DE2034863C3 - Process for the surface treatment of zirconium and zirconium alloys for fuel elements or other nuclear reactor components - Google Patents

Description

The invention relates to a method for the surface treatment of zirconium and zirconium alloys for fuel assemblies or other nuclear reactor components by pickling in a fluorine-containing bath and subsequent production of an oxide layer

Process for cleaning zirconium surfaces by electrolytic polishing in an electrolyte, which contains about ammonium fluoride and ammonium nitrate, in a subsequent oxidation stage Making corrosion-resistant oxide surfaces are common known (5! E-PS 1 79 120 and DE-PS 11 98 166). After the surface has been cleaned by the Electrolytic polishing uses steam at high pressure and temperature for the oxidation process applied.

The known methods make electrolytic cleaning unavoidable, which leads to one not leads to an insignificant increase in the cost of the process. Also is the possibility of the To make fluoride-containing contaminations sufficiently harmless, what is not given enough is of great importance for use in connection with fuel assemblies for nuclear reactors.

A method is also known by means of which colored oxide coatings on metals of groups IV. V and VI of the periodic table. It is no longer new in this context. that the anodic oxidation of zirconium leads to colored surface coatings (FR-PS 1241646). However, anodic processes, which are only used for decorative purposes, are not more corrosion-resistant for manufacturing Coverings suitable for the purpose of interest here; and the demands placed on them are not comparable.

Rather, the problem at hand comes into play a known method for the decontamination of radioactively contaminated objects and surfaces closer, according to which the contaminated objects of an electrolytic Poiieriing to be subjected. For what they as Anöde "Under complete immersion in one Electrolyte bath are added, or the electrolyte is circulated gradually over the area to be disinfected by means of a movable cathode. (DD-Ps 24 843). Contaminants containing fluids cannot be removed with this procedure alone * bar.

It is known that an oxide coating is used in the zirconium plating of fuel assemblies for nuclear reactors produced, for example, by treating the surface in an autoclave with water or steam at high Temperature of approx. 400 ° C and high pressures of approx. 100 at or by heating in oxygen.

Before this oxidation is carried out, the

The surface can be thoroughly cleaned or stained, for example in a mixture of nitric acid and hydrofluoric acid and water. A suitable bath solution for this pickling process is, for example

HNO ₃ -HF-H ₂ O

in a weight ratio of 41-4-55.

When the surface of the material has been cleaned by this commonly carried out pickling process However, the surface can still be slightly contaminated or contaminated during the subsequent thorough rinsing in water. be contaminated and still be exposed to fluoride compound, which is very disadvantageous affect the corrosion resistance at high temperatures. This fluoride contamination, which as Any residue left on the surface cannot be satisfactory by any of the known methods removed. There is also a lack of usable bath solutions for zirconium and zirconium alloys Pickling process that does not contain any fluorine compounds. When using fluoride containing So far, efforts have been made to reduce the amount of fluoride contamination by the fact that the bath solutions the treated surface was rinsed with water as soon as possible after pickling. To that extent existed a procedural rule is that the rinsing process of the surface of the Maten.i, not more than five seconds

J5 is to be carried out after pickling. In practice this is however, extremely difficult to perform.

The invention is therefore based on the object of developing a method of the type mentioned at the outset in such a way that that it is possible to have a longer time for transmission

-to the pickled objects from the bath solution in one Rinse bath available / u have at the same time the disadvantageous fluoride contamination should be excluded with certainty.

The object is achieved according to the invention by anodic treatment after the pickling is decontaminated and anodically oxidized, both measures in a moving 0.01 to 0.5 molar Alkali, preferably with a content of 0.5 wt.% KOH. at a temperature below 100 "C and the voltage mn not more than IO V per second up to / u a final voltage of at least 30 V increased and the final voltage is maintained until about a constant current flows.

v, F The main advantage of this process consists in the complete removal or rendering harmless of fluoride compounds. which, as the smallest traces, would cause an extraordinary increase in the rate of corrosion of the surface the impurities,

The surface treatment of Zirconium or zirconium alloys ifi connection with the production of fuel elements for nuclear reactors, the ils tubes made of zircon material with nuclear

Fuels can be filled and sealed by welding is due to the two-stage nature of the Method particularly simple and effective, especially as both the anodic decontamination and the anodic oxidation can take place in one and the same bath, but optionally also separately in two Baths.

