JPH0220718Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an improvement in the shipping can of a shipping device used to detect the presence or absence of damage in a nuclear fuel assembly.

In nuclear fuel assemblies used in nuclear reactors, some fuel rods may become damaged or pinhole due to continuous operation of the reactor, causing fission products generated inside to leak out. Even if such fuel assemblies still have some life remaining, they cannot be used for safety reasons, and therefore it is difficult to know which fuel assemblies are damaged or not. It is necessary and regular inspections of fuel assemblies are carried out.

This inspection is generally carried out by storing the fuel assembly in a storage pool, but if the fuel assembly cannot be confirmed with an underwater television camera, shipping means as shown in Fig. 1 is usually adopted.

That is, as shown in Figure 1, there is an electric heater h around the
A shipping can a equipped with an air jacket b containing a fuel assembly is placed in a storage pool P, a fuel assembly n to be inspected is stored in the shipping can a, and a jacket gas (usually nitrogen gas) is injected into the surrounding air jacket b. A heat insulating layer is formed by expelling the pool water inside, and due to the action of the heat insulating layer, the internal gas is thermally expanded due to self-heating of the fuel composition of the assembly, causing it to leak from the damaged part of the cladding.
This is carried away by carrier gas (same as jacket gas) fed from the bottom of the can, and radiation detector B detects the amount of radioactivity to check for damage.

However, some fuel assemblies n that have been stored for a long time in the storage pool P have reduced self-heating ability, and in that case, the electric heater h in the air jacket b is energized and the fuel is supplied through the air jacket b. The assembly n is forcibly heated to promote leakage of fission products.

By the way, conventional heating means are fixed to the inner wall of air jacket b, which has a double can, and cannot be removed without breaking the can, so maintenance such as testing insulation, repairing damaged parts, and cleaning is difficult. The problem is that it is almost impossible to do.

Therefore, this idea was devised in view of the above-mentioned circumstances.The heating means can be easily installed and removed without damaging the main body of the can, and maintenance can therefore be carried out regularly, allowing for long-term use. This system provides a shipping can that can withstand high temperatures, and consists of an outer can, an inner can, and a jacket chamber formed between both cans, with a heating member disposed in the jacket chamber, and a nuclear fuel assembly housed in the inner can. heats the body to leak fission products,
In a shipping device configured to detect the presence or absence of damage, elongated holes of a required length are provided in the four periphery portions of the bottom plate so that the peripheral surface of the inner can is located approximately at the center in the longitudinal direction, and the heating member is formed by a substrate slightly larger than the elongated hole and a plurality of heating wires set upright on the substrate at a required height, and the heating wires are attached to the circumferential surface of the inner can via each elongated hole, and the upper end thereof is is supported by a strip spring, and the board is detachably attached to the lower surface of the bottom plate by a stopper member.

Embodiments of this invention will be described below with reference to the drawings.

Although Fig. 2 does not show the upper half of the shipping can, 1 is made of stainless steel, has a rectangular cross section, and is surrounded by an outer can 1a and an inner can 1b forming a double can. , At the upper end, in order to take in and take out the fuel assembly n, a roof-shaped cap with a vertical temperature sensor S for adjusting the calorific value of the heating member, similar to the conventional product shown in Fig. 1, can be opened and closed by a cylinder mechanism. The jacket chamber 2 is installed between the outer can 1a and the inner can 1b.
It is filled with pool water at all times, but during shipping, the required amount of jacket gas is pumped through the conduit (Figure 1) to expel some of the pool water from the bottom and form a heat insulating layer. is being done.

By the way, in this invention, the bottom plate 3 welded to the bottom of the shipping can 1 is provided with a central hole 3a for introducing pool water and carrier gas into the can as shown in Fig. 3A. On all four sides of the periphery, wide elongated holes 3b are formed along each side of the inner tube 1b of the can, shorter than each side, and with the surface of each side passing approximately through the center as indicated by diagonal lines in the figure. A plurality of elastic clamping tools 4 divided into two or three parts as shown in Figure C are attached to the lower surface of both the inner and outer edges of each elongated hole 3b, and a plurality of elastic clamping tools 4 are attached to the surface of each side of the inner can 1b from the lower end. Almost 1/ of the tube
A plurality of strip springs 5 each having a concave and convex shape are installed substantially horizontally at three height positions.

