JPS59179773A - Heat treatment for producing composite cladding pipe for nuclear fuel - Google Patents

Abstract

PURPOSE:To produce a composite cladding pipe for nuclear fuel consisting of a soft Zr liner and an external pipe having high strength by subjecting the composite cladding pipe consisting of the external pipe composed of a zircaloy and an internal pipe composed of a Zr liner to a final heat treatment in an adequate temp. region. CONSTITUTION:A composite cladding pipe 1 for nuclear fuel to be loaded therein with a nuclear fuel 4 is formed by forming an external pipe 2 consisting of a zircaloy added with a small amt. of Sn, Fe, Ni, etc. to Zr and an internal pipe 3 consisting of a Zr liner by rolling such as explosive binding or the like then subjecting the pipe to a heating treatment in the temp. region where the temp. is higher than the stress relief annealing temp. region of the zircaloy, the decrease in the strength thereof is as small as possible and the strength of Zr can be decreased down to the strength as approximate as possible to the strength of Zr in the perfect annealing temp. region of the zircaloy, in the final stage. The pipe 1 consisting of the zircaloy external pipe 2 having high strength and the internal pipe 3 consisting of the soft Zr liner is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a nuclear fuel composite cladding tube, which is formed by lining a zirconium liner on a nuclear fuel element which is a component of a nuclear fuel assembly, and in particular on a zircaloy sheathing tube. This relates to improvements in the heat treatment method used as the final step.

The nuclear fuel composite cladding tube 1 as described above is lined with an outer tube 2 VC and an inner tube 3 as shown in FIG.
tti, / ruconium (Zr) Vc small amount of tin (Sn
), iron (Fe), nickel (N1), etc. are added to Zircaloy, in addition to its original property of low neutron absorption.
Zr itself is used as a zirconium liner in the inner tube 3, and at this time, the nuclear fuel 4 loaded into the cladding tube IK is In view of this, the softer the zirconium liner, the more effective it is, whereas the Zircaloy sheath tube 2 is required to have considerably greater strength.

In other words, in the case of a boiling water reactor (BWR), the coolant pressure is about rri7oi5, and in the case of a pressurized water reactor (
PWR) VC is expensive at 157 mm, so it must be strong enough to withstand such pressure, and if it is not strong enough, it may buckle due to the pressure of the coolant during use. , causing creep buckling and failure of the fuel element.

By the way, the nuclear fuel composite cladding tube 1 is produced by forming a composite cladding tube by processing both tubes 2 and 3 by rolling means such as explosive coupling and tube reduction processing until they are lined with the required dimensions. In order to soften the zirconium that has been hardened by rolling, the composite cladding tube is subjected to heat treatment.

However, the conventional heat treatment method described above focuses only on the softening of zirconium, and heats it in a temperature range of 550 to 580'C.

However, it cannot be said that the nuclear fuel composite cladding tube obtained through the heat treatment described above necessarily exhibits sufficient strength when used in PWRfX, etc., and as a result of considering this point, the above-mentioned 550 ~580°C, as understood from the strength characteristic curves A and B of Norcaloy and zirconium versus heat treatment temperature shown in FIG.
This corresponds to the complete annealing temperature range T2 of Zircaloy, and therefore, of course, through the heat treatment, Fluconium becomes sufficiently soft like B, and at the same time, Norcaloy also becomes as strong as A. The fact that it has deteriorated (konaru).

The present invention is based on the above-mentioned studies, and is based on the heat treatment performed in the final process in the production of nuclear fuel composite cladding in an appropriate temperature range. The project aims to make it possible to obtain a "nuclear fuel" element using tubes, and its characteristics are:--A composite cladding tube is formed by lining a zirconium liner on a Norcaloy sheathed tube by conventional methods such as rolling. After that, the composite cladding is heated at a temperature higher than the strain relief annealing temperature range of Zircaloy, the strength decrease is as small as possible, and the strength of zirconium is higher than that of fluoronium in the complete annealing temperature range ζ of Norcaloy. The heating is carried out in a temperature range that can reduce the strength to a high strength as close to the strength as possible.

Here, the heat treatment temperature-strength characteristic curves A and B shown in Figure 2 above change depending on the degree of work in rolling, and B changes depending on the oxygen content of zirconium, but the difference between zircaloy and zirconium is have differences such as A and B,
Therefore, in the strain relief annealing temperature range T1 of Zircaloy, which is usually 450 to 490°C, B drops rapidly and zirconium becomes soft.
Thick.

Therefore, in the present invention, the temperature range is higher than the above-mentioned temperature ranges T, &, and is considerably lower than the temperature range T2, preferably the temperature range T indicated by diagonal lines in the figure.

The material is then heat-treated.

That is T. In the region of It has extremely high strength compared to the strength.

This difference occurs because zirconium (zirconium) has high purity and no impurities, so it begins to crystallize quickly, whereas in Norcaloy, which has alloying elements added, it begins to crystallize more slowly, causing differences in crystal structure and grain size.

As mentioned above, the temperature range 'ro varies depending on other factors such as processing degree and has a property that cannot be specified as a numerical value, but it is approximately 490 to 510°C, and this temperature range is T1 and T2. The heat treatment furnace has a narrower range of ±5
It can be controlled industrially at ℃ without any problems.

According to the present invention, as described above, the heat treatment temperature is set to an appropriate temperature, so the softness required of the zirconium inner tube is slightly less than that of the conventional method.
In addition to being able to have sufficient flexibility, Norcaloy, which is a lined tube, has about 15 times the strength of the conventional method and the same strength as the cladding tube conventionally used for PWH. and can provide highly reliable nuclear fuel elements.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a nuclear fuel composite cladding tube, and FIG. 2 is a chart showing strength characteristic curves of Norcaloy and zirconium with respect to heat treatment temperature. 1... Exterior tube T1... Norcaloy strain relief annealing temperature range T2...
・Norcaloy complete annealing temperature range 'ro...temperature range

Claims (1)

[Claims] After forming a composite cladding tube with a Zircaloy sheathed tube lined with a zirconium liner by a conventional method such as rolling, the composite cladding tube is heated at a temperature higher than the strain relief annealing temperature range of Zircaloy to improve its strength. The decrease is as small as possible,
A nuclear fuel composite cladding tube characterized in that the strength of zirconium is heated in a temperature range where the strength of zirconium can be reduced by high-strength cutting as close as possible to the strength of zirconium in the complete annealing temperature range of Zircaloy. Heat treatment method for manufacturing.