JPS5834390A - Liquid metal cooled type fast breeder - 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 The present invention promotes mixing in the upper plenum of the reactor vessel in a loop fast breeder reactor using liquid IJ as a coolant, and prevents thermal shock and thermal deformation of the reactor vessel and outlet nozzle. Relating to a liquid metal cooled fast breeder reactor protected from

More specifically, the present invention deals with a situation in which during a reactor scram, the core outlet coolant temperature drops rapidly, the flow rate becomes low as the pump coasts down, and the Na temperature in the upper plenum is high at the top and low at the bottom. As a result, thermal stress becomes extremely severe at the outlet nozzle due to the temperature difference between the coolant flowing into the inner cylinder from the annulus section between the furnace vessels and the coolant flowing from the flow hole. It is an object of the present invention to provide a nuclear reactor characterized in that it is provided with an inner cylinder having the following characteristics.

Conventionally, an upper core mechanism necessary for in-core instrumentation is installed in the upper plenum inside the reactor vessel of a loop-type nuclear reactor, and an inner cylinder is installed inside the reactor vessel. The inner cylinder has the function of promoting mixing of the coolant in the upper plenum and mitigating thermal shock and thermal deformation of the reactor vessel and outlet piping (outlet nozzle) that may occur during transient operations. This consists of a flow path in which the flow of coolant in the upper plenum passes through a plurality of inner cylinder flow holes located at the height of the reactor vessel outlet piping, which are directly guided from the upper part of the core to the reactor vessel outlet piping, and a core assembly. After rising radially from the body outlet through the lower part of the upper core mechanism or rising along the inner surface of the inner cylinder, the flow rate flows between the top of the inner cylinder and the cover gas liquid level toward the inner wall of the reactor vessel, and then inside. The annulus section between the cylinder and the furnace vessel is divided into two routes: a flow path that descends and leads to the outlet piping of the furnace vessel. This has the effect of alleviating thermal shock and thermal deformation of the reactor vessel wall and reactor vessel outlet piping when the coolant temperature at the outlet of the core fuel assembly changes suddenly, such as immediately after a reactor scram. .

The flow rate in the upper plenum is such that the coolant that has flowed out of the core assembly flows radially through the lower part of the upper core mechanism and upward along the inner cylinder. Most of the coolant flows from the upper end of the inner cylinder to the outlet nozzle through the annulus between the inner cylinder and the inner wall of the reactor vessel. Further, a portion of the coolant passes through a flow hole provided in the abdomen of the inner cylinder facing the outlet nozzle, mixes with the coolant from the upper annulus, and flows out from the outlet nozzle.

This coolant passes through a heat exchanger, a circulation pump, etc., and then returns to the inlet nozzle of the furnace vessel.

In a nuclear reactor having the above structure, the coolant flow rate gradually decreases when there is a scram, and the flow rate becomes about 10% of the rated operation. The temperature of the coolant from the core assembly may change suddenly after a scram. As mentioned above, coolant with a low (or high) temperature flows out directly from the inner cylinder flow hole, and rises along the inner surface of the inner cylinder and descends along the annulus between the inner cylinder and the furnace vessel. There are two routes for the coolant to reach the outlet nozzle, and there is a time gap between these two routes until the coolant reaches the outlet nozzle.

At this time, rapid temperature changes and temperature fluctuations occur in the vicinity of the outlet nozzle, as well as areas with large temperature differences, which has the drawback of causing thermal shock and thermal deformation of the structural material.

The present invention has been made in order to eliminate the above-mentioned drawbacks.The present invention has been made to reduce the diameter of the conventionally provided inner cylinder flow hole and to form a plurality of inner cylinder flow holes in multiple stages above the furnace vessel outlet nozzle position. By installing these separately, it is possible to prevent the coolant flowing out from the core fuel assembly from directly flowing out from the flow hole to the outlet nozzle, increase the proportion of the flow rate from the upper 70-hole, and increase the flow rate within the annulus. It is an object of the present invention to provide a liquid metal cooled fast breeder reactor that can moderate rapid temperature changes near an outlet nozzle and prevent thermal shock and thermal deformation of structural materials by improving mixing.

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

That is, the fast breeder reactor according to the present invention, as shown in FIG. A supporting plate 5 is provided horizontally, and an inlet plenum 6 is provided in the furnace vessel 3 located below the supporting plate 5.

Further, a blanket fuel assembly 7 and a reactor core 8ai for loading the fuel assemblies are installed above the support plate 5, and an outlet plenum 9 for cooling material is provided in the reactor vessel 3 located near the outlet 2. There is.

