JP2000227491A - Control rod assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a control rod assembly capable of removing a thermal stress generated on the upper part of a reactor core, and capable of removing a delay of an insertion time at the time of a scrum. SOLUTION: The inner diameter of a guide pipe 1 and the outer diameter of a control rod body 2 are narrowed to such a degree that the pressure between an entrance nozzle 3 and the control rod body 2 becomes higher than those of the outlet part of a guide pipe handling head 4 and the inlet part of the entrance nozzle 3, at the time of rapid insertion when a scrumming operation of the control rod body 2 is executed by a control rod driving mechanism, and a flow rate of a liquid metal coolant flowing between the guide pipe 1 and the control rod body 2 is restricted, and flowing of the liquid metal coolant into the control rod body 2 is accelerated, to thereby enable to reduce the maximum temperature difference between the control rod body 2 and the outlets of a control rod assembly and a fuel assembly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod assembly for controlling the core power of a nuclear reactor by liquid metal cooling.

[0002]

2. Description of the Related Art Generally, a control rod assembly for controlling the core power of a nuclear reactor by liquid metal cooling is provided with a control rod main body containing a plurality of neutron absorbers in a guide tube so as to be movable up and down.
The core power is controlled by inserting and removing the neutron absorber into the core region.

The neutron absorber built in the control rod body is
Heat is generated by absorbing neutrons in the core. For this reason, inside the guide tube, a structure in which the liquid metal coolant can flow in and out of the control rod body is provided, and the liquid metal coolant flowing between the neutron absorbers heats the neutron absorber. So that it absorbs heat.

That is, in such a control rod assembly, since the neutron absorber inside the control rod body generates heat by being inserted into the core region, the liquid metal flowing through the control rod assembly is removed to remove the heat. It is necessary to distribute the coolant to the neutron absorber collection portion inside the control rod body as much as possible.

[0005] Thus, the temperature difference between the outlet temperature of the liquid metal coolant of the control rod assembly and the outlet temperature of the fuel rod assembly adjacent to the control rod assembly can be reduced, and the problem of thermal stress described below is alleviated. it can.

[0006]

However, since the pressure loss of the neutron absorber inside the control rod body is large, if the liquid metal coolant is concentrated on this part, it will be inserted during the scram operation of the control rod assembly. The reaction force becomes too large, causing problems such as a longer scrum time.

[0007] On the other hand, in view of the performance requirement of reducing the scrum time, it is desirable to suppress the reaction force when inserting the scrum. For that purpose, it is necessary to reduce the pressure loss around the control rod body, so the flow rate distribution of the liquid metal coolant must be made to concentrate on the neutron absorber inside the control rod body. Instead, it concentrates on the gap between the control rod body and the guide tube.

In this case, the outlet temperature of the liquid metal coolant of the control rod assembly is, for example, several hundred degrees centigrade compared to the outlet temperature of the liquid metal coolant of the fuel rod assembly adjacent to the control rod assembly. To a lesser extent, large temperature differences occur. Moreover,
Since the striking temperature wave by the liquid metal coolant from the control rod assembly and the fuel assembly having such a temperature difference hits the rectifier at the lower end of the core upper mechanism provided at the upper part of the core, The rectifier could generate large and repeated thermal stresses, resulting in local thermal fatigue.

Therefore, in order to remove the heat generated in the control rod body by the liquid metal coolant as much as possible and to reduce the difference in the outlet temperature between the control rod assembly and the fuel assembly, the control rod is required. Increase the flow rate of liquid metal coolant flowing inside the body,
The flow rate outside the control rod body that does not contribute to heat removal must be reduced.

In such a case, since the pressure loss at the outlet of the control rod assembly increases, the scram time of the control rod body is delayed as described above. As described above, in the conventional control rod assembly, there is a trade-off relationship between the scrum performance and the outlet temperature difference, and it is difficult to satisfy both conditions.

An object of the present invention is to provide a control rod assembly that can eliminate thermal stress generated in the upper part of the core and can prevent a delay in insertion time during scram.

