IAEA SRS No. 44の評価手法に準拠したU-234, U-235及びU-238のクリアランスレベルの解析

抄録

In IAEA SRS No. 44, clearance levels for radionuclides of natural origin (e. g. U-235 and U-238) are judged to be 1 Bq/g from consideration of the upper end of the worldwide distribution of activity concentration in soil. However, a result of estimating the radiological effect of the clearance level is not shown. In this paper, in order to confirm the radiological effect of the clearance level (1 Bq/g) based on the activity concentration in ubiquitous unmodified soil, we estimate the clearance levels for major radionuclides of U-234, U-235 and U-238 in the solid materials contaminated with uranium on the basis of dose calculation approach for radionuclides of artificial origin in IAEA SRS No. 44, which are generated from the processes of nuclear fuel cycle facilities such as conversion, enrichment and fuel manufacturing. The activity concentrations of U-234, U-235 and U-238 are calculated to be 1.2 Bq/g, 0.53 Bq/g and 1.1 Bq/g respectively for applying effective dose criteria and a skin equivalent dose limit. It is confirmed that the activity concentrations estimated using the dose calculation approach are consistent with the clearance levels of IAEA derived on the basis of the worldwide distribution of activity concentration in soil.