Assessment of Cs-137, Am-241, and Cf-252 in Well Logging

This paper assesses radiation exposures resulting from 137Cs, 241Am, and 252Cf during well logging incidents. Based on a hypothetical rupture incident, the computer code RESRAD-OFFSITE is run for both offsite and onsite exposure locations. The absorbed doses are compared among three radioactive sources. The adverse health and environmental impact of 241Am is higher than the impact from the other two radioactive sources (137Cs and 252Cf) due to its relatively long half-life and radioactive progeny. The serious impact of 241Am will appear many years after its abandonment depending on its initial activity in the soil. For offsite, the highest maximum dose is due to 241Am (6.18 mSv y-1), which is more than 22 times the maximum doses from 137Cs and 252Cf. For onsite, the highest maximum doses are due to 241Am (121 mSv y-1), which is more than twice the maximum doses from 137Cs and 252Cf. For offsite and onsite, the dominant pathway for 137Cs is direct radiation from soil, the dominant pathway for 241Am is drinking water followed by plant ingestion, and the dominant pathway for 252Cf is direct radiation from soil. Doses from 137Cs and 252Cf are mainly impacted by the contamination on the surface. For 241Am, the opposite is true. Americium-241 doses are mainly impacted by the contamination below the surface. Based on these findings, the exposure impact for replacing an 241Am neutron source for well logging with 252Cf is assessed.