AGING OF A BITUMEN WASTE FORM IN WET REPOSITORY CONDITIONS

摘要

SIA 'Radon' has been performing field tests of bitumen waste forms holding low and intermediate level wastes (LILW) for about three decades. The waste forms were made at an industrial bituminization plant from the actual LILW wastes. This paper presents results from analyzing the samples of the bitumen waste material taken from the bulky bitumen block with waste salts loading 31 wt.% after storing the block in a shallow-ground repository for 12 years. Rich in natrium nitrate NPP-operational waste was incorporated in bitumen. Salts were separated from bitumen in some waste form samples. Non-homogeneous distribution of both salts and radionuclides was detected in vertical direction of the bitumen block. Specific radioactivity of the extracted bitumen was of the same order as the specific radioactivity of salts, in some cases even greater. Bitumen samples free of salts were further separated into three main bitumen fractions, asphaltenes, saturated and aromatic hydrocarbons, using methods of solvent extraction. Essentially all radioactivity of the bitumen was associated with the asphaltenc fraction. Aging of the bitumen waste form led to increase in asphaltene fraction content (with minimum 4%) and hardening of the waste material. The study has revealed a significant transfer of the waste salts radioactivity to the asphaltenc fraction of the bitumen matrix. Changes in the properties of (he bitumen waste form will be taken into consideration in modeling the long-term behavior of the bitumen waste materials under repository conditions.