[0012]

According to a first aspect of the present invention, there is provided a control rod assembly provided in a reactor core of a liquid metal-cooled reactor, having a guide tube handling head at an upper end and a liquid metal cooling head at a lower end. A guide tube having an entrance nozzle through which a material is introduced, and a control rod driving mechanism which is provided in the guide tube so as to be movable up and down, has a plurality of neutron absorbers built therein, and is inserted into a center hole of the guide tube handling head at an upper portion. In a control rod assembly including a control rod main body having a control rod handling rod connected to the control rod assembly, the gap between the guide tube inner diameter and the control dedicated main body outer diameter is controlled by a control rod driving mechanism. At the time of rapid insertion during scram operation, the gap between the entrance nozzle and the control rod body is within a range that allows a delay in scram operation.

In the control rod assembly according to the first aspect of the present invention, the pressure between the entrance nozzle and the control rod main body is controlled by the guide pipe handling during rapid insertion when the control rod main body is scrammed by the control rod driving mechanism. The inner diameter of the guide tube and the outer diameter of the control rod main body are reduced to such an extent that they are higher than the head outlet part and the entrance nozzle inlet part, and the flow rate of the liquid metal coolant flowing between the guide pipe and the control rod main body is restricted. It facilitates the flow of liquid metal coolant into the body and allows for a reduction in the maximum temperature difference between the control rod assembly and the outlet of an adjacent fuel assembly.

According to a second aspect of the present invention, there is provided a control rod assembly,
2. The entrance nozzle according to claim 1, wherein the control rod body has a tapered or rounded corner at a portion serving as an inlet of a liquid metal coolant flowing backward when the control rod drive mechanism performs rapid insertion accompanying a scram operation. It is characterized by.

In the control rod assembly according to the second aspect of the present invention, in addition to the operation of the first aspect, at the time of rapid increase when the control rod body is scrammed by the control rod driving mechanism,
Even if the rotation pressure of the entrance / separation and the control rod body is higher than the guide tube handling head outlet and the entrance nozzle entrance, the entrance nozzle passes through the entrance of the liquid metal coolant having a tapered or rounded corner. The pressure loss at the time of backflow to the side is reduced, the backflow can be easily performed, and the delay of the scrum time can be prevented. Also, at normal times, it is possible to maintain an appropriate pressure loss in the forward flow for maintaining the flow rate according to the core flow distribution.

A control rod assembly according to a third aspect of the present invention is
In the entrance nozzle according to the first or second aspect of the present invention, a change in a cross-section of a portion serving as an outlet of a liquid metal coolant that flows backward when the control rod main body performs a rapid insertion accompanying a scram operation by a control rod driving mechanism. It is characterized by being moderate.

In the control rod assembly according to the third aspect of the present invention, in addition to the operation of the first or second aspect, the entrance of the control rod body at the time of rapid insertion when the control rod driving mechanism is scrammed is performed. Even when the pressure between the nozzle and the control rod body is higher than the guide tube handling head outlet and the entrance nozzle inlet, the cross section changes through the gently formed liquid metal coolant outlet,
Backflow can be more easily made to the entrance side, and the prevention of delay of the scrum time can be further enhanced.

A control rod assembly according to a fourth aspect of the present invention
The entrance nozzle according to claim 1, wherein the control rod main body is provided with a backflow coolant channel for passing a liquid metal coolant flowing backward when the control rod drive mechanism performs rapid insertion accompanying scram operation, A valve is provided in the coolant flow passage at the time of backflow, and the valve is opened at the time of backflow and normally closed.

In the control rod assembly according to the fourth aspect of the present invention, in addition to the function of the first aspect of the invention, the entrance nozzle and the control nozzle can be controlled during rapid insertion when the control rod body is scrammed by the control rod driving mechanism. When the pressure between the rod body and the outlet of the guide tube handling head and the entrance of the entrance nozzle becomes higher, the backflow can easily flow through the coolant flow path at the time of backflow to the entrance side, and the delay of the scrum time is prevented. Can be. Also, at normal times, it is possible to maintain an appropriate pressure loss with respect to the forward flow for maintaining the flow rate according to the core flow rate distribution.

According to a fifth aspect of the present invention, there is provided a control rod assembly comprising:
In the entrance nozzle according to the first aspect of the present invention, when the control rod main body forms an outlet of the liquid metal coolant that flows backward when the control rod drive mechanism performs rapid insertion in accordance with the scram operation, the liquid metal coolant is normally used. A spiral fluid diode having a smaller fluid resistance at the time of reverse flow than that at the time of forward flow is provided.

