JPS5988693A - Method of making nuclear fuel - 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 application of the invention] The non-invention relates to the production method of nuclear fuel, especially the island quality.

The present invention relates to a method for manufacturing fuel rods suitable for automated fuel manufacturing facilities that require high efficiency, sieve reliability, and maintainability.

[Prior art]

Figure 1 shows a cladding tube 1 plugged on one side with an end plug 4 and a fuel pellet 2. The fuel rod is shown filled with Dalenum Sring 3.

An example of a conventional fuel rod drying method is shown in FIG.

The fuel rods 5, which are filled with the fuel pellets 2 and which are unfilled, are aligned in the receiving section of the in-furnace carrying device 6. This carrying device runs on the rail 10 (2, enters the retort 7).

The furnace is a steel rettle]・7. Heater section 8. It is composed of a heat insulating section 9. When the fuel rods are carried into the furnace, the furnace is sealed, and the inside of the furnace is evacuated by the vacuum exhaust device 11 until the required temperature of A:9 degrees is reached.

When the inside of the furnace reaches a required degree of vacuum, it is heated by a heater 8 attached to the outer wall of the retort.

The heating temperature is 300C to 400t? , the holding time 101 is about 3 to 6 hours.

After this, it is sufficiently cooled by cooling in the furnace or by forced cooling using helium gas, etc., and then taken out from the furnace, temporarily plugged with end plugs, and sent to the next process (end plug welding).

In this conventional vacuum degassing method for fuel rods, the cladding tube is dried with pellets packed in it, which has poor efficiency and thermal efficiency.
Thermal expansion in a long furnace up to 5m long.

Disadvantages include poor quality of fuel rods such as straightness due to thermal distortion, and poor operability and maintainability due to larger reactors, making them unsuitable for high productivity and highly automated nuclear fuel equipment that will be required in the future. There is.

[Purpose of the invention]

The object of the present invention is to provide a highly efficient, reliable, and easy-to-maintain method for manufacturing nuclear fuel rods and to produce high-quality fuel by separately drying the transverse tubes and fuel pellets that form the nuclear fuel rods. It's about providing a framework.

[Summary of the invention]

The material of the cladding tube for fuel rods in reactors that use thermal neutrons, such as light water reactors and new converter reactors, has good corrosion resistance at high temperatures, and the uranium filled in the fuel rod and the cladding tube are Zircaloy, which is a zirconium alloy, is used for reasons such as good coexistence with neutrons and low neutron absorption. Although this Zircaloy has the above-mentioned advantages, it has the disadvantage that it absorbs hydrogen at high temperatures, and when the temperature drops, the combined mass of hydrogen and Zircaloy forms hydrogenated compounds locally.

Since the hydrogenated compound has a larger volume than the Zircaloy structure, when forming the compound, it causes excessive strain on the Zircaloy structure, and the compound itself is brittle, which poses a serious problem in terms of strength.

In a light water reactor, the average temperature in the fuel rods is about 1400C, so the above phenomenon is thought to occur. As a countermeasure, the moisture in the fuel rods is reduced as much as possible to prevent the generation of hydrogen at high temperatures.

In the process of forming fuel pellets to be filled into fuel rods without trenches, the pellets are naturally dried at high temperatures. Next, the fuel pellets are filled into the Ti tube and heated in a vacuum degassing drying furnace to approximately 300 t:' to 400 C, mainly to remove moisture.

However, this conventional method has the following drawbacks.

(1) The gap between the cladding tube and the pellet is very small (average 230μ in a light water reactor), and since the cladding tube is long at about 4 m, it takes a long time to reach the specified moisture content, which reduces production efficiency and thermal efficiency. bad.

(2) Since the furnace and reactor internals are as long as 5 m, thermal expansion and thermal distortion at high temperatures are large, which adversely affects the quality of the JlG straightness of the fuel rods.

(3) Since the furnace for fuel rods and the equipment for carrying them into the furnace are enlarged, the maintenance, maintenance, and operability of the equipment are poor, resulting in a decrease in production efficiency.

(4) Because it is a long reactor, it is economically advantageous to increase the throughput at one time, and from the viewpoint of space efficiency, it processes the number of fuel rods determined by the critical limit amount at one time. However, if the furnace breaks down, productivity will be hindered.

However, future light water reactor fuel production facilities will require automated facilities with higher production efficiency in order to increase production volume, and A, TR, and pluthermal fuel production facilities will require higher productivity and radiation exposure prevention.

For this reason, since the conventional vacuum descaling drying furnace has the above-mentioned drawbacks, an alternative drying method has become necessary.

Therefore, by drying the fuel pellets immediately before filling, drying the moisture in the cladding tube in a separate dedicated furnace, and performing the filling operation in a dry atmosphere, a new technology for nuclear fuel that compensates for the above drawbacks and provides pellets with even higher dryness. This led to the invention of the drying method.

