## 2 Materials and Methods
### Target Radionuclides  
The radionuclides to be analyzed were selected using the radionuclide selection method, applied to the decommissioning of the Rancho Seco [3] and Zion [4] NPPs in the U.S., for 37 radionuclides detected in the Wolsong Unit 1 pressure tube specimens from a study on the evaluation of heavy water reactor source terms [11]. As a CANDU-type heavy water reactor, the Wolsong Unit 1 is composed of 380 nuclear fuel channels and each nuclear fuel channel is comprised of a pressure tube and calandria tube. The calandria tube acts as the pressure and thermal shielding boundary between the heavy water moderator and the coolant channel, whereas the pressure tube supports the nuclear fuel at the pressure boundary and nuclear reactor core to maintain the pressure so that the coolant does not boil. The pressure tube is made of Zr alloy containing 2.5% of Nb, with a total length, inner radius, outer radius, and density of 6.4 m, 5.2 cm, 5.6 cm, and 6.6 g-cm\({}^{-3}\), respectively [11]. According to the Wolsong Unit 1 source term evaluation report, 37 radionuclides were derived from the preliminary evaluation of the radioactivity of the pressure tube using the ORIGEN2 code for 9 pressure tube specimens of the Wolsong Unit 1 [11]. When considering the License Termination Plan (LTP) of the Rancho Seco power plant, nuclides with a half-life of fewer than 2 years were excluded from the target radionuclides because their effect on the result was considered insignificant [3]. Thus, based on ICRP 107 [12], among the 37 radionuclides derived above from the pressure tube of the Wolsong Unit 1, 10 radionuclides were found to exhibit a half-life of fewer than 2 years (\({}^{54}\)Mn, \({}^{90}\)Y, \({}^{108}\)Ag, \({}^{109}\)Cd, \({}^{109}\)Ag, \({}^{1250}\)Te, \({}^{137}\)Ba, \({}^{182}\)Ta, \({}^{192}\)Ir, and \({}^{192}\)Ir), while the remaining 27 radionuclides exhibited a half-life of 2 years or longer. Therefore, this study also excluded radionuclides with a half-life of fewer than 2 years from the evaluation by applying the sample case of the Rancho Seco LTP. Further, a study related to the decommissioning of the Zion NPP in the U.S. reported a list of relative fractions of radionuclides based on the attenuation-corrected radioactivity concentration for the list of nuclides detected in 19 samples collected from the Zion NPP site [4]. Consequently, on analyzing the 27 target radionuclides while referring to the literature [4] related to the decommissioning of the Zion NPP and the result of the preliminary evaluation of the radioactivity of pressure tube specimens from the Wolsong Unit 1, 12 radionuclides (\({}^{3}\)H, \({}^{14}\)C, \({}^{55}\)Fe, \({}^{60}\)Co, \({}^{63}\)Ni, \({}^{90}\)Sr, \({}^{93}\)Zr, \({}^{93}\)Nb, \({}^{94}\)Nb, \({}^{108}\)Ag, \({}^{121}\)Sm, and \({}^{125}\)Sb) were found to exhibit a half-life of 2 years or longer with a relative fraction of 0.01% or higher. The sum of their relative fractions was ca. 99.42%. In contrast, another 15 radionuclides yielded a relative fraction of less than 0.01% with the sum of their relative fractions being ca. 0.02%. Furthermore, the sum of relative fractions of the other 10 radionuclides with a half-life of fewer than 2 years was calculated to be ca. 0.56% [11]. In this study, the 25 radionuclides with a relative fraction of less than 0.01% were excluded from evaluation owing to the small sum of their fractions, which exerts a negligible effect on the result. Furthermore, in addition to the 12 radionuclides for analysis, the radionuclides \({}^{134}\)Cs and \({}^{137}\)Cs, which were detected in the previous study on the Kori Unit 1, Rancho Seco, and Zion NPPs, were included; thus, 14 radionuclides were finally selected as the target of analysis, and they are listed in Table 1 [3,4,13].