The electrolyte fluid is moving as the is attached The gas layer otherwise accumulating on the surface of the fuel assembly leads to non-uniform treatment. In addition, the fluoride that is removed from the surface during electrolysis is absorbed by the Movement better distributed.

After the fluoride contamination has been removed from the surface or is harmless are made, the protective oxide layer is applied. There are decontamination and oxidation also executable at the same time.

The anodic oxidation of zirconium is carried out according to the invention in a moving 0.01 to 0.5 molar Alkali hydroxide, preferably and a content of 0.5 % By weight KOH, carried out When using dilute KOH it is possible to make a coating To obtain zirconium, which offers just as good corrosion protection as it does through autoclaving is obtained, provided that the conditions prescribed by the present method be maintained.

An advantage of the invention also lies in the low expenditure of time for the entire process sequence. A Oxide film of 2000 / - as it can be achieved by anodic oxidation, is so insensitive to contamination like a film of 10,000 Å thick in one Autoclave is achievable.

It is also advantageous that the anodic .: decontamination and oxidation through the development of Oxygen at the anode does not allow hydrogen to enter the zirconium-containing material.

There is a further advantage of the anodic decontamination and oxidation used according to the invention in contrast to the processing in an autoclave in that it does not increase the Brings corrosion rate with irradiation or radiation, because the defect structure in the oxide layer in is different in both cases.

Surfaces of a number of zirconium alloys have been treated using the "Zircaloy-2" and "Zircaloy-4" currently on the market. It was found that the alloy composition does not have different effects on the removal of fluoride from the surface.

On the other hand, however, it has been found that the thickness of the applied oxide coatings for different Alloys slightly different The following alloys were treated with positive results:

"Zircaloy-2" with 1.54% Sn. 0.1 3% Fe

0.09% Cr. 0.05% Ni. Rest Zr
»/ Ircaloy-4« with 1.52% Sn. 0.20% Fe.

0.08% Cr. 0.006% Ni. Rest Zr.

2.5% Nb, 0.5% Ta, balance Zn
0.7% V, 0.75% Fe, remainder Zf.
L2% Gu ₁ O ₁ SFe ₁ balance Zr.
0.2% Sn, 0.09% Fe, 0.07% Ni,
0.14% Nb ₁ balance Zr.

The percentages given relate to öewiehisörozente.

Comparative tests with different electrolyte solutions are described in more detail below:

example 1

»Zircaloy ^ i specimens were surface-contaminated with fluoride in the following way: The specimens were placed in a pickling bath solution containing HNO ₃ -HF-H ₂ O in a weight ratio of 41-4-55, the soaking time being 3 Minutes. The temperature of the pickling liquid was 33 ° C. The samples were then removed from the bath solution and kept in air for 20 minutes without the adhering pickling liquid having been removed. During this time, insoluble oxy- and hydroxy-oxide formed on the surface of the samples. The samples were then thoroughly washed and dried

The samples contaminated with fluoride in this way underwent anodic oxidation at different Subjected to electrolyte solutions. Basic as well as neutral and acidic aqueous electrolyte solutions were used here to use. The different electrolyte solutions that have been used are shown in the table 1 summarized As can be seen from this table, the examined electrolytes contain 0.5 to 3 wt .-% a salt, an acid or a base. During all tests, the temperature of the electrolyte solution was held at 20 ° C.

