VALIDATION OF CRITICAL PARAMETER CALCULATIONS FOR SODIUM DIURANATE USING SENSITIVITY AND UNCERTAINTY ANALYSIS

摘要

Periodically, UF6 cylinders are cleaned and recertified for continued use. A new process being developed to reconvert the uranium recovered from the heels produces a sodium diuranate (SDU) compound, Na_2U_2O_7. A processing facility or transportation packaging for SDU is an application area for which no critical benchmark data exists. The validation of calculational methods described in ANSI/ANS-8.1-1998; R2007 and further amplified by ANSI/ANS-8.24-2007 requires establishment of bias by correlating the results of critical and exponential experiments with results obtained for these same systems by the calculational method being validated. These validation requirements define the area(s) of applicability as follows: the limiting ranges of material compositions, geometric arrangements, neutron energy spectra, and other relevant parameters (such as heterogeneity, leakage, interaction, absorption, etc.,) within which the bias of a calculation method is established. Benchmark data may exists for experimental systems that are different from the SDU application with respect to material composition but "look" very similar from the standpoint of other parameters, in particular, physical and spectral indices, like hydrogen-to-fissile ratio (H/X), energy of average lethargy causing fission (EALF), enrichment, solution concentration. The application of S/U techniques allows for a formal estimation of the applicability of critical benchmark experiments with different material compositions to the application area of SDU compounds. This study presents an illustrative application of sensitivity and uncertainty analysis (S/U) procedures to the validation of criticality safety calculations for sodium diurante compounds. The S/U procedures used in this study are distributed in the Standardized Computer Analyses for Licensing Evaluation (SCALE) computer software system developed at Oak Ridge National Laboratory (ORNL) system.