JPS58205889A - Nuclear fuel rod - 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] [Technical field of invention] The present invention relates to nuclear fuel rods for boiling water reactor equipment.

[Technical background of the invention]

A conventional nuclear fuel rod will be explained with reference to FIG.

2 in the figure is an elongated cylindrical cladding tube. This cladding tube 2
It is made of a zirconium alloy called Zircaloy. In the inner space of the cladding tube 2, uranium dioxide pellets 4, which are nuclear fuel made by sintering uranium dioxide into a cylindrical shape, are placed.
... are housed in a stacked manner. Above the uranium dioxide pellet 4... is F produced by the reaction of the pellet 4.
A plenum 6 is formed to store P gas. The upper and lower ends of the cladding tube 2 are sealed with an upper end plug 8 and a lower end plug 10, respectively. A Blenheim spring 12 is provided in the plenum 6, and the Blenheim spring 12 is configured to press the pellets 4 downward and hold them.

In boiling water reactor equipment, the nuclear fuel rods described above are combined in 8 rows and 8 columns to form a fuel assembly, and a large number of these fuel assemblies are housed in a reactor pressure vessel to form a reactor core. Ta.

[Problems with background technology]

The conventional nuclear fuel rods have the following problems when the reactor equipment becomes operational and gradually becomes hotter. That is, the coefficient of linear expansion of the pellets 4 is higher than that of the cladding tube 2 made of Zircaloy.
As the temperature increases, the gap between the side circumferential surface of the pellet 4 and the inner circumferential surface of the cladding tube 2 gradually becomes smaller, and eventually the cladding tube 2 comes to be expanded by the pellet 4. In such a state, tensile stress will be generated on the inner surface of the cladding tube 2. Also, pellet 4
Nuclear fission reactions produce corrosive fission products such as iodine. Therefore, the innermost peripheral surface of the cladding tube 2 was in a state where stress corrosion cracking was likely to occur, and there was a risk that cracks would occur.

If a crack were to occur in the cladding tube, the nuclear fuel material and fission products of the pellets 4 would leak and mix into the coolant, eventually leading to the shutdown of the nuclear reactor equipment.

[Purpose of the invention]

An object of the present invention is to provide a nuclear fuel rod that can prevent stress corrosion cracking by reducing the tensile stress acting on the innermost lining layer where stress corrosion cracking is most likely to occur during thermal expansion. There is a particular thing.

[Summary of the invention]

In the nuclear fuel rod according to the present invention, a lining layer made of a material having a coefficient of linear expansion larger than that of the zirconium alloy is provided on the entire inner surface of the zirconium alloy cladding tube, and the innermost periphery where stress corrosion cracking is likely to occur when thermally expanded is provided. This is designed to reduce the tensile stress applied to the lining layer.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 2 and 3. Figure 2 is a cross-sectional view of a nuclear fuel rod, with 10
2 is a cladding tube. The cladding tube 102 is made of a zirconium alloy and is formed into the longest cylindrical shape. A lining layer 10 is formed on the inner peripheral surface of the cladding tube 102 and is made of a material having a higher coefficient of linear expansion than the zirconium alloy, such as nickel. This lining layer 104 is in close contact with the inner peripheral surface of the cladding tube 102 at room temperature. The inner space of the lining layer 104 accommodates uranium dioxide pellets 106 as a nuclear fuel material similar to conventional ones. This uranium dioxide pellet 1
06 is pressed and held by a solenum spring as in the conventional case. The upper and lower openings of the cladding tube 102 are also sealed with upper and lower end plugs as in the conventional case.

Such a configuration works as follows.

That is, the pellets 106, which have become hot during operation of the nuclear reactor equipment, thermally expand and spread the cladding tube 102 and the lining layer 104. Therefore, tensile stress is generated in the cladding tube 102 and the lining layer 104. However, compressive stress is generated in the lining layer due to the difference in coefficient of linear expansion between the cladding tube 102 and the lining layer 104, and this compressive stress often reduces the tensile stress of the lining layer 104.

