Zinc dosing for decontaminating light-water reactors

Abstract

The invention relates to a method for decontaminating a radioactively contaminated metal surface, wherein the metal surface is brought in contact with a decontamination solution, which comprises a complexing agent and a transition metal. The invention further relates to such a decontamination solution and to the use thereof to decontaminate a metal surface.

Claims

1. A method for decontaminating a radioactively contaminated metal surface, comprising the steps of: bringing at least a portion of the metal surface into contact with a decontamination solution comprising a complexing agent selected from hydrofluoric acid, phosphoric acid, nitric acid, methane sulfonic acid and carboxylic acids, such as nitrilotriacetic acid, ethylenediaminetetraacetic acid, oxalic acid, tartaric acid, citric acid and picolinic acid and salts thereof, and an ion of a transition metal.

2. The method according to claim 1, wherein the ion of the transition metal is selected from the group consisting of zinc, nickel, cobalt or mixtures thereof.

3. The method according to claim 1, wherein the concentration of the transition metal lies in the range of from ≥0.5 to ≤15 mg/kg.

4. The method according to claim 1, wherein the ion of the transition metal is zinc and is present in a concentration in the range of from ≥2 to ≤5 mg/kg.

5. The method according to claim 1, wherein .sup.58Co and/or .sup.60CO ions are removed from the metal surface.

6. The method according to claim 1, wherein the decontamination solution is introduced into the primary circuit of a nuclear reactor.

7. The method according to claim 1, wherein the decontamination solution is circulated.

8. The method according to claim 1, wherein, as the first method step, the method comprises a pre-oxidation step or a reduction step for oxidizing or reducing the radioactively contaminated metal surface.

9. The method according to claim 1, wherein the method also comprises the step of: removing at least some of the radioactive isotopes present in the decontamination solution.

10. The method according to claim 9, wherein all the method steps are repeated at least once.

Description

EXAMPLES

(1) The figures show in detail:

(2) FIG. 1 the correlation between the Zn concentration of the decontamination solution and the 60Co decontamination.

(3) FIG. 2 the correlation between the Zn concentration of the decontamination solution and the 60Co decontamination.

(4) FIG. 3 the correlation between the Fe concentration of the decontamination solution and the 60Co decontamination.

EXAMPLE 1: CORRELATION BETWEEN THE ZN CONCENTRATION AND THE .SUP.60.CO DECONTAMINATION

(5) Decontaminations of the primary circuit of a light-water reactor were carried out, whereby the average Zn and Fe concentration in the decontamination medium and the .sup.60Co removed from the decontamination solution in this case by means of the ion-exchange resin (strongly acidic cation-exchange) was determined. The primary circuit decontaminations were carried out over 15 cycles.

(6) As can be seen in FIGS. 1 and 2 (determination of the .sup.60Co decontamination on the basis of the Zn concentration), there is a very good correlation between this transition metal and the amount of .sup.60Co removed.

(7) In comparison thereto, it was not possible to demonstrate a very good correlation of this type between the Fe concentration and .sup.60Co (see FIG. 3).

EXAMPLE 2: CORRELATION BETWEEN THE NI CONCENTRATION OR CR CONCENTRATION AND THE .SUP.60.CO DECONTAMINATION

(8) Example 1 was repeated, whereby the Ni concentration or the Cr concentration was observed instead of the Zn concentration. In this case, a correlation was likewise shown between the concentration of the transition metal and the activity removed by means of .sup.60Co in each case. The correlation determined decreased tendentially, and in comparison with Zn, from Ni by means of Cr.