JPS61175594A - Method of storing nuclear fuel aggregate - 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 (Field of Industrial Application) This invention relates to a method for storing fuel assemblies, primarily for pressurized water reactors.

(Prior art) A so-called canless type fuel assembly At:i for pressurized water reactors (Fig. 2A) A large number of fuel rods 1 like a mouth and more than ten guide thimble tubes for control rods. 2 and one hollow tube 3 for a measuring device placed in the center are arranged in a square arrangement, the lower end of the guide thimble tube 2 is attached to the lower nozzle 4 via an end plug, and several lattice-shaped spacers are arranged in the middle. 5, and the upper end of the guide thimble tube 2 is attached to the upper nozzle 6 without a cap.More than 100 such assemblies A are loaded in the reactor, and during operation, the guide thimble tube 2 is 2
The control rods hanging from the reactor body or the combustible absorption rod assembly B (this is arranged in the same number as the guide thimble tube 2 as shown in Fig. 3, and is filled with boron carbide pellets, which is a neutron absorbing material, inside) The upper ends of the combustible absorption rods 7 are tied together with a rectangular end plate 8, and a hollow tube (attached to a hanging rod 10) is inserted to control the fuel output. 3, a measuring device is periodically inserted to check the operating status of the furnace.

The fuel assembly A is then taken out of the furnace for periodic inspection every certain operating cycle (generally about one year), and the combustible absorption rod assembly B? In the inserted one, it is extracted from fuel assembly A, and fuel assembly A is placed in the storage pool in a storage rack (frame made of stainless steel profiles) designed and constructed based on the criticality of the current fuel rod enrichment. The slender cases with sides of 220 to 230 meters and height of about 5 meters are arranged in the front, back, left, and right directions at a pitch of about 500 meters. A method of reducing the volume of rod assembly B has been proposed, in which the combustible absorption rods are cut into short lengths and stored in a storage box in order to save space in a dedicated rack installed separately in the pool. .

(Problem to be solved by the invention) By the way, nuclear power plants that use pressurized water reactors have recently begun to operate on long-term cycles (1 year to 1.5
4), and along with this, the enrichment of fuel rods has increased from the previous 3 to 4 to 5 degrees.

Considering this situation, when storing new fuel, it is natural to use the conventional method of separating combustible absorber rod assemblies from fuel assemblies to store irradiated fuel assemblies in preparation for periodic inspections. If they were to be stored in racks, there would be a small margin for criticality control and safety would be lowered, and new storage equipment would have to be prepared that was commensurate with the concentration, which would be extremely uneconomical. As for the rod assembly,
First, creating a storage space separate from the storage rack for fuel assemblies increases the size of the pool, and second, using storage racks for fuel assemblies reduces the storage space for fuel assemblies. Therefore, in the 36th combustible intake-5
The method of cutting the storage rod short is not applicable to items that will be reused.

Therefore, the purpose of this invention is to make it possible to safely store fuel assemblies by using existing equipment without preparing new storage equipment, and at the same time, to store combustible absorption rod assemblies without requiring extra space. The objective is to provide a storage method for properly storing.

(Means for Solving the Problems) Based on the above object, the present invention provides a storage rack with a large number of squarely arranged fuel rods and more than ten guide thimbles in each case of a storage rack installed in a storage pool. A tube, a single hollow tube, a lower nozzle located at the lower ends thereof and attached to the guide thimble tube, several spacers in the middle, and an upper nozzle attached to the upper ends of the guide thimble tube and the hollow tube. The fuel assembly is characterized in that the combustible absorption rods of the combustible absorption rod assembly are inserted into all guide thimble tubes of each fuel assembly.

(Embodiment) Referring to FIG. 1, an embodiment of the present invention will be described. H is a storage rack for fuel assemblies installed in a storage pool, and H is a storage rack for fuel assemblies installed in a frame 11 and inside the frame. Like the conventional case 12, it is designed based on the criticality due to the enrichment (3%) of the fuel rods, and the frame 11 is assembled with vertical, horizontal and diagonal shapes made of stainless steel. The case 12 is also made of stainless steel and has a side of 2201111~2301m and a height of about 5.
It has a military rectangular elongated cylindrical body, and has approximately 5 mm in the frame 11.
A required number of them are arranged in the front, rear, left and right directions at a pitch of 0,011 m. Inside each case 12 are a large number of fuel rods arranged in a square arrangement 11 several guide thimble tubes 2. A hollow tube for a measuring device 3. Guide thimble tubes 2 located at their lower ends
Canless type fuel assemblies A are each accommodated, each consisting of a lower nozzle 4 attached to the lower nozzle 4°, several stages of lattice-like spacers 5 in the middle, and an upper nozzle 6 connected to the upper end of the guide thimble tube 2. The upper ends of the combustible absorption rods 7, which are arranged in the same number and the same amount as the guide thimble tubes 2, are bound to the ten or more guide thimble tubes 2 of the fuel assembly A with an end plate 8, and this end plate 8 is attached to a coil spring. A combustible absorption rod 7 of a combustible absorption rod assembly B connected to a hanging rod 10 via a rod 9 is inserted.

In this way, the combustible absorption rods 7 are inserted into all the guide thimble tubes 2 of the fuel assembly A housed in the case 12 of the storage rack H, so that the fuel for long-term cycle operation with increased enrichment can be used. The nuclear fission chain reaction of the fuel rods 1 due to the juxtaposition of the assemblies A is suppressed, and a large number of the fuel assemblies A are maintained in a subcritical state.

(Effects of the Invention) As described above, according to the present invention, when storing a canless type fuel assembly, the combustible absorption rods of the combustible absorption rod assembly are inserted into all the guide thimble pipes. Problems with criticality control have been resolved, and conventional storage equipment can be used as is for highly enriched fuel assemblies for long-term cycle operation, making it extremely economical. The fuel assembly can be stored in the same location as the fuel assembly, which eliminates the need for extra space and prevents the storage pool or facility from becoming larger, making it convenient for reuse. It has the following effects.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of an embodiment of the invention. Figure 2A is a front view of the fuel assembly. The opening in the figure is a plan view taken along the line X-X. FIG. 3 is a front view of the combustible absorption rod assembly. In the figure, 1... fuel rod, 2... guide thimble tube, 3...
... hollow tube, 4 ... lower nozzle, 5 ... spacer,
6... Upper nozzle, 7... Combustible absorption rod, A... Fuel assembly, B... Combustible absorption rod assembly, H... Storage rack.

Claims (1)

[Claims] In each case of storage racks built into the storage pool,
A large number of squarely arranged fuel rods, more than ten guide thimble tubes, one hollow tube, a lower nozzle located at the lower end thereof and attached to the guide thimble tube, and several spacers in the middle, an upper nozzle attached to the upper end of a guide thimble tube; and a combustible absorption rod of the combustible absorption rod assembly is inserted into all the guide thimble tubes of each fuel assembly. How to store fuel assemblies.