JPH01301830A - High corrosion-resistant zirconium alloy - Google Patents

Abstract

PURPOSE:To obtain a Zn alloy having excellent corrosion resistance in water and steam at high temp. and high pressure by incorporating one or more kinds of specific amounts of Nb, V, Mo, Ta and W into a Zn-Sn-Fe-Cn-Ni alloy or a Zn-Sn-Fe-Cr alloy. CONSTITUTION:As the material such as a fuel covering tube and a core structural material of a boiling-water reactor and a pressurized-water reactor used in water and steam at high temp. and high pressure, a Zr alloy having the comspn. contg., by weight, 0.5-1.7% Sn, 0.05-0.5% Fe and 0.05-0.3% Cr, furthermore contg. total 0.005-0.5% of one or more kinds among Nb, MO, W, V and Ta and the balance Zr, or a Zr alloy having the above compsn. and the which <=0.1% Ni is furthermore added and incorporated is used. The Zr alloy having excellent corrosion resistance in an environment where it is brought into contact with high temp. and high pressure-water and steam can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to a zirconium alloy having high corrosion resistance, particularly a zirconium alloy suitable for use in high temperature, high pressure water or steam, such as in a nuclear reactor.

(Prior art and its problems) Zirconium alloys are used in boiling water reactors (BWRs) and pressurized water reactors (PWRs) because of their suitable mechanical properties, small thermal neutron absorption cross sections and good corrosion resistance. Used for fuel cladding, reactor core structural materials, etc. Typical alloys that have been used for such purposes include Zircaloy-2 (JIS ZrTN802D) and Zircaloy-4 (JIS ZrTN804D), as well as Zr-Nb alloys (for example, as pressure tubes in CANDU furnaces). Zr-2,5Nb alloy, which has a proven track record, is also used.

Corrosion of zirconium alloys initially begins with the formation of an oxide film that is black and has a uniform thickness.

In the case of the boiling water reactor (BWR), so-called "nodular corrosion" in which white nodular oxides grow on the black, uniform oxide film progresses. In contrast, nodular corrosion does not occur in a pressurized water reactor (PWR), but progresses in the form of an increasing thickness of a uniform corrosion film.

Among the above two types of corrosion progression forms, uniform corrosion in PWRs has not been viewed as a particular problem under current PWR operating conditions. However, in recent years, plans have been proposed to extend the useful life of zirconium alloy members in the reactor in order to further increase the burn-up of the fuel and improve economic efficiency. As a result, concerns have arisen regarding the uniform corrosion resistance of zirconium alloy members, which had not been seen as a problem under current usage conditions.

In other words, Zircaloy-4 used in PWRs has good uniform corrosion resistance under current operating conditions and has not caused any major corrosion problems, but in harsh environments considering the extension of the fuel usage period mentioned above, it has good uniform corrosion resistance. It has been found that corrosion progresses rapidly and is difficult to suppress within permissible limits.

As a method for improving uniform corrosion resistance, Zr −
A method has been proposed (Japanese Unexamined Patent Application Publication No. 170552/1983) of processing an Nb-Sn alloy with a third element such as Fe5Cr, Mo, ■, etc. at a relatively low temperature. However, this method does not provide sufficient uniform corrosion resistance because the amount of Nb added is too large.

An object of the present invention is to provide a zirconium alloy that has sufficient corrosion resistance against uniform corrosion of the outer surface of a tube due to long-term high-temperature, high-pressure water (or steam).

(Means for Solving the Ll! Problem) The present inventors have investigated various zirconium alloys that have sufficient uniform corrosion resistance in environments exposed to high-temperature, high-pressure water (or steam) for long periods of time. Zr-5n-Fe-Cr-Ni system or Zr-S
Trace elements ■, Nb, MO are added to the n-Fe-Cr alloy.
One or more of sWs and Ta in total from 0.005 to 0
．． It has been found that uniform corrosion properties are dramatically improved by adding 5%. That is, the gist of the present invention regarding a highly corrosion-resistant zirconium alloy is as follows: Sn: 0.5-1.7%, Fe: 0.05-1.
0.5%, Cr: 0.05 to 0.3%, and further contains a total of 0.005 to 0.5% of one or more of Nb, Mo, W, V, and Ta, and the balance is Zr. It is a highly corrosion-resistant zirconium alloy characterized by consisting of unavoidable impurities.

Furthermore, if desired, Ni:O may be contained in an amount of 1% or less, preferably 0.01-0.1%.

