JPH02159336A - Nodular corrosion-resistant zirconium alloy - Google Patents

Abstract

PURPOSE:To improve the nodular corrosion resistance of the title alloy in the environment of being brought into contact with high temp.-high pressure water or steam by adding small amounts of Ru, Rh, Pd, Pt and Au to a Zr alloy contg. specific amounts of Sn, Fe and Cr. CONSTITUTION:The Zr alloy used in a nuclear reactor or the like is formed with, by weight, 0.20 to 1.70% Sn, 0.05 to 0.50% Fe, 0.05 to 0.30% Cr, total 0.005 to 3.00% of one or more kinds selected from Ru, Rh, Pd, Pt and Au and the balance Zr with inevitable impurities. If required, 0.01 to 0.10% Ni or furthermore 0.05 to 1.50% Nb are incorporated thereto. By the above compsn., nodular corrosion resistance satisfied under severe corrosive conditions can be obtd. Thus, corrosion resistance satisfied even in reactor primary water or the like can be shown.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a zirconium alloy having nodular corrosion resistance, particularly a nodular corrosion resistant zirconium alloy suitable for use in high temperature and high pressure water or steam environments such as in nuclear reactors. Concerning corrosive zirconium alloys.

(Prior art) Zirconium alloys have traditionally been used as core materials for light water reactor fuel cladding tubes, etc. due to their excellent properties such as a small thermal neutron absorption cross section, appropriate mechanical properties, and good corrosion resistance. . In particular, alloys that have been used commercially as fuel cladding include Zircaloy-2 (JIS 114
751 Zr TN 8020) and Zircaloy-4
(JIS H4751Zr TN 8040) alloy.

By the way, one of the problems encountered by these zirconium alloys in actual nuclear reactors is the problem of corrosion resistance. Particularly, in the reactor water environment of a boiling water reactor (BWR), an oxide film having a uniform thickness and a nodular oxide with a diameter of about 1 to 2 mm are formed on the outer periphery of the tube. The latter formation of nodular oxides is particularly called "nodular corrosion." Among these forms of corrosion, nogeller corrosion is viewed as a particular problem in maintaining the integrity of fuel rods because of its thick oxide film.

Several 4Ji measures have been proposed so far for the purpose of preventing such nogeller corrosion. For example, there are measures as described below.

(1) Zircaloy-2 or Zircaloy-4 (hereinafter referred to as Zircaloy-2 and A method of improving nodular corrosion resistance by changing the distribution, size, etc. of intermetallic compounds precipitated in Zircaloy-4.

This method uses intermetallic compounds (ZrC) in Zircaloy alloys.
This is based on the fact that the nogeller corrosion resistance of the zirconium alloy is improved when the zirconium alloys (ZrgNi-based compounds, ZrgNi-based compounds) are finely and uniformly distributed in the zirconium base material. However, in the method proposed by this proposal, it is necessary to add the troublesome process of performing one quenching treatment on the outer surface of the tube, which inevitably increases costs such as new equipment installation costs and inspection costs.

In addition, it is necessary to strictly control the heating temperature, cooling rate, etc. If heating above the (α + β) phase temperature and sufficient cooling rate are not ensured, nodular corrosion resistance cannot be improved. It cannot be said that the nodular corrosion resistance of the alloy has been sufficiently improved.

(2) Proposal of a new alloy Zircaloy-2 or Zircaloy-4 alloy with an additional 0.
There is an alloy (JP-A-60-36640) that contains 0.5 to 1.0% Nb to improve nodular corrosion resistance.

This alloy is a combination of a zirconium-niobium alloy, which has good nodular corrosion resistance, and a conventional zircaloy alloy, and shows a considerable improvement in nodular corrosion resistance. It cannot be said that the corrosion resistance has been sufficiently improved to the extent that the reactor fuel rods can be used for a long period of time.

(Problems to be Solved by the Invention) As described above, there is a growing need for improvements in nodular corrosion resistance under even more severe conditions.

