The contemporary materials cycle for radioactive 137Cs in the United States

The materials cycle for (137)Cs, a low-level radioactive material of interest from a security perspective (as a possible source for "dirty bombs") as well as for its extensive industrial and medical uses, has been characterized for the United States for the year 2000. The focus is on products utilizing the isotope rather than on isotope production and subsequent disposal as a result of nuclear power generation. The results indicate that, during 2000, of the 1.5 PBq of (137)Cs that entered use, 94% was contained in sources in imported devices; the amounts in domestic source material recycling (4%) or as imported source materials (2%) were trivial by comparison. Losses from use were about 0.5 PBq; of this amount 86% was by radioactive decay, 11% was active source material that was recovered and recycled, and 3% was source material sent to low-level disposal sites. The current stock of (137)Cs in use is about 20 PBq; this stock is currently growing by more than 1 PBq per year (the difference between inputs to and losses from use). As a result, the security challenge related to monitoring stock in use is increasing by around 5% per year.