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atw Vol. 62 (2017) | Issue 6 ı June 402 DECOMMISSIONING AND WASTE MANAGEMENT [8] Department of Homeland Security (2015). Cyber security Framework Implementation Guidance for U.S. Nuclear Power Reactors. Available at: https://www.us-cert.gov/sites/default/ files/c3vp/framework_guidance/ nuclear-framework-implementationguide-2015-508.pdf. Validation of Spent Nuclear Fuel Nuclide Composition Data Using Percentage Differences and Detailed Analysis Man Cheol Kim 1 Introduction Nuclide composition data of spent nuclear fuels are important in many nuclear engineering applications. In reactor physics, nuclear reactor design requires the nuclide composition and the corresponding cross sections. In analyzing the radiological health effects of a severe accident on the public and the environment, the nuclide composition in the reactor inventory is among the important input data. Nuclide composition data need to be provided to analyze the possible environmental effects of a spent nuclear fuel repository. They will also be the basis for identifying the origin of unidentified spent nuclear fuels or radioactive materials. The Spent Fuel Isotopic Composition (SFCOMPO) database [1–3], which was originally developed by the Japan Atomic Energy Research Institute and is now managed by the Organization for Economic Co-operation and Development/Nuclear Energy Agency (OECD/ NEA), provides measured nuclide composition data of spent nuclear fuels. The SFCOMPO database has been widely used to validate computer codes and nuclear data libraries for spent fuel and fuel cycle applications. For example, Lee [4] validated TR4PEP, a depletion code combining the continuous-energy Monte Carlo transport code TRIPOLI-4.3 and the point depletion code PEPIN-2, using the Takahama-3 post-irradiation examination results provided in the SFCOMPO database. Fast et al. [5] compared the code calculation results obtained using SCALE 6.0 and 6.1 with measurement data from Obrigheim nuclear power plant (NPP) to investigate the validity of the correlations for burnup calculations involving key nuclides such as Cs-134, Cs-137, and Eu-154. Nicolaou [6] tested the potential of isotopic fingerprinting for nuclear forensics purposes using the measurement data provided in the SFCOMPO database. With the recognition of the importance of extending the SFCOMPO database, the Expert Group on Assay Data of Spent Nuclear Fuel Authors Sébastien Champigny MBA, Dipl.-Phys., M.Eng. Product manager cyber security for critical infrastructures Deeksha Gupta M.Sc. in Nuclear Sci. & Tech. Cyber security PhD Candidate (EGADSNF), which is in charge of main taining the OECD/NEA SFCOMPO database, is trying to obtain new assay data that are not open to the public or are open but not widely available. Suyama et al. [7] mentioned that the use of the OECD/NEA framework was intended to facilitate the collection of new data from member countries. Possible candidates for newly added data are summarized in Gauld and Rugama [8] and the state-of-the-art report by EGADSNF [9]. For this purpose, Suyama et al. [10] provided additional measurement data from Ohi-1 and Ohi-2 with detailed information and specifications so that they can be added to the SFCOMPO database. Raap et al. [11] reported on the expansion of the SFCOMPO database by the addition of measured data from CANDU reactors, MAGNOX reactors, VVERs, and RBMKs for use in developing isotopic signatures for nuclear forensics purposes. As the EGADSNF admitted in the state-of-the-art report [9], measurement data were added to the SFCOMPO database as reported by laboratories, without peer review. Validation of the data to assess the quality of the measurements is con sidered a priority task for improvement of the SFCOMPO database. The measurement data in the SFCOMPO database have been validated in several recent studies. Venesa Watson Master in Computer Forensics Cyber security PhD Candidate Dr. Karl Waedt Senior expert Cyber Security Concepts & Architecture AREVA GmbH Paul-Gossen-Straße 100 91052 Erlangen, Germany Gauld et al. [12] described the recent experience of Oak Ridge National Laboratory in validating the measured isotopic composition data of spent nuclear fuel. Among the 118 PWR experimental assay data, 87 (73.7 %) were from the SFCOMPO database. Gauld et al. [12] reported problems such as highly erratic Am-241 measurement data from Takahama-3 due to possible errors in the adjustment of the time of discharge and physically impossible measurement results due to possible typographical errors. However, the details on how the SFCOMPO database should be revised are not clearly described. Okumura et al. [13] described how the measurements of Se-79, Tc-99, Sn-126, and Cs-135 for the Cooper, Calvert Cliffs-1, and H. B. Robinson-2 reactors in the SFCOMPO database should be revised by applying the latest nuclear data, especially the half-lives of the four nuclides. For example, the calculatedto-experimental value for Se-79 changed from 5.5 to 0.92 after the application of the latest half-life of Se-79 provided by Bienvenu et al. [14]. This paper proposes a simple method for analysis and validation of nuclide composition data of spent nuclear fuels such as those found in the SFCOMPO database. The proposed method consists of a simplified code calculation, the assumption of a 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. 