Accordingly, it is an object of the present invention to provide a zirconium alloy that has better nodular corrosion resistance than conventional zirconium alloys.

(Means for solving the problem) As already mentioned in conventional Zircaloy alloys, Fe, Cr, N are added to improve nodular corrosion resistance.
i, etc., but it has been reported that nodular corrosion occurs in actual nuclear reactors. For example,
Even the Nb-added zirconium alloy mentioned above is subjected to a severe outside-furnace nodular corrosion resistance test (for example, 530°C x 105 kg/
d x 24 hours in water vapor), nodular corrosion could not be sufficiently suppressed.

Therefore, the present inventors conducted various studies and repeated experiments, and found that the above zirconium alloy contained Ru (ruthenium), Rh (rhodium), and Pd (palladium 1).
The present invention was completed based on the knowledge that the nodular corrosion resistance can be improved by adding one or more of , PL (platinum), and ^U (gold).

Here, in the present invention, Sn: 0.20 to 1.70% and Fe: 0.05 to 1.70% by weight.
0.50%, Cr: 0.05-0.30%, one or more selected from the group consisting of Ru, Rh, Pd, PL, and 80, total 0.005-0.005%
This is a nodular corrosion-resistant zirconium alloy consisting of 3.00% Zr and the balance Zr and unavoidable impurities.

According to a preferred embodiment of the present invention, Ni: 0.01 to
0.10% and/or Nb: 0.05-1.50%
It may be made to contain.

(Function) Next, the reason why the alloy composition is limited as described above in the present invention will be described. In this specification, "%" means "% by weight" unless otherwise specified.

Sn: The impurity nitrogen originally contained in sponge zirconium and the impurity nitrogen absorbed by the molten alloy from the atmosphere during the manufacture of the zirconium alloy have a negative effect on nodular corrosion resistance. The action of Sn eliminates this adverse effect. However, the amount of nitrogen in sponge zirconium is currently kept low at about 20 pp-, and the absorption of nitrogen gas during the manufacturing process is so low that it can be said to be almost non-existent due to considerations such as annealing in a high vacuum. Managed. Therefore, the lower limit of Sn added is 0.20% to fully exhibit its function. However, the effect of Sn is only to offset the negative effects of nitrogen, and Sn itself does not have the effect of improving corrosion resistance, and rather, adding a large amount of it actually causes deterioration. Therefore, considering the nitrogen level of current zirconium alloys, it is sufficient to set the upper limit to 1.70%.

Fe: Pe is an element that improves nodular corrosion resistance, and has the effect of improving nodular corrosion resistance as the amount added increases. The amount at which this effect is recognized is the lower limit, and it is 0.0
It is set at 5%. However, does Fe form an intermetallic compound with zirconium, and its size and distribution depend on the heat treatment conditions? jH
ft and affects nodular corrosion resistance. Therefore, adding a large amount may unnecessarily increase sensitivity to heat treatment, and may also lead to poor cold workability.
Considering the above, the upper limit of the amount of Fe added is set to 0.50%.

Cr: Like Fe, Cr is an element that is effective in improving the nodular corrosion resistance of the alloy of the present invention, and the improvement effect increases as the amount added increases. Since the effect of adding Cr appears from about 0.05%, this amount is set as the lower limit. Like Fe, Cr also forms intermetallic compounds, which has the effect of increasing heat treatment sensitivity, and it is not desirable to add too much.Therefore, the upper limit is set to 0.30%.

Ni: Ni is a desired additive component in the alloy according to the present invention, and is effective in improving nodular corrosion resistance when added in small amounts. The lower limit showing the effect of its addition is 0.01%. However, the addition of Ni increases the rate at which hydrogen generated during corrosion reactions is absorbed into the base material, causing negative effects such as hydrogen embrittlement. Therefore, in the present invention, when adding Ni, the amount of Ni added is The upper limit is kept at 0.1θ%.