In addition, FIG. 3B shows a heating member consisting of a heating wire 6 and a substrate 7, and the heating wire 6 covered by the sheath tube is placed in an inverted U shape about 1/3 of the height of the inner can 1b.
A plurality of them (three in the figure) are arranged in parallel in the longitudinal direction of the substrate 7, and the substrate 7 is made of stainless steel, and is formed in the shape of a can. It has a large circumference, and at the four corners of its upper surface are provided stoppers 7a that engage with elastic clamping members 4 provided on both inner and outer edges of the elongated hole 3b.

Therefore, the heating wires 6 arranged in parallel from below are inserted into the four elongated holes 3b of the bottom plate 3 as shown by the dotted arrows, and the heating wires 6 are placed along the circumferential surface of the inner can 1b, and the bent upper ends of the heating wires 6 are As shown in FIG. 4, the retainers 7a on the upper surface of the board 7 were inserted into the recesses of the strip springs 5 provided on each peripheral surface as shown in FIG. The heating members are engaged with the elastic holding members 4, and thus the heating members can be easily attached and detached along the circumferential surface of the inner can 1b as shown in FIG.

In addition, in Fig. 2, 11 is a pipe for supplying carrier gas during the can, 12 is a pipe for removing water from the can at any time in order to detect water-soluble radioactivity, and 13 in Fig. 3 is a pipe for supplying carrier gas during the can. This is a cord for connecting the heating wire to the power source.

Therefore, when the nuclear fuel assembly n whose self-heating effect has deteriorated due to long-term storage is stored in the inner can 1b, jacket gas is forced into the jacket chamber 2 to properly remove the water in the chamber. When a gas layer is formed and the surrounding heating wires 6 are energized to generate heat, the temperature inside the jacket chamber 2 rises, and through this the nuclear fuel assembly n in the inner can 1b flows into the pool water. As the fuel rods are heated, the internal pressure of the fuel rods increases, and the fission products generated inside leak out from the damaged area, and are transported toward the radiation detector by the carrier gas supplied from below. taken away.

After such a certain period of use, when inspecting the heating member, remove the nuclear fuel assembly n from the inner can 1b and empty the shipping can 1.
This can be hoisted by a crane or the like, the board 7 connected to the bottom plate 3 via the stoppers 4 and 7a on the ground can be removed, and the heating wires 6 can be pulled out from the four elongated holes 3b, respectively.

Then, after checking the quality of the insulation and the presence or absence of damage, if necessary, replace it with a new one, and then reassemble it to the inner can 1b as described above.

Although a fitting type member is shown as the fixing member for the bottom plate 3 and the substrate 7, the present invention is not limited to this, and other means may be used as long as it is removable.

As described above, according to this invention, the heating member can be easily installed and removed, and it is possible to inspect the insulation condition and whether there is any damage, as well as to clean it.
It is suitable for long-term use and can improve the heat generation effect of the fuel assembly.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a conventional shipping device. FIG. 2 is a sectional view with the upper half of the embodiment of this invention omitted. Figure 3A is a perspective view of the bottom plate. Figure B is a perspective view of the heating member. Figure C is a side view of the stopper member. FIG. 4 is a perspective view of a part of the inner can. In the figure, 1... Shipping can, 1a... Outer can, 1b... Inner can, 2... Jacket room,
3... Bottom plate, 3a... Center through hole, 3b... Long hole,
4... Elastic clamping tool, 5... Strip spring, 6... Heating wire, 7... Board, 7a... Stopper.

Claims (1)

[Scope of utility model registration request] It consists of an outer can 1a, an inner can 1b, and a jacket chamber 1c formed between both cans, and a heating member is disposed in the jacket chamber 1c to heat the nuclear fuel assembly n accommodated in the inner can 1b. In a shipping device that leaks nuclear fission products and detects the presence or absence of damage, a required length is provided around the four sides of the bottom plate 3 so that the peripheral surface of the inner can 1b is located approximately at the center in the longitudinal direction. A long hole 3b of the same size is provided, and the heating member is inserted into the long hole 3b.
It is formed by a slightly larger substrate 7 and a plurality of heating wires 6 erected on the substrate at a required height, and the heating wires 6 are attached to the circumferential surface of the inner can 1b through each elongated hole 3b, and the upper end thereof is attached. The shipping can is characterized in that the base plate 7 is supported by a strip spring 5, and the base plate 7 is detachably attached to the lower surface of the bottom plate 3 by means of stoppers 4 and 7a.