Patent Number: 050930737
Section: description

EXAMPLE 1 The samples a) of ferritic chromium steel were treated at room temperature (290 K. to 295 K.) for 16 hours with a solution of 0.05 mol each of chromic acid and permanganic acid. After intermediate rinsing, a decontamination factor (ratio of measured activity before and after the treatment) of 2 was found. A further treatment at room temperature in an aqueous 0.1 mol solution of oxalic acid under the action of ultrasonics led to a decontamination factor of about 20 after 15 minutes and to a decontamination factor of more than 100 after 6 hours. After the treatment, the decontaminated surfaces of the samples were metallically bright and not noticeably attacked either macroscopically or microscopically. EXAMPLE 2 Samples c) of nickel/chromium/iron alloys of trade name INCONEL 600 were treated at room temperature for 16 hours with a solution of 0.1 mol of chromic acid and 0.004 mol of potassium permanganate. After intermediate rinsing, a decontamination factor of only 1.2 was found. After a further treatment at room temperature with an aqueous solution of 0.1 mol of oxalic acid for 6 hours under the action of ultrasonics, a decontamination factor of 12 was determined. EXAMPLE 3 Samples a) of ferritic chromium steel, samples b) of austenitic stainless steels and samples c) of INCOLOY 800 and of INCONEL 600 were each treated for 16 hours at room temperature in aqueous solutions with 0.01 to 0.1 mol of chromic acid and 0.001 to 0.05 mol of permanganic acid, the chromic acid/permanganic acid ratio being between 1:10 and 25:1. The samples were then each further treated for 6 hours at room temperature in an aqueous solution of 0.1 mol of oxalic acid under the action of ultrasonics. Finally, decontamination factors of between 10 and 1000 were measured on all the samples, depending on the oxidative treatment and on the sample material. EXAMPLE 4 Samples a) of ferritic chromium steel and samples c) of INCONEL 600 were each treated for 16 hours at room temperature in a solution of 0.1 mol of chromic acid and 0.05 mol of permanganic acid. After a subsequent treatment with a water jet of 2.4 kbar (240 Pa) pressure at a treatment rate of 3.6 m.sup.2 /hour, decontamination factors of about 30 were measured on the samples a) of ferritic chromium steel, and decontamination factors of more than 100 on the samples c) of INCONEL 600. Extensive further investigations showed that the surfaces of the base materials were not attacked by these treatments. EXAMPLE 5 Samples c) of INCONEL 600 were sprayed for 16 hours at room temperature with a solution of 0.05 mol of chromic acid and 0.002 mol of permanganic acid. After a subsequent further treatment with a water jet as in Example 4, decontamination factors of between 20 and 80 were determined. EXAMPLE 6 A paste was prepared from an aqueous solution of 0.4 mol of chromic acid and 0.1 mol of permanganic acid by addition of a thickener which is available on the market under the trade name AEROSIL (registered trademark of Degussa). This paste was spread on the contaminated surfaces of samples a) of ferritic chromium steel. After a period of action of 16 hours, the samples were treated with a water jet as in Example 4. The resulting decontamination factors were between 5 and 15. The tests described by way of example and further extensive investigations showed that the materials normally used in reactor construction for the cooling circuits are not damaged by the treatments using the process according to the invention, irrespective of whether the components decontaminated in this way have aged or have been heat-treated, welded or deformed.