In particular, the corrosion resistance provided by the alloy according to the present invention is significantly developed over a long period of time as resistance to uniform corrosion in high temperature, high pressure water environments such as those found in PWR.

This is a zirconium alloy that exhibits uniform corrosion resistance.

(Function) Hereinafter, the reason why the types and contents of the components in the alloy of the present invention were selected as described above will be explained together with the function and effect.

Sn: The corrosion resistance of Zr against uniform corrosion is degraded by nitrogen as an impurity. Sn is added to remove the adverse effects of nitrogen. However, the nitrogen level of recent Sponge Z has been suppressed to several tens of ppm, and care has been taken to minimize nitrogen absorption during the manufacturing process, so the Sn content can be lower than that of conventional Zircaloy. Therefore, the lower limit is set at 0.5%, where the effect of improving uniform corrosion appears.On the other hand, since adding a large amount deteriorates the corrosion resistance against uniform corrosion, the upper limit is set at 1.7%.

Fe: Fe is also effective in improving corrosion resistance against uniform corrosion. The lower limit is set at 0.05% at which this effect appears, and the upper limit is set at 0.5% to avoid adding a large amount that may have an adverse effect on cold workability.

Cr: The effects of Cr are almost the same as those of Fe. In order to obtain the effect of improving corrosion resistance, a content of 0.05% is required.

Since Cr tends to precipitate intermetallic compounds during heat treatment, the upper limit is set to 0.3%.

Ni: When Ni is added, even a small amount has a great effect on improving corrosion resistance against uniform corrosion. On the other hand, Ni incorporates hydrogen generated during corrosion into the alloy, contributing to hydrogen embrittlement. Therefore, if desired, it may be contained in an amount of 0.1% or less, preferably in the range of 0.01 to 0.1%.

Nb, Mo, W, V and Ta These elements have approximately equal effects on improving corrosion resistance against uniform corrosion. The effect appears with a fine 1 content of 0.005% each, and even if two or more types are added in combination, the same effect will be obtained if the total amount is o, oos% or more.

However, if the total content exceeds 0.5%, the effect of improving corrosion resistance will be saturated, and the neutron absorption cross section will increase and processability will deteriorate, so the upper limit of the total content is set to 0.5%.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) A number of alloys with varying contents of additive components were melted and their effects on corrosion resistance were investigated. The components of the sample materials are shown in Table 1.

Conventional material 1 is JIS ZrTN804D (Zircaloy-4
) Equivalent material, conventional material 2 is a JIS ZrTN802D (Zircaloy ~ 2) equivalent material. The basic conditions of the test are as follows. The corrosion test results are also listed in Table 1.

1. Production of test material (plate thickness 0.6 mm) ■ Approx. 700
A small ingot of g is made by button melting ■ β treatment 7 1050℃ x 30 minutes, water cooling ■ Hot working 2 650℃ ■ Intermediate annealing: 650℃ x 2 hours (cooling rate in the furnace: O, 1℃/sec) ■ Cold working: degree of working 70%, intermediate annealing 650℃,
Repeated twice ■ Final cold working: Working degree 85% ■ Strain relief annealing: 460°C x 1.5 hours, (furnace cooling rate: O, l'C/sec) 11, Test piece size: 20 mm W x 30 mm' Xo , 6 open 7
Processed and polished with #1000 paper, 45Vo
1. %11F-45Vol, %HNOi 50Vol
, %) 1, pickled with O.

;11. Corrosion test using steam autoclave, 400℃ x 105kg
f/c1w” x 5500 hours to examine the corrosion increase per unit area.Although the normal corrosion test for zirconium alloys is 72 hours, here the test time was increased to examine long-term corrosion resistance. Made it longer.

(The following is a blank space) (Effects of the Invention) As is clear from the test results of Examples, the corrosion resistance of the alloy of the present invention in long-term corrosion tests is extremely excellent. Therefore, this alloy greatly contributes to extending the life of equipment when used in parts used in environments exposed to high temperature and high pressure water or steam, such as fuel cladding materials for nuclear reactors.

Claims (2)

[Claims] (1) In weight%, Sn: 0.5-1.7%, Fe: 0.05-0.5%,
Contains Cr: 0.05 to 0.3%, and further contains 0.005 to 0.5% in total of one or more of Nb, Mo, W, V, and Ta, with the remainder being Zr and unavoidable impurities. A highly corrosion resistant zirconium alloy. (2) A highly corrosion-resistant zirconium alloy, characterized in that the alloy according to claim 1 further contains 0.1% or less of Ni.