Anodization was carried out in the same way in all of the electrolyte solutions. The samples were for this purpose connected to the anode of a direct current source, whereby the connecting material made of »Zircaloy-2« duration. The cathode was made of platinum. To carry out the electrolysis, the current was switched on and

the voltage increases from 0 to 125 V at a rate of 5 V / per second. Once the final tension was achieved. this was kept constant over a period of 1 minute, the current flow in this Time was almost constant. The specimens were then removed, washed in water and dried. Subsequently, these test pieces were subjected to corrosion processing together with reference samples subjected to superheated steam for a period of 4 days, the temperature of the steam

was 400 "C and (the pressure applied was 50 kp / cm ^2. The appearance of the test pieces after the anodizing or electrolysis treatment and the corrosion test, as well as the weight increase, is summarized in Table 1 and can be taken from this.

men.

According to the American Society for Testing Materials. Specification J5J-64T for zirconium alloys. "Zircaloy-2" and "Zircaloy-4". The corrosion test was carried out in a steam stream at 400 "C.

Ϊ5 After the material has been subjected to this test was. it should have an even, shiny black oxide layer, free of white and brown corrosion own products The weight gain should be less than 22 mg / dnv. F. according to this specification

were the fluoride contaminated, do not anodize Corrosion test specimens unsatisfactory, as well as some of the anodized ones Specimens,

As can be seen from the table mentioned, was a satisfactory appearance in connection with the slightest signs of corrosion only when used the following alkali liquor is achieved as an electrolyte, which all have a sufficient concentration of

Contained OH ions, Zq these alkaline solutions are also counted as NH ₄ OH.

0.5% NH ₄ OH
0.5% LiOH
0.5% NaOH
0.5% KOH

Stronger corrosion effects were _{found during anodization in NaNO 2} , while LiNO ₃ and ICNO ₃ oxide layers or films without a satisfactory one

10 gave appearances which, however, produced relatively small weight gains on exposure to superheated steam.

Borate or boric acid electrolytes seem to be of little advantage in this context, while sulfates, sulfites, carbonates and phosphates, for example, also turned out to be unsuitable for removing fluoride contamination. In this context it should be mentioned that the solubility of the fluoride ions in solutions of Ba ⁺⁺ and Ca ⁺ + is very low at low temperatures

Table 1 pH Look after the Total weight Look after the Electrolyte specification in% by weight Anodizing increase n.d. Autoclave test Autoclave test in mg / dm ² 7th gray-white 16.6 greyish. dull LiNO, 1% 13th appealing 17.9 claim black NH ₄ OH 0.5% 13th appealing 17.9 claim black LiOH 0.5% 7th gray-white 18.4 grayish, dull KNOj 1% 13th Ansp: green 18.8 claim black NaOH 0.5% 13th claim green 19.0 claim black KOH 0.5% 8th claim red-pink 22.1 claim black NaNO ₂ 1% 6th claim light green 24.9 some white spots NH ₄ tartrate 3% 10 claim red-pink 25.4 claim black NaB ₄ O ₇ 1% 1 claim light green 26.4 claim black citric acid 1 claim light green 27.5 some white spots Tartaric acid 10 claim green 29.7 some white spots K ₂ CO ₃ 1% 13th claim green 31.6 appealing Ca (OH) ₂ 1 claim green 31.8 appealing Ba (OH) ₂ 7th claim Red Green 33.7 white flecki Na ₂ HPO ₄ 1% 9 claim Red Green 44.0 gray-white Na ₃ PO _4. % 8th claim light-g, ün 46.5 White K ₂ SO ₃ 1% 7th claim light green 49.2 White K ₂ SO ₄ 1% 1 claim light green 52.2 White H ₃ SO ₄ 1% 7th claim light green 53.3 White Na ₂ SO ₄ 1% 20.0 black Not anodized immediately after normal stain washed resp. rinsed off 42.1 White Not anodized, fluoride contaminated

Regarding the weight gain and appearance of the anodized fluoride-contaminated specimens: The weight gain is as total weight gain after anodizing and autoclave treatment and represents the mean value of two parallel tests.

