USE OF CO-60 GAMMA-IRRADIATION TO SIMULATE DECOMPOSITION OF TETRAPHENYLBORATE PRECIPITATES FROM HIGH-LEVEL RADIOACTIVE-WASTE

The Co-60 gamma radiolysis of potassium tetraphenylborate (KTPB) precipitate was studied at 25-degrees-C in the presence of added Na+, NO3-, NO2-, and OH- ions, and after washing to remove the added ions. Analyses were done on the aqueous layer and after dissolving the solid in acetonitrile to release trapped products into solution. In the case of unwashed 8 wt% KTPB slurries, the products and their initial G-values are as follows: benzene, 6.7 (from dissolved solid); biphenyl, 1.6 (from solution) plus 0.44 (from dissolved solid); and nitrobenzene, 0.040 (from solution). Long term irradiation experiments (up to 60 days at a dose rate of ca. 0.32 Mrad/h) were carried out on unwashed and washed KTPB slurries; experiments were also done on washed precipitates at a threefold lower dose rate. Again, benzene, biphenyl, and nitrobenzene were found along with trace amounts of o-, m- and p-terphenyl. Individual product yields were higher at the lower dose rate, but the measured yield for destruction of KTPB was nearly dose-rate independent. Average yields over 10-40 days were ca. 0.2 to 1.0 for benzene (from the crystals), 0.04 to 0.4 for biphenyl (significant yields found from both solid and solution), and 0.001 to 0.03 for nitrobenzene (entirely from solution). However, under certain conditions, several of the individual yields approached plateau values or even peaked and decreased as irradiation continued.