Experimental evaluation of removal factor in smear method for surveying radioactive surface contamination of transport cask

The removal factor in the smear method was measured experimentally for materials that are used in transport casks for spent fuel, storage casks and ships for transporting them. We used 60Co for fabricating contaminated tested materials, because 60Co is the key radioactive nuclide contaminant at nuclear power stations. For the tested metallic materials, the removal factors obtained experimentally ranged from 0.7 to 0.8. The removal factors obtained experimentally were 0.4 for the surface of a transport stand and hatch, 0.5 for the surface of the upper deck and 0.3 for the surface of the storage cask. These values can be used to survey radioactive surface contamination. The removal factor was measured with varying pH of a radioactive standardized solution. The removal factor of SUS304 buff polishing (no.300) did not change even when the pH of the radioactive standardized solution was changed. For painted materials, there was the tendency that the higher the pH of the radioactive standardized solution, the smaller the removal factor. However, at a pH greater than 3, the removal factor reached a saturation point. It is concluded that pH of the radioactive standardized solution is ineffective for determining the removal factor when the pH exceeds 3. The removal factor was also measured with varying direction of wiping the surface of the tested materials treated by mechanical cutting. No differences among the cases of the various directions of wiping the surface of the tested materials were observed. (author)