JPS6364756B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neutron shield installed around the core of a fast breeder nuclear reactor.

The neutron shielding body installed around the fast breeder reactor core (hereinafter referred to as the reactor core) has the purpose of effectively utilizing neutrons generated in the reactor core and preventing neutrons from leaking outside the reactor. have

For this reason, it is necessary for the neutron shield to contain a shield at a predetermined position during its lifetime, even if it is not necessary to achieve the above-mentioned purpose.

On the other hand, since the neutron shield is installed just outside the reactor core, it will be exposed to high temperatures and high neutron irradiation.

Under this environment, the neutron shield undergoes deformation due to temperature distribution in its own circumferential direction, swelling of the material due to irradiation, and deformation of other core components from the outside. Loads, as well as loads due to collisions between neutron beams and shields due to earthquakes, and fluid force, act on the spacer pads that mutually restrain movement in the lateral direction.

Conventionally, neutron shielding bodies have been constructed with an integrated hexagonal rod, or several thin rod-shaped shields are bundled with upper and lower restraint plates, and these restraint plates are fixed to a lapper tube or entrance nozzle for support. A structure in which a large number of flexible bodies are stacked on a disc, a rod for supporting these flexible bodies is passed through the center of the flexible bodies, and the lower part of this rod is fixed to the entrance nozzle. There was a method of supporting the upper part using a spring and screw structure.

However, in this case, if the neutron shield is deformed due to the reasons mentioned above, it is extremely difficult to alleviate the stress applied to the entrance nozzle during deformation because the shield itself has a rigid structure. It is the main factor that determines the lifespan of the body. In order to ensure the integrity of this part, it is necessary to reduce stress.

However, there are problems such as the filling rate of the internal sheathing bodies does not increase, and the structure that supports a large number of sheathing bodies is complex and requires a lot of effort to manufacture. This has the disadvantage that the shape of the reactor is not uniform inside the reactor, making it difficult to grasp the pressure drop inside the reactor, which also interferes with the flow distribution plan for the entire reactor core.

Furthermore, in each structure except for the integrated type, since the wrapper tube has a flow path 5 for flowing the coolant necessary for heat removal and thermal stress reduction, a cylindrical or rod-shaped internal shield body 6 is installed at one end. is attached to the entrance nozzle and is built in at a certain distance from the wrapper tube 1.

Therefore, a very large stress is generated in the spacer pad, and depending on the applied force, there is a risk of damage, deformation, crushing, etc.

If this happens, not only will it be difficult to convert the neutron shield itself, but the normal position of the core matrix will shift due to the loss of mutual restraint of lateral movement, and the handling of other core components will be difficult. This poses a huge problem in terms of reactor safety, as it not only interferes with control rod replacement but also with the ease of inserting control rods.

The present invention has been made in view of the above points, and its first object is to provide a structure that prevents damage and deformation of the wrapper tube and handling head due to external loads.

The second purpose is to maintain the flexibility of the neutron shield as a whole even if the entire neutron shield deforms in the axial direction due to the reasons mentioned above, and to alleviate the stress generated at the entrance nozzle. The goal is to obtain a structure that is possible.

A third objective is to obtain a structure that allows easy calculation of internal pressure loss, facilitates flow distribution planning for the entire reactor core, and facilitates manufacturing.

The fourth objective is to obtain a structure that increases the damping effect.

The present invention will be described below with reference to the drawings of one embodiment.

In FIGS. 1 and 2, the entrance nozzle 1 is inserted into a connecting pipe installed on the core support plate, and allows the neutron shield to stand on its own.
It has a coolant passage 2 inside. The wrapper tube 3 is connected to the entrance nozzle 1 and forms a flow path 4 that communicates with the coolant path 2, and at the same time, the tube 3 is connected to the entrance nozzle 1 and forms a flow path 4 that communicates with the coolant path 2. It is received by spacer pads 5 which are mutually constrained and transmitted to other core components.

A handling head 6 having a hexagonal shape with an upper pad is attached to the upper part of the wrapper tube 3, has a structure that can be handled by a refueling machine, and has a coolant outlet 7.

The internal shield body 8 is placed in the wrapper tube 3 above the entrance nozzle 1, extends into the handling head 6 in the axial direction as far as there is no problem when handling it with a fuel exchanger, and is divided into several pieces. Only the parts of the wrapper tube 3 and handling head 6 that are assembled in a fitting structure and have a spacer pad 5 have a structure in which the play between them is minimized or they are in contact with the inside of the wrapper tube 3 and handling head 6, so that the coolant can be kept inside and outside. It has a flow path 4. Figure 3 shows its detailed diagram.

The structure of the internal shrinkage body is shown in Figures 4 and 5.
As shown in the figure, it is also possible to use an internal shield body 8a that contacts the entire area inside the wrapper tube 3 corresponding to the spacer pad 5, or an internal shield body 8c that makes surface contact with the spacer pad 5 partially.

