Abstract: STUDY ON THE LEACH MECHANISM OF 90-19/U GLASS FORM IN UNDER GROUND WATER OF DISPOSAL SITESheng Jiawei ;Luo Shanggeng;Tang Baolong (China Institute of Atomic Energy , P. O. Box 275 ( 93 ),Beijing 102413 )Abstract:The leach behavior of 90-19/U glass form in underground water (UW) of disposal site and in the deionized water (DIW) is studied. The total mass losses of glass form and the normalized element mass losses of B, Li and Si in UW are presented and compared to DIW.It is found that the ions in UW affect the leach behavior of 90-19/U glass.At the beginning of the reaction the reaction rate of the glass is smaller in UW than in DIW due to the low glass dissolution affinity in UW which is defined as (1-c/K).The rate determining step of leach reaction of 90-19/U glass in UW during the entire reaction period is the ion-exchange reaction. The apparent activation energy of glass reaction in UW is 51. 6kJ/mol.Keywords: Glass form Underground water Ion-exchange reaction Apparent activa tion energy