Radiation Induced Sodium Metal Colloid Formation in Natural Rock Salt From Different Geological Localities

Abstract

Radiation damage has been studied in natural rock salt from various localities, including potential repository sites. In the 100 to 300 C range the damage consists of point defects, primarily F-centers, and colloidal metal sodium particles. With increasing dose the F-centers grow to a saturation level, reached at IO~~1O S rad, that decreases with increasing temperature to a negligible level at 300 C. Colloid concentration vs. irradiation-time curves follow nucleation and growth curves accurately described by Ct n , or C(dose) n , relations at large irradiation times. For fourteen samples, n*l.85± 0.13 but the values of C vary by a factor of more than 10 3 . The constant C is related to the sample strain, the impurity and void content, dose rate, and possibly other factors. The currently available data indicate that rock salt adjacent to radioactive waste canisters, at a temperature of 150 c, will contain between 0.01 and 10 mole percent of sodium metal when the total dose reaches 10 10 rad.