Next, the effects will be explained.

Neutrons from the core are reflected or absorbed by the internal shielding body 8 and are effectively used for fuel combustion, and by installing a large number of these neutron shielding bodies outside the core, neutrons are prevented from flowing outside the reactor. Prevents leakage.

The internal shield body 8 is inscribed with the inner portions of the wrapper tube 3 and the handling head 6 having the spacer pad 5 with little play or no play, so that the above-mentioned external load acts on the spacer pad 5. , a wrapper tube 3 having a spacer pad 5 and a handling head 6
Even if it tries to deform, the load from the outside is suppressed by the internal shrinkage body 8 installed inside each of the wrapper tube 3 and handling head 6, so that no breakage or deformation will occur.

In addition, the material of the wrapper tube 3 is, for example, 20% cold-worked stainless steel, while the stiff tube 8
uses annealed stainless steel material. Swelling is greater in annealed material than in 20% cold-worked material. Therefore, the expansion of the flexible body 8 increases, and an outward force acts on the wrapper tube 3. If the internal shrinkage body 8 is inscribed in the laparium tube 3 over the entire axial direction,
Since an outward pushing force acts on the entire surface of the wrapper tube 3, the stress is expected to be quite large. However, according to the structure of the present invention, the wrapper tube 3 and the inner sheathing body 8 installed therein are only the portions that have the spacer pad 5, so the force that forces the wrapper tube 3 outward is also dispersed in the axial direction. and stress is reduced.

In addition, the internal flexible body 8 is divided into several parts, and the only part that is inscribed in the wrapper tube 3 is the part that has the spacer pad 5, so even if the wrapper tube 3 is deformed by an external load, it will not be damaged. The bodies themselves can bend freely and do not affect each other.

Further, heat generated by neutron irradiation of the internal shield and heat transferred from the outside are cooled by a coolant flowing in from a passage 2 formed in the entrance nozzle 1. For this reason, the Ratsupa canal 3 and the internal sinusoid body 8
A coolant passage 4 is formed between the inner shield body 8 and a coolant passage 4 therein.
The internal shield body 8 is held down by the lower end of the handling head 6 provided at the upper part of the wrapper tube 3 to prevent it from flowing out due to the flow of the coolant.

Furthermore, when the inner shield body 8 is assembled into the wrapper tube 3, since it is inscribed only in the portion having the spacer pad 5, it can be easily assembled even if the respective dimensional tolerances are taken into account.

On the other hand, the internal shielding body 8 in the axial direction has a length that extends into the inside of the handling head 6 to a point where it does not pose a problem when handling with a fuel exchanger, so that it This results in a structure with a larger yaw body effect.

As explained above, according to the neutron shielding body of the present invention, the spacer pad is inscribed inside the wrapper tube and the handling head with less play or no play, thereby preventing the wrapper tube from being affected by external loads. Also, the handling head can be prevented from being damaged or deformed, and the spacer pads can mutually restrict lateral movement, keeping the core matrix in its normal position and maintaining the safety of the reactor.

In addition, the force that pushes the wrapper tube outward due to the swelling of the internal flexible body can be dispersed in the axial direction, so the stress on the wrapper tube is reduced and its life can be extended.

Furthermore, a structure can be obtained that allows easy assembly of the internal shield body into the wrapper tube during manufacturing.

Furthermore, the Ratsupa tube has a relatively flexible structure,
By using an internal shield that is divided into several parts and inscribed only in the part that has the spacer pad, the stress applied to the entrance nozzle can be minimized even when the neutron shield is deformed, thereby extending the lifespan. It can be made longer.

In addition, by using a fitting method to connect the shield body with the entrance nozzle and between the shield bodies, it is possible to secure the coolant flow path shape with a very simple structure. In addition to the simple shape of the shield, it is also easy to plan the flow distribution throughout the core.

In addition, by extending the internal shield body into the interior of the handling head to a point where it does not pose a problem when handling it with a fuel exchanger, the shielding effect can be increased.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a neutron shield according to the present invention, FIG. 2 is a cross-sectional view taken along the spacer pad portion of FIG. 1, and FIG. 3 is a cross-sectional view taken along the line AA in FIG. 4 and 5 are cross-sectional views showing other embodiments of the spacer pad portion shown in FIG. 2. 1...Entrance nozzle, 3...Ratsupa tube,
4...Flow path, 5...Spacer pad, 6...Handling head, 7...Internal flexible body.

Claims (1)

[Claims] 1 A polygonal wrapper tube, an entrance nozzle connected to the lower end of the wrapper tube, a handling head formed at the upper end of the wrapper tube, and an internal section installed with a coolant flow path formed inside the wrapper tube. A neutron shielding body comprising a shield body and a spacer pad provided on a side wall of the wrapper tube, characterized in that an internal shield body corresponding to the spacer pad portion is installed in contact with the wrapper tube. A neutron-emitting body.