[Embodiments of the invention]

An embodiment of the present invention will be shown below.

FIG. 3 shows a top view of a nuclear fuel rod manufacturing apparatus for drying nuclear fuel and filling a cladding tube according to the present invention. Covering'#1
The pellets 2 to be filled are arranged in a pellet tray 20 and placed in an air-helicum exchange chamber 21 having a shutter at the exit.

Here, the air atmosphere is replaced with a helium atmosphere using a vacuum device. When this is completed, the shutter on the exit side is opened and the product is carried into the helium atmosphere glove box 12. A pellet drying oven 13 is installed above the glove box 12. Here, the beret 2, which has been dried together with the dish, further advances in the direction of the arrow until it reaches the place where the beret is filled [140].

On the other hand, after the cladding tube 1 is received in the receiving device 18, the shutter 1
7 is opened and carried into the cladding tube drying device 16. When the loading is completed, the shutter 17 is closed. At this time, the shutter 15 is closed.

This situation! By blowing hot air from one direction in the river, moisture can be easily removed from the inner and outer surfaces of the cladding.

When drying is completed, the atmosphere inside the apparatus is replaced with helium gas from air.

When the replacement is completed, the shutter 15 is opened and the cladding tube is pushed out into the glove box 12. Here, pellet filling device 1
Step 4 fills the cladding tube 1 with the pellets 2 on the pellet tray. It is also possible to drive a temporary end plug to seal the fuel after filling.

FIG. 4 shows a view taken in the direction of the arrow in FIG. 3.

FIG. 5 shows a cross-sectional view of FIG. 4.

The pellets 2 are arranged on a pellet plate 20. Since the pellets are arranged on the pellet plate 2° in lengths divided into about 10 parts with respect to the length to be filled into the cladding tube, the size of the pellet plate 2o is approximately 400 m x 400 mm. This pellet plate 20 has a V-shaped groove formed therein, and the pellet is housed in the V-shaped groove. A plurality of stacked pellet plates are transferred to a pellet plate transfer trolley 25 that moves on rails 26 to 1) the position of the pellet drying oven 13;

Here, the pellet drying oven 1 is moved by the pellet tray lifting device 22.
3 will be brought in.

This drying oven has a retort 7, a heater 8. A heat insulating material 9° and a vacuum evacuation device 11j, j7+J# are required, but since the pellet plate is relatively small in size, a general-purpose furnace will suffice.

The heating temperature is the same as the conventional type, but the time required for vacuuming, heating, holding, and cooling is reduced by about 60% when processing the same amount of pellets because the heat container for the object is not large. It is Noh.

Furthermore, since only the pellet plate is carried into the furnace, there is almost no need to consider the effects of heat as in the conventional type.

The dried pellets are taken out from the drying oven and transferred to the pellet filling section 144.

FIG. 6 is a detailed view of the pellet filling section 14.

The pellets 2 arranged on the pellet plate 20 are filled into the cladding tube by a pellet gun shear 27 installed parallel to the grooves of the pellet plate.

〔Effect of the invention〕

In the present invention, instead of drying the fuel rods together with the coating and a before sealing them, each fuel rod is efficiently dried immediately before filling, and the filling and sealing is performed in an atmosphere where the dry state can be maintained. A manufacturing method is provided.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a nuclear fuel rod, Figure 2 is a cross-sectional view of a conventional example,
3 and 5d: explanatory diagrams of an embodiment according to the present invention, FIG. 4 is a view taken in the direction of arrow A in FIG. 3, and FIG. 6 is a partially detailed diagram. ■...Claying tube, 2...Fuel pellet, 3...Glenum ring, 4...9m plug, butt...Fuel rod, 6...
... Furnace loading device, 7... Retort, 8... Heater section, 9... Heat insulation section, 10... Rail, 11... Vacuum exhaust device, 12... Helium atmosphere glove box, 13...Bellet drying oven, 14...Bellet filling device, 15...Shutter, 16...Claying tube drying device, 17...Shutter, 18...Receiving device, 19
... Frame, 2o...Bellet plate, 21...2ki-
fart! , lum [! Chamber, 22...Bellet plate lifting device, 23...Guide, 24...Screw, 25
... Helle Nnl trolley, 26 river rail, 27...
Beret Gutusha. 1st ward nest 2 mouths ($4-mouth 3 ¥5 Figure ζ9 Otsushi)

Claims (1)

[Claims] 1. After welding an end plug to one end of the metal cladding tube,? In the manufacturing method of nuclear fuel rods, which are manufactured by filling M several fuel pellets, replacing the internal gas with pure residue, and finally sealing the other end of the cladding tube with an end plug, the fuel pellets and the metal cladding are It is characterized by providing a late drying device (6) for drying each separately before filling, and connecting the drying devices with a container containing a dry atmosphere such as pure waste, and filling and sealing the fuel pellets in this container. A method for producing nuclear fuel.