According to a fifth aspect of the present invention, there is provided a control rod assembly comprising:
In addition to the effect of the invention of claim 1, during the rapid insertion when the control rod main body is scrammed by the control rod driving mechanism, the pressure between the entrance nozzle and the control rod main body increases the guide tube handling head outlet and the entrance. When the height is higher than the nozzle inlet, the backflow can be easily made through the spiral fluidic diode in which the fluid resistance becomes small at the time of backflow to the entrance side, and the delay of the scrum time can be prevented. In addition, it is possible to maintain an appropriate pressure loss with respect to a forward flow for maintaining a flow rate in accordance with the core flow rate distribution through a spiral fluid diode having a large fluid resistance in normal times.

The control rod assembly according to the invention of claim 6 is:
In the control rod body according to the present invention, when the control rod body performs a rapid insertion accompanying a scram operation by a control rod driving mechanism, a corner of a portion on the inlet side of a liquid metal coolant flowing in a normal forward direction. Is tapered or rounded.

In the control rod assembly according to the sixth aspect of the present invention, in addition to the operation of the first aspect, at the time of rapid insertion when the control rod body is scrammed by the control rod driving mechanism,
Even when the pressure between the entrance nozzle and the control rod body is higher than the guide tube handling head outlet and the entrance nozzle inlet, the guide tube handling head exit side passes through the tapered or rounded inlet hole. Out of the liquid metal coolant can be easily performed, and delay of the scrum time can be prevented.

A control rod assembly according to a seventh aspect of the present invention
In the control rod body according to claim 1 or 6,
When the control rod main body performs rapid insertion accompanying a scrum operation by a control dedicated drive mechanism, a change in a cross section of a portion on an outlet side of a normal forward flowing liquid metal coolant is moderated. .

In the control rod assembly according to the seventh aspect of the present invention, in addition to the functions of the first or sixth aspect, the entrance of the control rod body at the time of rapid insertion when the control rod main body is scram-operated by the control rod driving mechanism. Even when the pressure between the nozzle and the control rod body is higher than the guide tube handling head outlet and the entrance nozzle inlet, the cross section changes through the gently formed outflow hole to the guide tube handling head outlet. Out of the liquid metal coolant can be easily performed, and delay of the scrum time can be prevented.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a control rod assembly according to the first embodiment of the present invention. In the first embodiment, the gap between the inner diameter of the guide tube 1 and the outer diameter of the control body 2 (the width of the coolant passage 21) is a predetermined gap, and the gap is the control rod. At the time of rapid insertion when the main body 2 is scrammed by the control rod drive mechanism, the gap between the entrance nozzle 3 and the control rod main body 2 is set within a range in which the delay of the scrum operation is allowed.

That is, when the control rod body 2 is rapidly inserted, the pressure between the entrance nozzle 3 and the control rod body 2 becomes higher than the outlet of the guide tube handling head 4 and the inlet of the entrance nozzle 4. The inner diameter of the guide tube 1 and the outer diameter of the control rod main body 2 are reduced, and the flow rate of the liquid metal coolant flowing between the guide pipe 1 and the control rod main body 2 is limited. This facilitates inflow and allows for a reduction in the maximum temperature difference between the control rod assembly and the outlet of an adjacent fuel assembly.

FIG. 1 shows a state in which the control rod body 2 housed in the guide tube 1 is fully inserted. The control rod main body 2 is housed inside the guide tube 1 so as to be movable up and down. The guide tube 1 has an entrance nozzle 3 at its lower end and a guide tube handling head 4 at its upper end. ing.

The entrance nozzle 3 is mounted on a core support plate 5 fixed to the nuclear reactor. Desorption from the reactor is performed by supporting the guide tube handling head 4 by a mechanism not shown. At the lower end of the entrance nozzle 3,
A coolant inlet hole 6 for introducing a liquid metal coolant such as liquid sodium is formed in the guide tube 1.

A coolant discharge hole 7 for discharging the liquid metal coolant introduced into the guide tube 1 is provided at the upper end of the guide tube 1. At a position slightly below the coolant discharge hole 7 inside the guide tube 1, a fixing plate 8 is integrally provided so as to vertically divide the inside of the guide tube 1 into two parts. In the center of the fixing plate 8, a center hole 9 for flowing the liquid metal coolant is provided.

