Containment of 220Rn via adsorption on molecular sieves for HTGR--OGCS

Radon-220 emission presents a potential problem in the reprocessing of nuclear fuels containing 232U or 232Th. We have examined a number of molecular sieve substrates capable of delaying this short-lived, gaseous radioisotope and have found that a synthetic hydrogen mordenite is most suitable in attaining decontamination factors (DF's) greater than 102 in a carbon dioxide atmosphere. Low concentrations of NO2, SO2, I2, Kr, Xe, and NH4CO2NH2 have little detectable effect. Moisture, however, causes progressive decrease in the ability of the molecular sieve to delay 220Rn. This effect is temporary; regeneration of the bed removes water and restores its ability to delay 220Rn. In laboratory scale experiments, an average DF of 1.5 x 103 was attained with a 3.05-m bed at 12.8 m/min. No evidence was found to indicate that significant transport of 220Rn daughters from the molecular sieve occurs