T. Iida

Y. "Sakuma

Y." Ogata

National Institute for Fusion Science (NIFS-Repository)

§8. Removal of Impurities from Environmental Water Samples for Tritium Measurement by Means of Liquid Scintillation Counter Sakuma, Y., lida, T. (Department of Nuclear Engineering, Nagoya University), Ogata, Y. (Faculty of Medicine, Nagoya University) Liquid scintillation counting is now the most popular method to measure the tritium concentration in the low level water sample such as environmental water samples. However, it takes much time with a lot of doing to distill off the impurities in the sample water before mixing the sample with the liquid scintillation cocktail. In the light of it, we investigated the possibility of an alternative method with membrane filters for purification. In Japan, measurements of tritium concentrations in the terrestrial and subterranean water and rainwater are now carried out in many laboratories by means of the official tritium analyzing method. According to the method, distillation is essential to avoid misestimaion caused by quenching, chemical luminescence and other radioactive substances[!]. However, because of the following four reasons, a possible alternative using the membrane filter was investigated. [a]. The distillation method takes much time and labor to distill off and wash out the used utensils. [b]. Such substances as those which have lower boiling points and not very higher ones than boiling point of water can hardly be removed because you need to heat enough to vaporize the water thoroughly. [ c] . Generally you have scarcely any quenchable substances in the environmental water samples. [d]. Scintillation cocktail as known a non-quenching liquid has been on the market lately. As the result, the filtration method was proved to be available to be alternatively used for tritium measurement. We also tried to apply the filtration method, when we concentrate the water sample using the electrolysis enrichment apparatus. We found out that the method was also available to use before and after the enrichment[2]. 416 Table 1, Comparison of Filtration Methods Filtration Method Filtration Limit [ nm] Micro Filtration 100 Ultra Filtration 10 Nano Filtration 1 Reverse Osmosis 0.1 Co~rison of Rermval Methods for Tritium Enrichrrent G) Distillation and Enrichrrent r-------, i. -\ ' ::.\ ~-::· (Z) Reverse Q;rrosis and Enrichrrent (-<J.Sday) Tritium enrtchment fur-3days ~ ~'G~G ~~ Scintillation Sart1JieScintilation detection 65mL cocktal6fmL for 1500 min (-<J.Sday) Fig. I Comparison of Removal Methods for Tritium Enrichment References [1] Radioactive Measurement Series Volume 9 "Tritium Analyzing Method", Science and Technological Agency of Japan (1997). [2] SAKUMA Y. et al, Proc. IRPAIO, P-4a-248 (2000) 

Removal of Impurities from Environmental Water Samples for Tritium Measurement by Means of Liquid Scintillation Counter

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