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atw Vol. 62 (2017) | Issue 6 ı June DECOMMISSIONING AND WASTE MANAGEMENT 406 | | Fig. 6. Correlation of measured and calculated Am-241 data with burnup for BE124 and BE210 fuel assemblies of Obrigheim NPP. difference II. The definition of Percentage difference II is similar to that of Percentage difference I, except that the code calculation results replace the Cs-137/U-238 values calculated from the nuclide composition data for the two nuclides (Cs-137, U-238). The 12 data points with percentage differences of up to −35 % can also be seen in the ‘Percentage difference II’ column. The ‘Percentage difference III’ column lists the differences between the code calculation results and the Cs-137/U-238 values calculated from the nuclide composition data for the two nuclides (Cs-137, U-238) divided by the calculated Cs-137/U-238 values. The magnitudes of the percentage differences in this column are less than 5 %, except for one case. Therefore, in the OECD/NEA SFCOMPO database, the nuclide composition data for these two nuclides (Cs-137, U-238) seem to be trustworthy, whereas the Cs-137/ U-238 data taken directly from the database can be suspected of including calculation errors. Recalculation of the Cs-137/U-238 data in the OECD/NEA SFCOMPO database using the measured data for the two nuclides (Cs-137, U-238) is recommended. in the percentage differences for Am-241 (up to 85 %) and Cm-242 (70 % for Karlsruhe and 45 % for Ispra). Gauld et al. [12] also indicated possible problems in back-calculating isotopic compositions to a reference date, using the measurement data of Am-241 for Takahama-3 NPP as an example. Note that most of the Am-241 (half-life = 432.6 years) at the time of measurement is from the decay of Pu-241 (half-life = 14.325 years). Figure 6 shows the correlation of the measured and calculated Am-241 data with the burnup for the BE124 and BE210 fuel assemblies at Obrigheim NPP. First, it was confirmed that the data provided in the OECD/ NEA SFCOMPO database are identical with those provided in the original data source, Barbero et al. [24]. Although a gradual increase in Am-241 quantities is expected as the burnup increases, as can be seen in the calculated data, a large variation is observed in the measured data as the burnup increases, especially when the burnup is 31.5 GWd/MTU ( GEROBRPWR-11). Some measured data, especially those within the ellipse in Fig. 6, appear to be inconsistent with other measured data. The measured Am-241 data were obtained by mass spectrometry or alpha spectrometry at Ispra or alpha spectrometry at Karlsruhe. All of the measured data that were found to be larger (sometimes significantly larger) than the calculated data, which are indicated by an ellipse in Fig. 6, were obtained by alpha spectrometry at Ispra. In addition, 8 of the 10 values measured by alpha spectrometry at Ispra are found in the ellipse. The measurement data obtained by mass spectrometry at Ispra and alpha spectrometry at Karlsruhe are found to be relatively close to the calculated data. Owing to the relatively high inaccuracy of the measured data obtained by alpha spectrometry at Ispra compared to the measured data obtained by mass spectrometry at Ispra and alpha spectrometry at Karlsruhe, as shown in Fig. 6, a detailed review of the measured data obtained by alpha spectrometry at Ispra seems to be necessary. Figure 7 shows the correlation of the measured and calculated Am-242 data from Obrigheim NPP with the burnup. Note that the scale of the measured data (left-hand Y-axis) is 10 times larger than that of the calculated data (right-hand Y-axis). Figure 7 shows that the measured Am-242 data are about 10 times larger than the calculated data for the seven samples from Obrigheim NPP. Because Cm-242 is produced by the decay of Am-242, the ratio of the halflives of Am-242 and Cm-242 provides information on the atomic ratio of the 3.4 Large uncertainty in Am-241 and large deviation in Am-242 As indicated in Fig. 3, a large uncertainty between the measured and calculated data for Am-241 and a large deviation between the measured and calculated data for Am-242 were observed. In a comparison of the measured and computed data for a sample from Obrigheim NPP, Fast et al. [5] also observed a high deviation | | Fig. 7. Correlation of measured and calculated Am-242 data from Obrigheim NPP with burnup. Decommissioning and Waste Management Validation of Spent Nuclear Fuel Nuclide Composition Data Using Percentage Differences and Detailed Analysis ı Man Cheol Kim
