Patent Number: 048805599
Section: description

EXAMPLE 1 Samples of tubes from the steam generator of a pressurized water nuclear reactor about 1% inches long and 3/4 inches in diameter were cut in half longitudinally. The samples were placed in beakers containing various decontamination solutions (except in some experiments the solutions were circulated over the samples in the beakers). After each sample was treated with a decontamination solution, the decontamination factor was determined. (The decontamination factor (DF) is the radioactivity in microcuries before treatment divided by the radioactivity in microcuries after treatment.) The following table gives the sequence of treatment of eleven different samples treated with various decontamination solutions for different times and temperatures. In the table, "CM" is a commercial decontaminating solution believed to be 30% citric acid, 30% oxalic acid, 40% ethylenediaminetetraacetic acid, and containing an inhibitor believed to be thiourea. "CAS" is ceric ammonium sulphate, "CAN" is ceric ammonium nitrate, and "TSCA" is tetrasulfato ceric acid. __________________________________________________________________________ Treatment Sequence Step DF Final 1 2 3 4 5 1 2 3 4 5 DF __________________________________________________________________________ .5% CM .1% K.sub.2 FeO.sub.4 4 hrs .5% CM, .5% TSCA, 1% H.sub.2 SO.sub.4 .5% CM 1.06 1.00 1.10 143.06 1.81 300.40 4 hrs, 100C 40C, pH10 4 hrs, 100.degree. C. 6 hrs, 100C 4 hrs, 100C .5% CM .1% K.sub.2 FeO.sub.4, .5% CM .1% CAS, 4 hrs, .5% CM -- -- 1.05 -- 1.00 1.05 24 hrs, 100C 4 hrs, 48C 23 hrs, 95.degree. C. 100C, pH 2.6 10 hrs, 100C " " " .1% CAS, 6 hrs, .5% CM -- -- 1.05 -- 1.00 1.05 100C, pH 2.6 12 hrs, 100C .5% CM .5% CAS, .5% CM 1.10 .94 1.01 1.05 4 hrs, 100C 6 hrs, 100C 4 hrs, 100C " " .5% CM 1.01 1.08 .89 .97 4 hrs, 121.degree. C. " .1% CAS, .1% CAN, .5% CM 1.11 .95 1.34 .88 1.24 6 hrs, 100C .4% HNO.sub.3 4 hrs, 100C 7.5 hrs, 100C " .1% TSCA, .5% C 1.03 1.03 1.03 1.09 .3% H.sub.2 SO.sub.4 4 hrs, 100.degree. C. 7.5 hrs, 100.degree. C. " .25% TSCA .5% C .5% TSCA .5% CM 1.05 1.22 1.03 60.60 .97 77.83 .75% H.sub.2 SO.sub.4 4 hrs, 100.degree. C. 1% H.sub.2 SO.sub.4 4 hrs, 100C 6 hrs, 100C 6 hrs, 100C " .25% CAN, " 1.03 1.02 1.00 1.05 " .75% HNO.sub.3 6 hrs, 100C " .5% CAN, " 1.07 1.11 .94 1.11 1% HNO.sub.3 6 hrs, 100C " .5% CAN, " 1.06 1.13 1.02 1.23 1% HNO.sub.3 6 hrs, 70C __________________________________________________________________________ The above table shows that ceric ammonium nitrate is not effective in decontaminating the samples. It also shows that tetrasulfato ceric acid is very effective at higher concentrations, but is ineffective at concentrations of 0.25% or less. EXAMPLE 2 Example 1 was repeated. The following table gives the results: __________________________________________________________________________ Treatment Sequence Step DF Final Step 1 Step 2 1 2 DF Comments __________________________________________________________________________ 1% H.sub.2 SO.sub.4 .5% CM -- 1.04 1.04 Ineffective 6 hrs, 95C 6 hrs, 95C .5% TSCA, 1% H.sub.2 SO.sub.4 .5% CM 33.81 1.10 37.17 ID still covered 6 hrs, 100C 4 hrs, 100C by oxide layer, effective .5% CAN, " 1.03 1.26 1.29 Ineffective 1% HNO.sub.3, 6 hrs, 100C 5% H.sub.2 SO.sub.4 1.01 1.01 Ineffective 6 hrs, 22C 1% TSCA, 5% H.sub.2 SO.sub.4 1% TSCA, 5% H.sub.2 SO.sub.4 1.01 326.6 329.5 ID still covered 6 hrs, 20C 6 hrs, 100C by oxide no mixing no mixing very effective 5% H.sub.2 SO.sub.4 49.47 49.47 Oxide layer still 6 hrs, 100C present many no mixing cracks __________________________________________________________________________ The above table shows that 1% sulfuric acid by itself was ineffective and 5% sulfuric acid was ineffective at 22.degree. C., but effective at 100.degree. C., albeit with considerable corrosion. (The "100.degree. C." temperature was actually the highest possible temperature that could be obtained without boiling the solution.) The table also shows that the ceric ammonium nitrate-nitric acid solution did not effectively decontaminate the samples. The tetrasulfato ceric acid in combination with sulfuric acid was also ineffective at 20.degree. C., but was extremely successful at 100.degree. C., and much more effective at a concentration of 5 to 6% than was sulfuric acid alone.