Furthermore, a shielding plug 11 filled with cover gas 10 is provided in an airtight manner in the outlet plenum 9 above the core 8a, and the shielding core upper mechanism 14 having a dipped plate 12 and a joint shell 13 is attached to the shielding plug 11. It is installed vertically so as to be immersed in the coolant of the outlet plenum 9.

An inner cylinder 17 is provided inside the furnace vessel 3, and as shown partially enlarged in FIGS. 2 and 3, this inner cylinder 17 has an outlet nozzle 2a of the outlet pipe 2 and a A flow hole 15 is provided at a slightly lower position facing each other, and a flow hole group 16 is provided above the flow hole 15, which has a hole diameter larger than that of the flow hole 15 and whose number gradually decreases from the upper row 16a to the lower row 16d.

The inner cylinder 17 provided with the flow holes 15 and the flow hole group 16 is erected inside the furnace vessel 3 and fixed to the support plate 5a.

Note that a guard vessel 18 is provided on the outside of the furnace vessel 3, and guard pipes are provided in the inlet pipe 1 and the outlet pipe 2, respectively. A fuel exchanger for replacing the fuel assembly 8 of the reactor core 8a6- is disposed in the reactor vessel 3 with a shield plug inserted therein.

In the above configuration, during reactor operation, temperature fluctuations between the low-temperature sodium flowing out from the flow hole 15 during scram and the high-temperature sodium flowing between the inner cylinder 17 and the reactor vessel 3 affect the flow hole group. The flowing sodium reduces the temperature difference.

Therefore, according to the present invention, the inner cylinder 1 provided inside the furnace vessel 3
7 is provided with a flow hole 15 having a smaller diameter than the conventional flow hole, and a group of flow holes 16 having a larger diameter is provided above the flow hole 15. Therefore, the temperature fluctuation of the outlet nozzle portion 2a and the axial temperature gradient of the furnace vessel 3 are reduced, thereby reducing the thermal stress of the structural material.

Note that the present invention is not limited to the above-mentioned embodiments, and for example, the number and arrangement of holes provided in the flow hole group 16 can be arbitrarily set based on the ratio of the number of holes and the hole diameter of the flow holes 15 provided below. can do.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing all parts of an embodiment of a fast breeder reactor according to the present invention, FIG. 2 is an enlarged sectional view of the main part of FIG. 1, and FIG. FIG. 2 is a perspective view showing a further enlarged main part. DESCRIPTION OF SYMBOLS 1... Inlet piping, 2... Outlet piping, 3... Reactor vessel, 4... Core support structure, 5... Support plate, 6...
Inlet plenum, 7... Blanket fuel assembly, 8.
... Core fuel assembly, 8a... Core, 9... Outlet plenum, 1o... Cover gas, 11... Shielding plug, 12... Dirubbed plate, 13... Joint shell, 1
4... Core upper mechanism, 15... Flow hole pe 16
...Flow hole group, 17...Inner cylinder, 18...Guard container, 19...Guard pipe, 2o...Fuel exchange machine. Patent Attorney Kikuchi, 5th Division Procedural Amendment (Format), 8ra5J・2. π2゜Mr. Haruki Shimada, Commissioner of the Japan Patent Office, Indication of Case 1982 Patent Application No. 1.3'2099 No. 2,
Title of the invention: Liquid metal cooled fast breeder reactor 3, Relationship to the amended person's case Patent applicant's address: 72 Horiyo-cho, Saiwai-ku, Yosaki-shi, Kanagawa Prefecture, Trap 1'
Base, A ship (307) Tokyo Shibaura Electric Co., Ltd. (and others 1
Name) 4. Agent 5. Date of amendment order: January 26, 1980 (shipment date) 6. Number of inventions increased by amendment 7. Figures 2 and 3 of the drawings subject to amendment 8. Revise the drawing as per the attached sheet.

Claims (2)

[Claims] (1) In a liquid metal cooled fast breeder reactor in which an inner cylinder is provided in an upper plenum in the reactor vessel and a plurality of flow holes are provided in the side surface of the inner cylinder, the liquid metal cooled fast breeder reactor is characterized by: type fast breeder reactor. (2) The flow hole group has a larger hole diameter than the flow holes provided near the outlet nozzle, and the number of holes gradually decreases from the upper row to the lower row. Liquid metal cooled fast breeder reactor according to item 11.