JPH0424151B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a channel used to transport spent fuel generated after long-term operation from various types of nuclear power plants, research and commercial nuclear reactors to reprocessing plants. The spent fuel mentioned above falls under the category of fissile cargo,
For transportation, aluminum baskets are used in which square holes (lodgements) are formed by arranging hollow rectangular channels made of boron-containing stainless steel with neutron-absorbing properties and casting them into aluminum. After cooling the spent fuel in a storage pool for a certain period of time, it is stored in a lodgement.
This basket is used as an internal material and is housed in a transport container designed and manufactured with due consideration to the safety of land and sea transport. The channel contains spent fuel and serves as a strength member and neutron absorber. In addition to the above, channels may be used as pool racks for long-term storage of spent fuel, in which case they serve as vertical retention and neutron absorption of the spent fuel. Conventionally, the methods for producing thin, rectangular, and long channels are two methods: one is to weld a round pipe and then make it into a square cross section by drawing, and the other is to form a half section into a conical cross section by bending. A commonly used method is to join two pieces together and weld them together.
However, in the channel for spent fuel that is the object of the present invention, the thin plate material is limited to boron-containing stainless steel plates, and this steel plate has low elongation and is not suitable for bending or plastic working. However, both methods fail because they do not meet the product specifications that require corrosion resistance of the same type of stainless steel that does not contain boron. Another option is to manufacture the channel by welding without processing the thin plate, but if a normal welding rod is used, the welded part does not contain boron, so neutron absorption performance in that part cannot be expected.
Since there is no other demand for boron-containing welding rods, they are not available on the market and cannot be obtained unless specified, and even if they are available, their welding technology and performance have not been confirmed. The present invention has been made to solve the problems associated with the above-mentioned processing and welding of conventional manufacturing techniques. It is characterized by the fact that the thin plates are arranged to form a rectangular cylinder, and the abutting parts of the thin plates are welded using non-filler and plasma welding. Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings and numerical examples. The boron-containing stainless steel plate used in the present invention preferably has C.0.04% or less, Cr16-19%, Ni8
-15% and B0.5-2% as main components, and an example of its composition is shown in the table below.

[Table] B ¹⁰ inB is 18.3% or more, B ¹⁰ is 0.0056g/
cm ² and is greater than the standard of 0.0032 g/cm ² . If the purpose is to increase neutron absorption performance, the amount of B can be reduced to approximately
A concentration higher than 0.9%, about 2%, is also possible, but in this case the difficulties involved in bending become even greater. The dimensions of the boron-containing stainless steel plate are 4 mm thick,
The width shall be approximately 200mm and the length approximately 1500mm. This thin plate is produced by making the plate through hot rolling and cold rolling processes, and then cutting it. As shown in Figures 1 and 2, 14 thin plates of boron-containing stainless steel are arranged on four sides using a jig, etc., and assembled into a long rectangular cylinder. As shown, at the corner where two adjacent thin plates 1 and 1 meet at right angles, one thin plate 1a abuts against the edge of the other thin plate 1b so that it slightly overlaps with the edge of the other thin plate 1b so that there is an extra thickness 1a', and the abutting surface The abutting portion 2 is made of non-filler, and the extra wall portion 1a' is welded and joined by plasma welding or gold welding to form an integral rectangular cylindrical channel 3. 5 indicates the position of the assembly and attachment portion of the basket 4. The welding conditions for non-filler and plasma welding are 1.
As an example, welding is carried out using DC positive polarity, a voltage of 15 to 25 V, a welding speed of 20 to 40 cm/min, and a current of 50 to 100 A. The orifice diameter is 1.8mm, and the orifice gas is
Ar99.99% is flowed at a flow rate of 1.5 to 2.0/min, shielding gas is Ar80%, H ₂ 20% is flowed at a flow rate of 13 to 17/min, and gas packing is performed by holding Ar99.9% for 15 minutes in one pass of a straight bead. Perform automatic welding. Bead height 4.20mm at the outer corner of the contact part shown in Figure 3
Then, Uranami appears in the 2.4mm width range of the inner corners of both sides. According to the manufacturing method of the present invention carried out as described above, the following actions and effects are achieved. A. When a boron-containing stainless steel plate is subjected to processing strain due to bending or plastic working, its corrosion resistance is significantly lower than that of ordinary stainless steel of the same type without boron. However, in the present invention, the four corners of the plate are Manufactured only by welding,
Although the number of welding steps increases, a decrease in corrosion resistance due to processing strain can be avoided. The corrosion resistance of this type of channel is determined by immersing it in pool water containing boric acid together with the spent fuel, but in the case of a basket, it may be subject to the corrosive effect of concentrated boric acid when dried after immersion, so the corrosion resistance of the channel is determined in relation to its lifespan. is important. B When welding using a welding rod, the neutron absorption performance of the weld is lacking, but in the case of the present invention, non-filler welding is performed, and boron is qualitatively stable during welding, so boron in the weld is A prismatic cylindrical channel with excellent neutron absorption performance without substantial deterioration can be obtained. C In the present invention, welding is performed by plasma arc welding, and the heat input is smaller than that of TIG welding, etc., and as a result, welding distortion is reduced and long rectangular cylindrical channels with high dimensional accuracy can be manufactured.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a boron-containing stainless steel channel manufactured by the method of the present invention, Fig. 2 is a side view showing the vertical cross-section in the upper half, and Fig. 3 is a mutual contact between thin boron-containing stainless steel plates. FIG. 4 is a cross-sectional view of the portion before welding, and FIG. 4 is a cross-sectional plan view showing the arrangement of channels manufactured according to the present invention in a basket. 1, 1a, 1b...Boron-containing stainless steel thin plate, 1a'...Excess wall portion, 2...Abutment location, 3...Square cylindrical channel, 4...Basket, 5...Assembly, mounting portion position.

Claims (1)

[Claims] 1. A method for manufacturing a boron-containing stainless steel channel, which comprises arranging thin boron-containing stainless steel plates to form a rectangular tube, and welding the abutting portions of the thin plates to each other by plasma welding using a non-filler.