atw Vol. 62 (2017) | Issue 6 ı June | | Fig. 8. Ratios of measured Cm-242 data to measured and calculated Am-242 data for the seven samples from Obrigheim NPP. two nuclides in equilibrium. The halflives of Am-242 and Cm-242 are 16.02 hours and 162.8 days, respectively, and 82.70 % of Am-242 goes through beta decay to form Cm-242. Therefore, the measured values for Cm-242 are expected to be about 200 times larger than the measured values for Am-242 in equilibrium. Figure 8 shows the ratios of the measured Cm-242 values to the measured and calculated Am-242 values for the seven samples from Obrigheim NPP. Although the ratio of the Cm-242 values to the calculated Am-242 values is around 150, the ratio of the Cm-242 values to the measured Am-242 values is generally less than 20. Therefore, it is likely that the measured Am-242 values overestimate the actual quantity of Am-242 by about 10 times. Detailed analysis of how the measured Am-242 values were derived from the raw experimental data to the data provided in the OECD/NEA SFCOMPO database seems to be necessary. 4 Conclusions Nuclide composition data of spent nuclear fuels such as those provided in the OECD/NEA SFCOMPO database are important in many fields including reactor physics, fuel cycle applications, radiological consequence analysis, and nuclear forensics. To reduce unnecessary uncertainties associated with nuclide composition data, the validation of such data is a high-priority task. As one of the first steps, a simple method is proposed for identifying the nuclide composition data that may include errors and therefore require detailed analysis or further investigation. The proposed method is based on the ORIGEN-ARP code calculation, the assumption of a constant power history, the percentage differences of the calculated and measured composition data, and detailed analysis of the identified data. The application of the proposed method to the nuclide composition data of spent nuclear fuels from Obrigheim NPP demonstrated that the method can effectively identify various possible errors or data that need to be further investigated. Errors identified during detailed analysis or possible errors that require further investigation include: • Errors in burnup measurement (e.g., GEROBRPWR-9) • Errors in properly considering the cooling time (e.g., Pu-241/Pu-239) • Errors in the ratio calculation from measured data (e.g., Cs-137/ U-238) • Possible systematic errors in measurements of isotopic composition (e.g., Am-241 and Am-242 measurements at Ispra) Although the nuclide composition data that were not identified as needing detailed analysis or further investigation cannot necessarily be considered as definitively validated, it is believed that the proposed method can identify a significant portion of the errors in the nuclide composition data. Despite the simplicity of the proposed method, it is believed to be a very efficient method of identifying those nuclide composition data that require detailed analysis or further investigation. For this reason, the proposed method is expected to be useful as the first step in validation of nuclide composition data of spent nuclear fuels such as those in the OECD/NEA SFCOMPO database. Acknowledgements This work was supported by a grant from the Nuclear Safety Research Program of the Korea Foundation of Nuclear Safety, with funding from the Korean government's Nuclear Safety and Security Commission. This work was also supported by a grant from the Nuclear Research & Development Program of the National Research Foundation of Korea, which is funded by the Korean government's Ministry of Science, ICT & Future Planning (Grant Code: NRF-2016M2B2A9A02945211). References [1] https://www.oecd-nea.org/sfcompo/ [2] Masayoshi Kurosawa, Yoshitaka Naito, Hiroki Sakamoto and Toshiyuki Kaneko. The isotopic compositions database system on spent fuels in light water reactors (SFCOMPO), JAERI-Data/Code 96-036, Japan Atomic Energy Research Institute, February 1997. [3] H. Mochizuki, K. Suyama, Y. Nomura, H. Okuno. Spent Fuel Composition Database System on WWW – SFCOMPO on WWW Ver.2. Japan: Japan Atomic Energy Research Institute; 2001, Report no. JAERI-Data/Code 2001-020 [in Japanese]. [4] Yi-Kang Lee. Comparative Analysis of Isotopic Composition of Spent Fuel from Takahama-3 PWR PIE database using TRIPOLI-PEPIN Code, Proceedings of the ANS Topical Meeting on Reactor Physics Organized and hosted by the Canadian Nuclear Society (PHYSOR-2006). Vancouver, BC, Canada. September 10-14 2006. [5] Ivan Fast, Yuliya Aksyutina, Holger Tietze-Jaensch. Evaluation and Parameter Analysis of Burn up Calculations for the Assessment of Radioactive Waste, Proceedings of the WM2013 Conference, Phoenix, Arizona, USA, February 24-28, 2013. [6] G. Nicolaou. Discrimination of spent nuclear fuels in nuclear forensics through isotopic fingerprinting, Annals of Nuclear Energy, vol.72, pp.130-133, October 2014. [7] Kenya Suyama, Ali Nouri, Hirold Mochizuk, Yasushi Nomura. Improvements to SFCOMPO – a Database on Isotopic Composition of Spent Nuclear Fuel, Book of extended synopses of the International conference on storage of spent fuel from power reactors, Vienna, Austria, 2-6 Jun 2003. [8] Ian C. Gauld, Yolanda Rugama. Activities of the OECD/NEA Expert Group on Assay Data for Spent Nuclear Fuel, Proceedings of the International Workshop on Advances in Applications of Burnup Credit, Cordoba, Spain, 27-30 Oct 2009. DECOMMISSIONING AND WASTE MANAGEMENT 407 Decommissioning and Waste Management Validation of Spent Nuclear Fuel Nuclide Composition Data Using Percentage Differences and Detailed Analysis ı Man Cheol Kim
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