The control rod body 2 includes a plurality of neutron absorbers 1
1, an upper lattice plate 13 supporting the upper ends of the neutron absorbers 11, a lower lattice plate 14 supporting the lower ends of the neutron absorbers 11, a protective tube 15 for accommodating them, and an upper end of the protective tube 15. And a control rod handling rod 16 for pulling out the control rod body provided in the control rod.
The upper grid plate 13 and the lower grid plate 14 are provided with a plurality of coolant circulation holes 12 for passing the liquid metal coolant. Further, a ram portion 18 having a plurality of coolant inflow holes 17 is provided at a lower end portion of the protection tube 15,
A plurality of coolant discharge holes 19 are provided at the upper end of the protection tube 15.

The outer diameter of the protection tube 15 is set smaller than the inner diameter of the guide tube 1 so that a coolant flow path 21 is formed in a gap between the two, and each neutron absorption is performed. A coolant channel 22 is also formed in the gap between the bodies 11. The control rod handling rod 16 is connected to a control rod drive mechanism (not shown) through the center hole 9 and the coolant discharge hole 7 of the guide pipe handling head 4. Pulled up at the top.

Here, in the first embodiment, the inner diameter of the guide tube 1 and the outer diameter of the control body 2 (the outer shape of the protection tube 15).
, That is, the width of the coolant flow path 21,
At the time of rapid insertion, the entrance nozzle 3 and the control rod body 2
The gap between the pressure and the pressure is as narrow as possible within a range in which the delay of the scrum operation is allowed. As a result, at normal times,
The flow rate of the liquid metal coolant flowing between the guide tube 1 and the control rod main body 2 is limited, and the flow of the liquid metal coolant into the control rod main body 2 is promoted. Therefore, the heat generated by the neutron absorber 11 is absorbed by the liquid metal coolant. On the other hand, when the control rod main body 2 is rapidly inserted, the operation can be performed within a range in which the delay of the scrum operation is allowed. Therefore, the temperature difference between the control rod assembly and the outlet of the adjacent fuel assembly can be reduced.

Next, the operation of the control rod assembly according to the first embodiment thus configured will be described. Now, when the control rod body 2 is at the full insertion position shown in FIG. 1, the liquid metal coolant introduced into the guide tube 1 from the coolant inlet 6 of the entrance nozzle 3 is indicated by an arrow in FIG. As described above, the coolant flows into the center hole 9 of the fixing plate 8 via the coolant passage 21 or the coolant passage 22. Then, the coolant passes through the center hole 9 of the fixed plate 8 and is discharged from the coolant discharge hole 7.

Since the gap of the coolant channel 21 is sufficiently small,
Although the total flow rate of the liquid metal coolant is reduced by the increased pressure loss, the flow rate distribution of the liquid metal coolant flowing inside the control rod body 2 is increased, and the ratio of the liquid metal coolant that contributes to heat removal is increased. Therefore, since the outlet temperature of the control rod assembly increases, the temperature difference between the outlet temperature of the fuel rod assembly adjacent to the control rod assembly and the temperature of the fuel rod assembly are alleviated. Can be prevented.

FIG. 2 shows a state in which the control rod body 2 has shifted from the withdrawn state to the scrum. As shown in FIG. 2, when the control rod main body 2 is rapidly inserted by the scram operation, a backflow 23 of the liquid metal coolant occurs due to the internal pressure generated by the operation of the control rod main body 2.

That is, there is a turbulence in the flow at the time of outflow as shown by an arrow in FIG. 2 and the pressure loss at the time of backflow is large, and the pressure between the entrance nozzle 3 and the control rod main body 2 increases the guide pipe handling. It is higher than the outlet of the head 4 and the inlet of the entrance nozzle 3. In the first embodiment, the delay of the scrum time due to the internal pressure generated by the backflow is set within an allowable range. Therefore, the liquid metal coolant can flow as much as possible in the control rod body 2 in the normal state, and the scram time can be delayed in the scram.

Next, a second embodiment of the present invention will be described. FIG. 3 is a longitudinal sectional view of a portion of an entrance nozzle 2 of a fuel assembly according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in that the corner of the portion serving as the inlet of the backflow 23 of the liquid metal coolant generated when the control rod body 2 is rapidly inserted is tapered or rounded. In addition, the change in the cross section of the portion serving as the outlet of the liquid metal coolant is moderated.