1. Distribution of U-235 initial enrichment and burnup of 246 samples in OECD/NEA SFCOMPO database. constant power history, comparison of the measured data and code calculation results, and detailed analysis of those data that deviate significantly from other data to identify the causes of the deviations. During such a crosscheck process, many, if not all, of the errors in either the measured data or the code calculations could be identified. The proposed method is described in Section 2. The application of the proposed method to nuclide composition data of spent nuclear fuels from Obrigheim NPP is described in Section 3, and the identified data and associated findings are analyzed in detail. Section 4 presents the conclusion of this paper. 2 Approach to validation of nuclide composition data 2.1 Overview of the data in the SFCOMPO database The OECD/NEA SFCOMPO database provides 10,282 measurement data from 246 samples of nuclear fuels irradiated in 14 reactors. Figure 1 shows the distribution of the U-235 initial enrichment and burnup of 246 samples in the SFCOMPO database. The initial enrichment ranges from 1.45 wt % for the samples from Fukushima-Daiichi-3 and Monticello to 4.11 wt % for those from Takahama-3, and is concentrated in the range from 2.5 to 3.5 wt %. The burnup ranges from 2.21 to 71.84 GWd/MTU. Note, however, that the samples from Monticello show exceptionally high burnup (exceeding 40 MWd/MTU) despite the low initial U-235 enrichment. Owing to this abnormal overburn of low-enriched fuels, Hermann et al. [15] rated the data from Monticello as ‘not recommended.’ If the samples from Monticello are excluded, the burnup ranges from 2.21 to 47.3 GWd/MTU. 2.2 Approach to validation Nuclide composition data of spent nuclear fuels such as those in the OECD/NEA SFCOMPO database can be validated using the percentage differences between the computed and measured compositions of each isotope in each sample. Here, the percentage difference is defined as the calculated value minus the measured value, divided by the measured quantities or ratios, as follows: (1) The percentage difference has been used in many code validation studies such as those of Hermann et al. [16], DeHart and Hermann [17], and Jang et al. [18]. By reviewing the percentage differences of nuclide compositions or ratios, candidates for detailed analysis can be identified. The identified candidates can be subjected to detailed analyses such as consistency checks as a function of burnup or parent–daughter pairs, as performed by Gauld and Rugama [8], and the original data sources can be reviewed. 2.3 Code calculations As mentioned in the state-of-the-art report by EGADSNF [9], evaluation of the measured data in the SFCOMPO database requires significant effort and is therefore a significant but challenging objective of future activities of the EGADSNF. Thus, using simplified models in code calculations would be more efficient for performing a large number of code calculations in a manageable and unified way than using detailed models. For this reason, code calculations were performed using ORIGEN-ARP [19,20]. Consequently, the code calculations were performed mainly based on important parameters such as the fuel assembly type, initial enrichment, burnup, operation history, and cooling time of the samples. Fast et al. [5] compared the code calculation results of the ARP model (simple and fast) and the NEWT model (compli cated and precise) for a sample from Obrigheim NPP and found that the percentage differences for most nuclides are within 20 % for the APR model and within 10 % for the NEWT model. To make code calculations for a large number of samples, the use of ORIGEN-ARP provides an efficient way of calculating nuclide compositions with sufficient precision. 2.4 Consideration of operation history The degree of detail in the irradiation history varies among the 14 reactors in the OECD/NEA SFCOMPO database. Very detailed information on the cycle number, elapsed time, time interval, core power density, bundle power density, and so on is provided for Cooper NPP. On the other hand, no information is available for JPDR-I, Tsuruga-1, and Takahama-3 NPPs in the SFCOMPO database. The operation history of Takahama-3 NPP is available in NUREG/CR-6798 [21]. Research has found that code calculations of nuclide compositions are not significantly affected by the detailed power history. Chabert et al. [22] and Nakahara et al. [23] compared the nuclide compositions of spent fuels obtained using the accurate power history and an assumed constant power history, and found that the principal uranium and plutonium isotopes and other fission products are not significantly affected by the power history. Based on these findings, a constant power history was assumed as a reasonable approximation instead of the accurate power history, which was available for only a limited number of samples. 3 Application to Obrigheim NPP Nuclide Composition Data A total of 1,153 nuclide composition or nuclide ratio data were provided for 23 samples from Obrigheim NPP. The samples were analyzed at two different laboratories, Ispra and Karlsruhe. Ispra analyzed 17 samples, and Karlsruhe analyzed 10 samples. DECOMMISSIONING AND WASTE MANAGEMENT 403 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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