Aging of a Bitumen Waste form in Wet Repository Conditions
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AGING OF A BITUMEN WASTE FORM IN WET REPOSITORY CONDITIONS M.I. OJOVAN, N.V. OJOVAN, Z.I. GOLUBEVA, I.V. STARTCEVA, A.S. BARINOV Scientific and Industrial Association ‘Radon’, the 7-th Rostovsky Lane 2/14, Moscow, RF, Fax: (095) 248 1941, E-mail: [email protected] ABSTRACT 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 asphaltene 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 asphaltene fraction of the bitumen matrix. Changes in the properties of the bitumen waste form will be taken into consideration in modeling the long-term behavior of the bitumen waste materials under repository conditions. INTRODUCTION Bitumen is a widely used encapsulation material for various radioactive wastes. For decades it has been used in Russia and some former Soviet Union republics for solidification of liquid wastes of low and intermediate activity arising from the operation of nuclear power plants (NPP). They include sludges, evaporator concentrates and ion-exchange resins containing short-lived radionuclides (137Cs, 134Cs, 60Co, 90Sr) and minor amounts of longlived radionuclides (mainly 239Pu). Sodium nitrate-rich wastes represent a significant part of the sludges and concentrates. Bituminized NPP waste is being stored in on-site waste vaults. In Russia industrial bituminisation plants have also been used at SIA ‘Radon’ facilities for conditioning the radwaste originating from the use of radioactive materials in medicine, industry and research. Bituminized wastes have been placed for storage in shallow-ground repositories. There is a lack of data on long term behaviour of bitumen waste materials. This places uncertainty on the predictions of repository performance and safety. Long term leach tests is a way to help solve the problem. A 12yr leach test of bituminized waste material has been performed at the SIA ‘Radon’ and the results
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