In FIG. 3, the backflow 23 of the liquid metal coolant
The corner of the portion S1 serving as the entrance of the taper is tapered or rounded. And the change of the cross section of the part T1 which becomes the outlet of the liquid metal coolant is moderated. Similarly, even in the middle of the flow of the liquid metal coolant, the corner of the portion S2 serving as the inlet of the backflow 23 is tapered or rounded, and the change in the cross section of the portion T2 serving as the outlet of the liquid metal coolant is moderated. .

As described above, the shape of the coolant inlet hole 6 of the entrance nozzle 3 is reduced by tapering or rounding the corners of the portions S1 and S2 serving as the inlets of the backflowing liquid metal coolant so that the pressure loss during backflow is reduced. By gradually changing the cross section of the portions T1 and T2 serving as outlets of the liquid metal coolant flowing backward, the pressure loss at the time of the backflow to the entrance nozzle 3 side is reduced, and the backflow can be easily carried out. Therefore, it is possible to prevent a delay in the scrum time and to maintain an appropriate pressure loss in the forward flow for maintaining a flow rate according to the core flow rate distribution in normal times.

Next, a third embodiment of the present invention will be described. FIG. 4 is a longitudinal sectional view of a portion of an entrance nozzle 2 of a fuel assembly according to a third embodiment of the present invention. The third embodiment is different from the first embodiment in that, in addition to the normal coolant passage 27, the coolant flow at the time of reverse flow for passing the liquid metal coolant flowing backward at the time of rapid insertion of the control rod body 2 is described. A passage 28 is provided, and a valve 25 that is opened in the backflow and closed in the normal state is provided in the backflow coolant passage 28.

FIG. 4 shows a state in which the control rod body 2 housed in the guide tube 1 is fully inserted. In the entrance nozzle 3, in addition to the normal coolant channel 27, a backflow coolant channel 28 is provided. A valve 25 that opens when the liquid metal coolant flows backward is provided in the backflow coolant passage 28, and the valve 25 is supported by an elastic body 26 for restoration. The arrows in FIG. 4 indicate the flow of the liquid metal coolant during normal times. In this normal state, the valve 25 is closed by the pressing force of the elastic body 26, so that the liquid metal coolant flows through the coolant channel 27 during normal times, the inside of the control rod body 2 and the coolant channel 21. Go.

FIG. 5 shows a state in which the control rod body 2 in the control rod assembly according to the third embodiment of the present invention is shifted from the pulled-out state to the scrum. As shown in FIG. 5, when the control rod body 2 is rapidly inserted by the scram operation, the valve 25 is opened against the force of the elastic body 26 due to the internal pressure due to the backflow 23 of the liquid metal coolant.

As described above, normally, an appropriate pressure loss with respect to the forward flow for maintaining the flow rate according to the core flow rate distribution can be maintained, while the valve 25 is opened at the time of rapid insertion during scram operation. , It is possible to easily flow backward to the entrance nozzle 3 side, and it is possible to prevent a delay in the scrum time. That is, during the scram operation, the pressure between the entrance nozzle 3 and the control rod body 2 becomes higher than the outlet of the guide tube handling head 4 and the inlet of the entrance nozzle 3, and the valve 25 is opened.

Next, a fourth embodiment of the present invention will be described. FIG. 6 is a longitudinal sectional view of a portion of an entrance nozzle 2 of a fuel assembly according to a fourth embodiment of the present invention. The fourth embodiment is different from the first embodiment in that a spiral-type fluid diode 30 is provided at a portion serving as an outlet of a liquid metal coolant flowing backward when the control rod body 2 performs a scram operation. The spiral-type fluid diode 30 has such a characteristic that the fluid resistance becomes smaller when the liquid metal coolant flows backward as compared with the case where the liquid metal coolant flows in the normal forward direction.

FIG. 6A shows a state in which the control rod body 2 housed in the guide tube 1 is fully inserted, and FIG.
FIG. 3A is a cross-sectional view taken along line AA.

