Patent Number: 050733338
Section: description

The invention will now be further illustrated by the following working examples. EXAMPLE Four experiments were performed on test materials taken from Ringhals 2 PWR (=pressure water reactor), where in all experiments two samples from "manway insert" and two tube samples from steam generators were utilized. The characteristics of each of said four experiments are presented below: EXPERIMENT 1: Chemistry: (dissolved in H.sub.2 O to 1000 ml) PA1 22 ml of HClO.sub.4 :0.25M PA1 O.sub.3 :5-15 ppm (in solution ) PA1 t=22.degree. C. PA1 Stirring PA1 Exposure time: 18 h PA1 Chemistry: (dissolved in H.sub.2 O to 1000 ml) PA1 22 ml of HClO.sub.4 :0.25M PA1 8 g of cerium nitrate with all cerium as Ce.sup.4+ PA1 O.sub.3 : no addition PA1 t=22.degree. C. PA1 Stirring PA1 Exposure time: 18 h PA1 Chemistry: (dissolved in H.sub.2 O to 1000 ml) PA1 22 ml of HClO.sub.4 :0.25M PA1 50 mg of Cr.sup.6+ as CrO.sub.3 PA1 O.sub.3 : no addition PA1 t=22.degree. C. PA1 Stirring PA1 Exposure time: 18 h PA1 Chemistry: (dissolved in H.sub.2 O to 1000 ml) PA1 8 g of Ce(No.sub.3).sub.3 .times.6 H.sub.2 O PA1 22 ml of HClO.sub.4 :0.25M PA1 50 mg of Cr.sup.6+ as CrO.sub.3 PA1 O.sub.3 :5-15 ppm (in solution) PA1 t=22.degree. C. PA1 pH=0.76 PA1 Stirring PA1 Exposure time: 18 h PA1 Chemistry: (dissolved in H.sub.2 O to 1000 ml) PA1 8 g of Ce(NO.sub.3).sub.3 .times.6 H.sub.2 O PA1 17.5 ml of HNO.sub.3 : 0.25M PA1 O.sub.3 : 5-15 ppm (in solution) PA1 t=22.degree. C. PA1 Stirring EXPERIMENT 2: EXPERIMENT 3: EXPERIMENT 4: Gamma-spectrometric measurements (only Co60) of the samples before and after the decontaminations gave the following decontamination factors: ______________________________________ Measured Decon factors ______________________________________ Experiment 1: Insert sample 1 1.03 Insert sample 2 .apprxeq.1 Steam generator tube sample 1 1.08 Steam generator tube sample 2 1.1 Experiment 2: Insert sample 1 178 Insert sample 2 165 Steam generator tube sample 1 3.6 Steam generator tube sample 2 5.35 Experiment 3: Insert sample 1 .apprxeq.1 Insert sample 2 1.03 Steam generator tube sample 1 1.05 Steam generator tube sample 2 1.05 Experiment 4: Insert sample 1 5850 Insert sample 2 6400 Steam generator tube sample 1 66700 Steam generator tube sample 2 17700 ______________________________________ Based on the Decon factors obtained it is clear and unambiguous that the combination of all oxidation agents in accordance with the present invention (experiment 4) gives a synergistic effect which was not predictable in view of the known properties of the oxidation agents per se. Furthermore, a comparative experiment was performed in the manner described above and in accordance with those characteristics which are presented below for experiment 5. Said experiment 5 corresponds to the method according to the above-mentioned Swedish patent specification 8401336-6. EXPERIMENT 5: ______________________________________ Mesasured Decon factors ______________________________________ Insert sample 1 3870 Insert sample 2 2980 Steam generator tube sample 1 1830 Steam generator tube sample 2 1880 ______________________________________ A comparison between the result of the above-mentioned experiment 4 and that of experiment 5 shows that the decontamination according to the present invention is quite superior to the decontamination obtained by the previously known technique.