Nb: Nb is also a desired additive component in the present invention and is effective in improving nodular corrosion resistance. However, Nb has a large thermal neutron absorption cross section, and it is not desirable to contain it in too large a quantity. Therefore, the lower limit is set at 0.05%, where the effect of improving nodular corrosion resistance is achieved by adding Nb, while the upper limit is set at 1. .Reduce to 50%.

Ru, Rh5Rd, Pt5Au: At least one of these elements is added. It is believed that all of the alloys of the present invention have the same improvement effect on nodular corrosion resistance. Any of the additive elements can be selected, and two or more kinds can be added in combination.
Regardless of whether one type of additive is added or two or more types of additives are added, the effect of improving nodular corrosion resistance is shown from a total addition amount of 0.005%. Although the nodular corrosion resistance is improved by increasing the amount added, all of these elements are expensive elements, and the amount of hydrogen absorbed increases depending on their combination, so the upper limit is set at 3.00%.

Other unavoidable impurities include nitrogen, Si, etc., but there is no particular restriction as long as the amount of these impurities is at the level of a normal zirconium alloy.

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

Examples As shown in Table 1, alloys having compositions with various additive components were melted, processed into plates, annealed, and subjected to a nodular corrosion resistance test. The influence of components on nodular corrosion resistance was investigated.

The ingot was melted using an argon arc melting furnace, and a small ingot weighing about 500 g was melted.

The analytical values of each ingot composition are as shown in Table 1, and corrosion test pieces were taken after processing into plates according to the steps shown below.

Nao, for comparison Zircaloy-2 (JIS Zr TN
802D equivalent) and JitReka E4 (JIS Z
(equivalent to TN 8040) was prepared in the same manner and subjected to the same corrosion test.

(Processing process) ■Solution treatment 1050℃×2hr - water quenching ■Hot rolling 700℃ heating, rolling rate approx. 60% ■Intermediate annealing 650℃×2hr ■Cold rolling Rolling rate approx. 75%, approx. 1.5mm thickness■
Annealing at 650°C x 2br (test piece) After polishing the entire surface of a plate-shaped test piece with a thickness of 1.5+wm, a width of 20mIII, and a length of 30sn with vapor (1600 or more),
The surface was pickled, thoroughly rinsed with water, and then subjected to a corrosion test.

(Corrosion test) Temperature: 560°C Pressure: 105 kgr7cm” JIn time = 200 hours As a nodular corrosion resistance evaluation test method, 50
A common method is to evaluate corrosion resistance in high-temperature, high-pressure steam at 0°C or higher, but in this example, particularly severe conditions were chosen to evaluate the nozzle error corrosion resistance at 560°C and 105 kg.
f/cj, a 200-hour test was conducted, and the indular corrosion resistance was determined by visual observation of the focus of nodular generation.

The results are summarized in Table 1. All of the alloys of the present invention showed good corrosion resistance, with no occurrence of nozzle corrosion, and the effectiveness of the addition of Ru, Rh, Rd, PL, and Au was confirmed.

(The following is a blank space) (Effects of the Invention) As confirmed by the above examples, the alloy according to the present invention has sufficient nodular corrosion resistance even in an environment where it is in contact with high temperature and high pressure water or steam for a long time. In particular, satisfactory nodular corrosion resistance was obtained even under more severe corrosion conditions than conventional ones, so it can be put to practical use by demonstrating satisfactory corrosion resistance even under more severe conditions such as in the primary water of a nuclear reactor. , and its practical benefits are large.

Claims (3)

[Claims] (1) Sn: 0.20-1.70%, Fe: 0.05-0.5 in weight%
0%, Cr: 0.05-0.30%, one or more selected from the group consisting of Ru, Rh, Pd, Pt, and Au, total 0.005-3.0
A nodular corrosion-resistant zirconium alloy consisting of 0% Zr and the balance Zr and inevitable impurities. (2) The nodular corrosion-resistant zirconium alloy according to claim 1, further containing 0.01 to 0.10% Ni. (3) The nodular corrosion-resistant zirconium alloy according to claim 1 or 2, further containing Nb: 0.05 to 1.50%.