing member 31 as an axis, moves horizontally, and becomes eccentric. Further, even if the annular plate 33 is eccentric as described above, no flow path is formed between the inner periphery of the spacing member 31 and the outer periphery of the annular plate 33. The flow path between the outer periphery of the extension rod 3 and the inner periphery of the annular plate 33 narrows when the large diameter portion 18 of the extension rod 3 reaches the annular plate 33, so when the amount of control rods inserted into the reactor core decreases, the control rod The flow of coolant to is reduced.

Furthermore, the amount of eccentricity of the control rod can be increased compared to the flow path restriction of the first embodiment shown in FIG. 2 without changing the cross-sectional area of the flow path in the portion where the flow rate is narrowed. .

This second embodiment allows for a large allowable eccentricity and allows complete insertion even during earthquakes and core curvature, leading to improved reliability of the nuclear reactor.

Next, a third embodiment of the present invention will be explained with reference to FIG. In the figure, the same parts as those in the embodiment shown in FIGS. 2 and 4 are given the same reference numerals, and the explanation of the overlapping parts will be omitted. In FIG. 7, reference numeral 35 denotes an annular support having a pair of protrusions 36 protruding from both ends of the inner surface, and a pipe 37 is inserted between the protrusions 36 of this annular support 35. A flow path restriction 38 is formed by this. The inner diameter of the pipe 37 is larger than the outer diameter of the large diameter portion 18, and the support body 35 is installed so as to sandwich the pipe 37. The inner diameter of the support 35 is smaller than the outer diameter of the annular body 39 attached to the pipe 37. Further, the pipe 37 is supported so as to be slidable in a direction perpendicular to the axis.

Thus, a flow path is formed between the inner surface of the pipe 37 and the outer surface of the extension rod 3, and when the large diameter portion 18 of the extension rod 3 reaches the pipe 37, the flow path is narrowed. Further, the pipe 37 can be moved horizontally and eccentrically.

According to this third embodiment, the same effects as those of the second embodiment can be obtained, and at the same time, there is an advantage that the support body 35 can be manufactured easily.

FIG. 8 shows a fourth embodiment of the present invention, in which the same parts as those in FIG. 1 are indicated by the same reference numerals, and the explanation of the overlapping parts will be omitted. The difference between FIG. 2 and FIG. 1 is that a second flow regulator 40 having the same shape as the flow regulator 21 is provided above the flow regulator 21. The flow regulator 40 is suspended from the handling head 4 by a spring wire 41.

The extension rod 3 is formed with a disk-shaped large diameter portion 42 that is shorter in size than the large diameter portion 18 shown in FIG. However, the diameter is larger.

When the spring wire 41 is pulled up to the extent that it becomes slack, it is supported on the flow rate regulator 21 by its own weight, and at the same time, the large diameter portion 42 of the extension portion 3
The outflow path of the coolant is narrowed by the hole 43 of the second flow rate regulator 40.

[Effects of the Invention] As explained above, according to the present invention, a flow rate regulator that can be raised and lowered is provided separately from the control rod body, and the flow rate regulator controls the flow between the control rod body and the guide tube. The cross-sectional area of the passage is narrowed to reduce the gap flow of low-temperature coolant flowing through this gap, and when the large diameter part formed on the extension rod reaches the flow passage restriction during constant stroke lifting, the coolant flow rate is further increased. can be reduced. This allows the coolant outlet temperature to be kept high even in a state where the control rod calorific value is small, so the difference between the coolant outlet temperature and the fuel outlet temperature becomes small, and problems caused by thermal fluctuations can be prevented.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing a conventional control rod assembly;
FIG. 2 is a longitudinal sectional view showing a first embodiment of the control rod assembly according to the present invention, and FIG. 3 is a graph diagram for explaining the effects of the conventional control rod assembly and the control rod assembly according to the present invention. , FIG. 4 is a vertical cross-sectional view showing a second embodiment of the control rod assembly according to the present invention, FIG. 5 is a vertical cross-sectional view showing an enlarged section A of FIG. FIGS. 7 and 8 are partial sectional views showing only essential parts of the third and fourth embodiments of the control rod assembly according to the present invention. 1... Guide tube, 2... Control rod body, 3... Extension rod, 4... Handling head, 5... Protection tube,
6... Entrance nozzle, 7... Coolant inlet, 8... Coolant outlet, 9... Dash pot, 10... Dash ram, 11... Coolant inlet, 12... Control rod element, 13, 14 ... Stator, 15 ... Coolant outlet, 16 ... Gripping part, 1
7... Core support plate, 18... Large diameter portion, 19... Flow rate restrictor, 20... Channel hole, 21... Flow rate regulator,
22... Coolant channel, 23... Curved surface, 24... Small gap, 25... Coolant channel, 26... Channel throttle,
27... Circular pipe portion, 28... Spacing, 29... Small protrusion, 30... Large diameter hole, 31... Spacing member, 32...
... Channel hole, 33 ... Annular plate, 34 ... Upper guide tube, 35 ... Support body, 36 ... Protrusion, 37 ... Pipe, 38 ... Channel restrictor, 39 ... Annular body, 40
...Flow rate regulator, 41 ...Spring wire, 4
2... Large diameter portion, 43... Channel hole.

Claims (1)

[Scope of Claims] 1. A guide tube installed in the reactor core, through which coolant flows upward, and having a handling head at the top and an entrance nozzle at the bottom; a control rod body having a built-in neutron absorbing material connected to the lower end of the extension rod; a large diameter portion formed in the extension rod; a flow passage restrictor whose portion is pulled up to adjust the flow rate of the coolant; and a coolant removably placed on the upper end of the control rod body and formed between the body and the inner surface of the guide tube. A control rod assembly characterized by comprising a flow rate regulator that narrows the cross-sectional area of the flow path. 2. The control rod assembly according to claim 1, wherein at least one stage of annular body movable in the radial direction is inserted into the flow path restrictor. 3. The control rod assembly according to claim 1, wherein the flow rate regulator is an annular body that can fall under its own weight. 4. The control according to claim 1, wherein the flow path restrictor is supported by a fall prevention member that can fall at any position from the handling head provided on the guide tube to the flow rate regulator. stick assembly.