It can be seen from this table that only the 0.5% alkaline solutions in the subsequent corrosion = test produces satisfactory results

Example 2

The surface of "Zircaloy * 2" 'specimens is treated with fluoride as described above. The temperature of the pickling bath was 35 ° C, and the same The dwell time in air was 20 minutes. The specimens were washed particularly thoroughly in this line, s .; that all of the fluoride that was not chemically bonded to the surface has been removed.

The samples were then anodized in a basic electrolyte solution (0.5% KOH) in the same manner as reported above. The reference coupons were not anodized. The electrolyte used, namely a fresh solution, was checked for the fluoride content. In the electrolyte solution, 2.0 ■ ΙΟ- ⁵ MoI F- were found, whereas the fluoride concentration in the fresh solution was below the detection limit of the analysis method, which was 3, 5 · 10 ^-6 moles of F-. The proven fluoride content corresponds to the removal of 14 μg F per cm ^{2 of} the surface.

All specimens were subjected to a corrosion treatment in ^{hot steam of 40O 0} C, and it

it was found that the anodized samples had a uniform black oxide layer, while the non-anodized specimens were spotty white.

In order to investigate the relationship between the amount of fluoride on the surface of the zirconium alloys and the degree of white oxide that forms at SlandardkoriO-sionstesls (400 ⁰ C steam), the following experiments were carried out:

"On the surface of" Zircaloy-2 "drops of a water-soluble compound of HF were distributed over 1 cm ^{2 of} surface area. The drops had a volume of 0.05 ml and a fluoride content that produced a fluoride contamination of 0.5 to 200 μg / cm ² on the surface.

A number of test pieces were subjected to a treatment in an autoclave with steam of 400 ^° C. and a pressure of 50 kp / cm ² for two days. It was found that traces of white or colorless oxide (the rejection limit according to ASTM Specification 353-64T) were approx. 5 μg / cm ² , in accordance with Rynasiewiez (USA EC Report KAPL-20CKM9, Reactor Technology, Report No. 22 - Chemistry, J.- Ry η asiew ie ζ, 1962), which reports that 8.5 to 17 μg F / cm ² are required for an approximately uniform white oxide layer.

It was also found that, with a corresponding comparison, the stability test method, which was carried out using appropriately prepared, fluoride-contaminated surfaces in Example I, led to an areal density of 10 to 20 μg F / cm ² .

If you compare these muscles to the amount of fluoride found in the electrolyte has been, the conclusion can be drawn that the fluoride from the surface during the anodization is removed and that the amount removed is of the same order of magnitude as that Total amount of fluoride that the white oxide was on the non-anodized surface of the tensile specimens brought forth.

example

To determine the voltage required to remove all of the fluoride from a test piece in which the pickling solution had been dried from the surface, the following tests were carried out: The pickling liquid used was the same as described in Example 1, and the test pieces were applied fluoride contaminated in the same way. The amount of fluoride on the surfaces of the samples was accordingly approx. 10 to 20 μg F / cm ² before anodization.

The anodizing solution consisted of 0.5% KOH and the test material was "Zircaloy-4". Samples were anodized so that the voltage for all samples was increased at the same rate, with the final voltage has been varied between 6.4 and 100 V. is after reaching the desired final voltage

WUiOc üicäc iuf £ Wci iviifiuicfi i \ oit5tdfti gcfiimcfi, Ocvur

the power was switched off again. The test pieces were then subjected to a treatment in an autoclave, specifically at a steam of 400 ^° C. and 50 kp / cm ² pressure over a period of three days.

The anodizing stresses, the weight gain during anodizing and treatment in the Autoclaves and their appearance after treatment in the autoclave are summarized in Table 2.