In the entrance nozzle 3 of FIG. 6 (a), a spiral fluid diode for controlling the flow of the liquid metal coolant is provided at the portion serving as the outlet of the liquid metal coolant flowing backward when the control rod body 2 performs the scram operation. 30 are provided. The spiral type fluid diode 30 includes a vortex chamber 31, a normal coolant outlet 32, and a normal coolant supply port 33. The normal flow of the liquid metal coolant in the normal direction causes the liquid metal coolant to flow. Is guided from the normal coolant supply port 33 to the vortex chamber 31, and a vortex is generated in the vortex chamber 31 to be discharged from the normal coolant discharge port 32. Therefore, as shown in FIG. 6B, a vortex is generated in the vortex chamber 31, so that the fluid resistance increases.

FIG. 7 shows a state in which the control rod body 2 in the control rod assembly according to the fourth embodiment of the present invention is shifted from the pulled-out state to the scrum. 7A is a longitudinal sectional view, and FIG. 7B is a sectional view taken along line BB of FIG. 7B.

As shown in FIG. 7 (a), when the control rod body 2 is rapidly inserted by the scram operation, the liquid metal coolant which has flowed in reverse from the coolant outlet 32 in the normal state in the spiral type fluid diode 30. Flows in the vortex chamber 31 without vortex 35
As a result, the coolant flows backward from the coolant supply port 33 during normal times.
Therefore, as shown in FIG. 7 (b), no vortex is generated in the vortex chamber 31, so that the fluid resistance is reduced.

As described above, in the normal state, the liquid metal coolant flowing from the normal-time coolant supply port 33 of the spiral-type fluid diode 30 generates a swirl flow 34 in the swirl chamber 31.
It normally exits through the coolant outlet 32. On the other hand, at the time of backflow, the liquid metal coolant which has flowed back from the normal coolant outlet 32 of the spiral type fluid diode 30 becomes a non-vortex flow 35 in the swirl chamber 31 and flows backward from the normal coolant supply port 33. I will do it.

From this, the fluid resistance is normally increased, and an appropriate pressure loss for the forward flow for maintaining the flow rate in accordance with the core flow rate distribution can be maintained. On the other hand, at the time of reverse flow, a vortex-free flow 35 is formed, so that the fluid resistance is small,
Accordingly, even when the pressure between the entrance nozzle 3 and the control rod body 2 becomes higher than the outlet of the guide tube handling head 4 and the entrance of the entrance nozzle 3 during the rapid insertion during the scram operation, the entrance nozzle 3 The backflow can be easily made to the side, and the delay of the scrum time can be prevented.

Next, a fifth embodiment of the present invention will be described. FIG. 8 is a longitudinal sectional view of a portion of an entrance nozzle 2 of a fuel assembly according to a fifth embodiment of the present invention. The fifth embodiment is different from the first embodiment in that when the control rod body 2 performs rapid insertion accompanying the scrum operation by the control rod drive mechanism, the liquid metal coolant flowing in the normal forward direction is used. The corner of the entrance side is tapered or rounded,
The change in the cross section of the portion on the outlet side of the normal liquid metal coolant flowing in the forward direction is moderated.

FIG. 8 shows a portion of the control rod body 2 on the inlet side of the liquid metal coolant flowing in the normal forward direction, the outer periphery of the lower end of the control rod body 2, and the coolant inlet hole 17 of the control dedicated body 2.
, The inlet of the coolant discharge hole 19, the upper lattice plate 13
And an inlet of the coolant passage hole 12 of the lower lattice plate 14, an inlet of the coolant discharge hole 7 of the guide tube handling head 4,
The corner of the entrance of the center hole 9 is tapered or rounded.

Further, a portion on the outlet side of the liquid metal coolant flowing in the normal forward direction, the outer periphery of the upper end of the control rod body 2, the coolant inlet 17, the coolant outlet 19 of the control body 2, and the upper grid plate 13 and the coolant flow holes 12 in the lower grid plate 14,
The change in the cross section at the outlet side of the coolant discharge hole 7 and the center hole 9 of the guide tube handling head 4 is moderated.

Therefore, at the time of rapid insertion during scram operation, the pressure between the entrance nozzle 3 and the control rod main body 2 becomes higher than the outlet of the guide tube hand ring head 4 and the inlet of the entrance nozzle 3. Even in this case, the liquid metal coolant can easily flow out to the outlet side of the guide tube handling head 4, and the delay of the scrum time can be prevented.

[0056]

As described above, according to the present invention,
Normally, the liquid metal coolant can be supplied to the control rod assembly of the control rod assembly, so that the outlet temperature of the liquid metal coolant discharged from the control rod assembly can be increased. Therefore, the temperature difference between the outlet temperature of the control rod assembly and the outlet temperature of the adjacent fuel rod assembly can be reduced, and the thermal stress and thermal fatigue of the reactor structure can be reduced.

