Radon Measurements at the Molten Salt Reactor Experiment (MSRE) Facility from August 1997 through April 1998

Planned remediation at the Oak Ridge National Laboratory (ORNL) Molten Salt Reactor Experiment (MSRE) facility created the need to measure 220Rn and its progeny in air within work areas. Most of the original 233U fuel material is still present in the process system at the facility and will eventually be removed as decommissioning progresses. A hazard associated with the 233U material is the production of 220Rn from the 232U decay chain. Although 232U is in 233U material at a small mass fraction, it can equate to a significant activity level due to its short half-life. To illustrate the magnitudes of activity expected, consider the fuel material in the MSRE facility, which contains 232U at a mass concentration of 160 ppm. After a period of about 13 years, the 228Th activity would have equilibrated to about 3.5 Ci/kg of uranium. A kilogram of uranium would therefore be expected to produce 220Rn at a rate of 1.3E11 atoms/s, or 4.4E-2 Ci/s