After the samples were autoclaved, they showed a noticeable difference in their appearance. The samples that undergo anodization or electrolysis at 30 V and below all showed a similar appearance and were uniformly gray-white while all specimens where the voltage during electrolysis was 50 V and above, a black one, showed a bright shiny appearance. There was no uniform transition from the grayish to the black appearance, but a very noticeable difference between those at 30 and those at 50 volts Treated samples. At the total weight of the weight it can be seen that those specimens which were anodized at 30 volts and below did not are acceptable, while the specimens whose anodizing voltage was 50 V and above failed quite move in the ASTM regulations.

Table 2

Appearance and weight gain after autoclaving of fluoride contaminantsi "Zircaiöy-4" test pieces after anodizing at various Tensions

Final voltage in volts

6.4

8th
10
15th
20th

Weight increase in μ% / άτη ²

during the during the total anodizing treatment

in the autoclave

0.2
0.3
0.5
0.8
1.0

34.3
33.3
32.3
29.8
29.8

34.5
33.6
32.8
30.6
30.8

Look after
the treatment
in the autoclave

gray-white
gray-white
gray-white
gray-white
gray-white

continuation Weight gain in g / dm ²
during the during the
Anodizing treatment
in the autoclave 23.1 total Look after
the treatment
in the autoclave Final voltage in volts 1.6 18.0 24.7 gray-white 30th 2.7 16.8 20.7 black 50 4.2 13.1 21.0 black 75 5.7 10.7 18.8 black 100 7th - * 17.7 black Not with fluoride
contaminated
125 - - ».. ... ~.: N
gf QU-ITViIU i'iüumu KGHui ΐΤΐί HiCTl
not anodized

example

Samples of "Zircaloy-2" were fluoride-contaminated by drops, as described in Example 2. The concentration on the surface was 10 μg F / cm ² .

A series of test pieces was dissolved in 0.5% NaOH at different final voltages (30,50, 70 urd90V) anodized, namely at 0 ⁰ C, while another series were anodized specimens in the same electrolyte at the same voltages at 100 ° C .

The anodized at equal voltages Probestükke showed different interference colors at ^{0 °} C and 100 ° C, which indicated that at 100 ⁰ C, a thicker oxide layer is formed as at 0 ° C.

After the test in the autoclave (3 days at a steam of 400 ^° C. and a pressure of 5G kg / cm ² ), no significant differences could be found in the two test series with regard to the removal of fluoride. The samples anodized at the three highest voltages were black and completely similar. The anodization at low voltages the samples whose Anodisierungstempefatur was 100 ⁰ C were somewhat better than those that have been anodized at 0 ⁰ C, failed. Accordingly, the temperature of the anodizing bath should have so little influence on the removal of the fluoride that any temperature at which the electrolyte is liquid can be used. In practice it is advantageous to work at room temperature.

example

"Zicaloy-4" specimens were surface treated as described in Example 1. The duration of these test pieces in air before the subsequent washing process was between 5 and 15 minutes. Reference specimens were washed off immediately after pickling. Some of the test pieces were anodized in a basic electrolyte. The anodizing process or the electrolysis was carried out in the same way as previously described. The electrolyte contained an aqueous solution of KOH (0.5%) and a final voltage of 125 V was used. All test pieces were then tested in water and steam at 230 ^° C. The results obtained are summarized in Table 3

From this table it can be seen that an increased level of fluoride contamination increases the corrosion rate for non-anodized specimens are enlarged with a significantly higher corrosion rate than for an anodized one Sample is. The oxide on the test pieces was gray-white and blotchy. All anodized specimens showed the same low weight gain during autoclave treatment, independently the degree of original fluoride contamination.

Those samples which have the shortest length of stay in air (5 minutes) were given a complete after anodization uniform red-green color coating and were uniformly black after autoclaving with a shade or tint of red-green. The samples that have been kept in the air for longer were (30 minutes) with a higher fluoride contamination were after anodizing blotchy and showed areas of pure green and other areas of pure red. The spotty one The surface was also visible in the black oxide layer, although this was not shaded white or gray which can be attributed to abnormal oxide formation.

