In decommissioning process of nuclear facilities, large amount of radioactive isotopes are discharged as waste. Radioactive carbon isotope (14 C) is one of the key nuclides to determine the upper limit of concentration in the waste disposal. In particular, 14 C on the graphite reactor decommissioning should be separated from stable carbon isotopes (12 C and 13 C) and monitored for the public health and safety. We propose an isotope analysis system based on cavity ring-down laser spectroscopy (CRDS) to monitor the carbon isotopes (12 C, 13 C and 14 C) in the isotope separation process for the graphite reactor decommissioning. This system is compact and suitable for a continuous monitoring, because the concentration of molecules including the carbon isotope is derived from its photo absorbance with ultra high sensitive laser absorption spectroscopy. Here are presented the necessary conditions of CRDS system for 14 C isotope analysis through the preliminary experimental results of 13 C isotope analysis with a prototype system.

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (12 C 16 O 2 , 13 C 16 O 2) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm À1 (1.6 mm). The isotopic ratio has been obtained as ð1:07AE0:13ÞÂ10 À2 , in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3Â10 À8 cm À1 .

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide ( 12 C 16 O 2 , 13 C 16 O 2 ) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm À1 (1.6 mm). The isotopic ratio has been obtained as ð1:07AE0:13ÞÂ10 À2 , in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3Â10 À8 cm À1 .