The generation of the compressive stress will be explained with reference to FIG. Here, each code is as follows.

d: Inner diameter of cladding tube 102 and outer diameter of lining tube 104 tl: Thickness of cladding tube 102 tc: Thickness of lining tube 104 EB: Young's modulus of cladding tube 102 Ec: Young's modulus of lining tube 104 αlI : Coefficient of linear expansion α of cladding tube 102 @ : Coefficient of linear expansion of lining tube 104 At this time, if the temperature rises from room temperature To to T, temperature difference ΔT = T − T.

Totoru. First, in an unrestricted state, the increase δdl in the inner diameter d of the cladding tube 102 and the increase δda in the outer diameter d of the lining layer 104 are δdl=π(d+ts)α−ΔT, where πdα, ΔT(',' d) tm) δda=yr(d+ta)αCΔT medium πdαCΔT (',"d>tc).α$〈
Since αC is δd, (δde, the cladding tube 102 is balanced in tension and compression in the lining layer 104Fi. Therefore, the amount of deformation of the cladding tube 102 when the pressure P from the inner space is acting is Δd
m, and the amount of deformation of the lining layer 104 is Δd.B=*(d+t*)xP(d+
t1)X±21s E.

becomes. Even after thermal deformation, the cladding tube 102 and the lining layer 10
Since it is in close contact with 4, it is 4yd of both types.

The relationship between δae and Δd−9Δd・ is δda+Δds=δdo−Δd.

becomes. Therefore, Pd(('mate)+(,,B,month=2ΔT(αC−αS)
becomes. At this time, the circumferential stress σC generated in the internal pressure cylinder to which the pressure P is applied from the inner space is as follows. In this formula, T T o ) OeαC-6m>
Since σ6>0, it can be seen that σC is compressive stress. This compressive stress σe td t o =0.05
1111 +tl=0.85*Ec=19.70
X 10” Kp/yd e E a= 6.97 x
10" KP/lJ mαa:=13.3 X 10
−” s” 1 depth 6.7
0 Kp/MJ.

The above has the following advantages.

First, the innermost lining layer 10 where stress corrosion cracking is likely to occur
The tensile stress acting on the cladding tube 102 and the lining layer 104 is offset and reduced by the compressive stress go generated in the lining layer 104 due to the difference in thermal deformation between the cladding tube 102 and the lining layer 104. Therefore, it is possible to reduce the tensile stress of the lining layer 104, where stress corrosion cracking is likely to occur, and prevent stress corrosion cracking.

Furthermore, since the inner surface of the cladding tube 102 is protected by a nickel lining layer 104, it does not come into contact with corrosive fission products generated from the pellets 106, and stress corrosion cracking of the cladding tube 102 can be prevented. can.

Note that the present invention is not limited to the above embodiment. For example, the lining layer 104 is not limited to nickel.
As shown in the table below, any material may be used as long as it has a coefficient of linear expansion larger than that of the zirconium alloy of the cladding tube 102.

Furthermore, the lining layer 104 can be shrink-fitted onto the cladding tube 102 so that compressive stress acts on the lining layer 104 even at room temperature.

〔Effect of the invention〕

According to the present invention, since the lining layer has a higher coefficient of linear expansion than the cladding, compressive stress is applied to the lining layer through thermal deformation, and this compressive stress reduces the tensile stress acting on the lining layer, resulting in stress corrosion. The effects are great, such as being able to provide a nuclear fuel rod that can prevent cracking and protect the innermost periphery of the cladding tube from corrosive products.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view of a conventional nuclear fuel rod, and FIGS. 2 and 3 are views showing an embodiment of the present invention.
The figure is a cross-sectional view, and FIG. 3 is a configuration diagram showing the dimensions of the cladding tube 102 and the lining layer 104. 102... Cladding tube, 104... Lining layer, 106...
- Nuclear fuel material, 8... Upper end plug, 10... Lower end plug. Sai 1 figure Sai 2 figure Rice 3 figure

Claims (2)

[Claims] (1) An elongated cylindrical cladding tube made of zirconium alloy,
A lining layer formed on the entire inner surface of the cladding tube with a material having a coefficient of linear expansion larger than that of the cladding tube, a nuclear firing material accommodated in the inner space of the lining layer, and openings at both ends of the cladding tube. A nuclear fuel rod characterized by comprising: an end plug for occluding the fuel rod; (2) The nuclear fuel rod described in the patent, wherein the lining layer is made of nickel. one