If the fluoride contamination exceeds a certain limit then it can through the Anodization can be directly demonstrated that the object is fluoride-contaminated The weight gain during the subsequent corrosion treatment showed that the originally different fluoride-contaminated specimens exhibited the same corrosion rate after anodization. When a If fluoride residue was present on the test pieces, this amount was the same on the test pieces after the anodization zv / ei rows of specimens, and this amount was almost as little or less than on a specimen, which was subjected to a washing process immediately after the pickling process.

Table 3

Weight gain of »Zirdaloy-2« during the corrosion test in water + steam under

increased pressure and 230 ^r C

AufenlhHts- anodization atmosphere Weight increase duration in air in the autoclave in mg / dm ²

after (Lm heating process

10 days 30 days appearance

2 see. no water 5.5 6.6 black 5 min. Yes steam 7 *) 7+ 0.1 black 5 min. Yes water 7 *) 7+ 0.1 black 30 min. Yes steam 7 *) 7+ 0.1 black, blotchy 30 min. Yes water 7 *) 7+ 0.1 black, blotchy 5 min. no steam 5.8 7.8 horny gray-white 5 min no water 5.2 10.4 mottled gray-white 30 min. no steam 7.1 11.7 mottled gray-white 30 min. no water 9.5 21.4 mottled gray-white

*) The anodized test pieces show no weight gain during the first test period. The weight gain of 7 mg / dm ² was obtained during the anodization.

Example 6

The determination of the detection limit for fluoride was carried out in such a way that test pieces were contaminated with fluoride, namely with fluoride amounts of 0.5; 10; 25; 50; 100; 200 mg / cm ² using the same technique as described in Example 2. The specimens were then anodized in NaOH at a pH of 14 and a final voltage of 125 V and then treated in an autoclave with steam at 400 ⁰ C and at a pressure of 50 kgf / cm ^2. Corresponding reference specimens were treated directly in the autoclave without prior anodization. A contamination of about 5 μg F / cm ² and higher results in the color shades of ηπϋνιί5ΐ6ΓϋΓΪ £ icStgcStciit were found. lmC exact

45

50

55

60

Detection limit could not be determined; however, it is probably lower than it is for the ones shown here Traces of fluoride could be of concern.

After treatment in the autoclave, the non-anodized samples with a contamination of 5 μg F / cm ^{2 were} slightly gray, while the samples with 0.5 μg F / cm ² that had been anodized showed a uniform black color.

It was also found that the fluoride contamination can be removed from the surface with concentrations of up to 50 μg F / cm ² . At higher concentrations, the specimens cannot be subjected to anodization, by means of which the fluoride contamination is present as an upper residue on the surface, which showed rapid corrosion during the autoclaving. However, the limit is higher than the contamination that is present if the surface has been dried off immediately after pickling.

Example 7

In order to check further oxidation processes, soft to remove the fluoride contamination Oxygen was used. The specimens were under for 24 hours at 350 ° C Influence of oxygen oxidized Here, the test pieces received an oxide layer, which was the same Thickness was as it was obtained in the anodic oxidation of the samples in Example 1, namely approx. 5000 A.

The test pieces thus treated were subjected to the corrosion test at 400 ° C. The corrosion test showed that the heat oxidation had no effect on the corrosive effect of the specimens, since these specimens have a higher weight gain than the untreated fluoride-contaminated samples and the surface of the samples was white and stained. The thermal oxidation can, however, the anodization for the removal of the fluoride contamination do not replace.