Also, during the scram operation of the control rod body,
Since the liquid metal coolant flowing backward can be easily discharged, a delay in the insertion time during scram can be prevented, and the reliability of the nuclear reactor can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a control rod assembly according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a state in which the control rod body is shifted from a pulled-out state to a scrum according to the first embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a portion of an entrance nozzle of a fuel assembly according to a second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a portion of an entrance nozzle of a fuel assembly according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a state in which a control rod body is shifted from a pulled-out state to a scrum according to a third embodiment of the present invention.

FIG. 6 is an explanatory view of a part of an entrance nozzle of a fuel assembly according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a state in which the control rod body is shifted from a withdrawn state to a scrum according to a fourth embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of a part of an entrance nozzle of a fuel assembly according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Guide tube 2 Control rod main body 3 Entrance nozzle 4 Guide tube handling head 5 Core support plate 6, 17 Coolant inflow hole 7, 19 Coolant discharge hole 8 Fixing plate 9 Center hole 11 Neutron absorber 12 Coolant circulation hole 13 Upper part Lattice plate 14 Lower lattice plate 15 Protective tube 16 Control rod handling rod 18 Ram part 21, 22 Coolant flow path 23 Backflow 25 Valve 26 Elastic body 27 Normal coolant flow path 28 Reverse flow coolant flow path 30 Spiral type fluid diode 31 Vortex chamber 32 Normal coolant outlet 33 Normal coolant supply port 34 Spiral flow 35 Vortex-free flow

Claims (7)

[Claims] 1. A guide tube provided in a core of a liquid metal cooled reactor having a guide tube handling head at an upper end and an entrance nozzle at a lower end for flowing a liquid metal coolant, and a guide tube rising and falling into the guide tube. A control rod body having a plurality of neutron absorbers provided freely therein and having a control rod handling rod connected to a control rod driving mechanism through a center hole of the guide tube handling head at an upper portion thereof. In the control rod assembly, the gap between the inner diameter of the guide tube and the outer diameter of the control dedicated body is such that when the control rod body is rapidly inserted when the control rod drive mechanism performs scram operation, the entrance nozzle and the control rod A control rod assembly, characterized in that the pressure between the control rod and the main body is a gap within a range that allows a delay of the scrum operation. 2. In the entrance nozzle, a corner of a portion serving as an inlet of a liquid metal coolant flowing backward when the control rod main body performs rapid insertion accompanying a scram operation by a control rod driving mechanism is tapered or rounded. The control rod assembly according to claim 1, wherein: 3. In the entrance nozzle, a change in the cross-section of a portion serving as an outlet of a liquid metal coolant flowing backward when the control rod main body performs rapid insertion accompanying a scram operation by a control rod driving mechanism is moderated. The control rod assembly according to claim 1 or 2, wherein: 4. In the entrance nozzle, a backflow coolant channel is provided for passing a backflow liquid metal coolant when the control rod main body performs a rapid insertion accompanying a scram operation by a control rod drive mechanism. 2. The control rod assembly according to claim 1, wherein a valve that opens at the time of backflow and closes at normal time is provided in the coolant flow path at the time of backflow. 5. In the entrance nozzle, a liquid metal coolant is supplied to a portion serving as an outlet of a liquid metal coolant flowing backward when the control rod main body performs rapid insertion accompanying a scram operation by a control rod driving mechanism. 2. The control rod assembly according to claim 1, wherein a spiral-type fluid diode having a smaller fluid resistance at the time of backflow than at the time of backward flow is provided. 6. A corner of the control rod main body, which is located on the inlet side of a liquid metal coolant flowing in a normal forward direction when the control rod main body performs rapid insertion accompanying a scram operation by a control rod driving mechanism. The control rod assembly according to claim 1, wherein the control rod assembly is formed in a tapered or round shape. 7. A cross section of a part of the control rod main body, which is located at an outlet side of a liquid metal coolant flowing in a normal forward direction, when the control rod main body performs a rapid insertion accompanying a scram operation by a control dedicated driving mechanism. The control rod assembly according to claim 1 or 6, wherein the change of the control rod is gradual.