Analysis of Radionuclide Migration Behavior in Loess Medium
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ANALYSIS OF RADIONUCLIDE MIGRATION BEHAVIOR IN LOESS MEDIUM WANG Zhiming, LI Shushen, GUO Zede, ZHAO Yingjie LI Zhentang, LI Shengfang ChinaInstitutefor RadiationProtection P.O.Box 120 Taiyuan, Shanxi, 030006, China
Tadatoshi YAMAMOTO, Shinichi TAKEBE, Hiromichi OGAWA Tadao TANAKA, Masayumi MUKAI Japan Atomic Energy Research Institute Tokai-mura, Naka-gun, Ibaraki-ken, Japan
ABSTRACT A five-year cooperative research program has been carried out by China Institute for Radiation Protection and Japan Atomic Energy Research Institute to develop safety assessment methodology for disposal of low level radioactive waste. Migration 85 3 behavior of radionuclides H and Sr through field tests, simulation tests in the laboratory and determination of distribution coefficients is discussed and analyzed in this paper. The results show that the retardation coefficients, Rd , from field tests are about 0.08-3.3 times those from simulation tests and Rd from batch tests are 1.1-44 times 85 those from field tests for Sr and loess medium. It was observed from field tests that radionuclides moved mainly downward under artificial sprinkling and a part of them moved up besides downward under natural rain condition. In addition, it was discovered that the retardation coefficient, Rd , increases with velocity of unsaturated water flow, u, in the analysis. 1. Experimental
Aerated zone is a natural barrier to retard transport of radionuclides released from shallow land repository. Moreover, radionuclide migration in the natural barrier is one of the important aspects interest in safety assessment. In order to develop safety assessment methodology for disposal of low level radioactive waste (LLW) a five-year cooperative research program has been fulfilled by China Institute for Radiation Protection (CIRP) and Japan Atomic Energy Research Institute (JAERI). Radionuclide migration behavior in the environmental medium can be studied through field tests, simulation tests in the laboratory and determination of distribution coefficients. An important parameter, retardation coefficient, Rd which describes radionuclide migration behavior, was obtained by using the three methods mentioned above in order to understand 85 Sr transport mechanism in the loess medium. The field tests were conducted at the CIRP's field test site located in semi-arid region in which evaporation rate is close to precipitation. Hence infiltration amount of water through aerated zone is small[1,2]. The field tests were conducted in 6 pits (Pits A-F) dug in unsaturated loess medium (see Fig.I)[3-6]. In order to observe their considerable Mat. Res. Soc. Symp. Proc. Vol. 353 01995 Materials Research Society
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vertical distribution, artificial sprinkling with a rate of 1.5 cm/d was also adopted in the tests besides natural rain condition to accelerate radionuclide migration. Under both 3 60 Co, 8 5 Sr and conditions, the tracers buried at 30 cm and 100 cm in depth are H, 13 4 Cs. During the tests, soil cores were periodically collected by collecting tube to determine verti
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