Example 8

In this exemplary embodiment, three rows of tube-like test pieces of "Zircaloy-2" were pretreated in the pickling bath already described above. After pickling, the specimens were kept in the air for different time intervals (1 second to 10 min) before they were thoroughly washed and then dried. A number of the specimens were subjected to anodic oxidation. The electrolyte used for this was basic (0.5% KOH), and the final voltage used in the electrolysis was 125 V. The festive two rows of test pieces were heated by superheated steam at 400 ° C and a pressure of 100 kp / cm ² or 25 kp / cm ² oxidized over a period of 3 days. All samples were subsequently subjected to a corrosion test in a steam atmosphere of 400 ⁰ C for 30 days. According to this, the non-anodized samples showed a white speckled appearance and a high increase in weight, while the anodized sample pieces were uniformly coated in black with an oxide layer and had a very low corrosion rate. This result shows that the fluoride contaminants had been removed or at least rendered harmless before the specimens were exposed to the steam. The anodized test pieces also showed

a longer test period (550 days) an even low corrosion rate, while the autoclaved specimens at increased speed corroded.

Example 9

To a 0.5% NaOH solution, fluoride was added in the following amounts: 4, 8, 21, 42, 210 and 420 ppm. The specimens were anodized in the solutions and post-treated in the autoclave. Here it was found that the anodization process or the electrolysis process in solutions which up to Contained 210 ppm F was normal, while one Content of 420 ppm F in the anodizing solution, the erosion was influenced and an oxide layer which formed a high rate of corrosion during the subsequent autoclave treatment process produced.

From this it can be concluded that for fluoride contamination

Mination of the order of 10 to 20 μg F / cm ² per liter of electrolyte, the anodization can be carried out without any disturbances and the fluoride contamination is absorbed by the solution.

Example 10

To provide further clarification for the procedure, an example of editing a given fluoride-contaminated object, the object initially at a certain Voltage is anodized to remove the fluoride bound on the surface, d. H. so one Is subjected to electrolysis, and the object then continues on a higher voltage is anodized to thereby create a protective coating against corrosion and various mechanical Get influences.

For this purpose, a pipe made of »Zircaloy-2«, welded at both ends, is used in the example used.

This tube is placed in a pickling bath solution. which HF-HNOj-H2O in a weight ratio from 4-41-55 contains. The temperature of the pickling bath was 34 ° C. and the pickling time was 3 minutes. After this For pickling, the tube was kept in the air for 10 minutes, during which the liquid dried up. Afterward the tube was washed thoroughly and dried. A bath solution was used for anodizing used, in which 5 g of NaOH per liter had been introduced. The temperature of the bath was 19'C.

and the liquid was kept in constant motion with a motorized stirrer.

The length of the tube was 60 cm and the effective surface 290 cm ² . The cathode was made of platinum, namely a wire of 2 mm 0, which in the

f5 was located close to the anode over the entire length and had an effective surface area of 36 cm ² .

The electrodes were connected to a DC power source and the voltage applied at a rate

elevated. This tension was held constant for 2 minutes. The anode then showed a red-purple Appearance with light pink spots indicating that the anode was fluoride contaminated.

The voltage was then slowly increased from 60V to 125V at a rate of 2V per second. This final voltage was kept constant over a period of 2 minutes, the direct current having a flux density of about 0.3 A / dm ² . The power was then turned off and the item removed from the bath to be washed in cold water.

The thickness of the oxide layer obtained in this way could be increased according to this method, and from 2000 Ä to 4400 Ä. An article treated in this way had a better oxide layer in this respect covered so that it was insensitive to any interference, and at the same time it was a Oxidation process initiated, which ensured a normal, low rate of corrosion when the object exposed to high temperature in water and steam.

Claims (1)

20th OCQ OU.J Claim: Process for the surface treatment of zirconium and zirconium alloys for fuel assemblies or other nuclear reactor components by pickling in a fluorine-containing bath and then Production of an oxide layer, characterized in that after pickling, anodic is decontaminated and anodically oxidized, both measures in a moving 0.01 to 0.5 molar alkali, preferably with a content of 0.5 wt .-% KOH, at a temperature below 100 ° C and the voltage with no more than 10 V per second up increased to a final voltage of at least 30 V and maintained the final voltage for so long until about a constant current flows