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Criticality Safety

SCALE provides a suite of computational tools for criticality safety analysis that is primarily based on the KENO Monte Carlo codes for eigenvalue neutronics calculations. Two variants of KENO provide identical solution capabilities with different geometry packages. KENO V.a uses a simple, efficient geometry package sufficient for modeling many systems of interest to criticality safety and reactor physics analysts. KENO-VI uses the SCALE Generalized Geometry Package, which provides a quadratic-based geometry system with much greater flexibility in problem modeling but with slower runtimes. Both versions of KENO perform eigenvalue calculations for neutron transport primarily to calculate multiplication factors (keff) and flux distributions of fissile systems in continuous energy and multigroup modes and are typically accessed through Criticality Safety Analysis Sequence with KENO V.a (CSAS5) and Criticality Safety Analysis Sequence with KENO-VI (CSAS6). The CSAS sequences implement XSProc to process material input and provide a temperature and resonance-corrected cross section library based on the physical characteristics of the problem being analyzed. If a continuous energy cross section library is specified, no resonance processing is needed, and the continuous energy cross sections are used directly in KENO, with temperature corrections provided as the cross sections are loaded.

A search capability is available with CSAS5 to find desired values of keff as a function of dimensions or densities. The two basic search options offered are (1) an optimum search seeking a maximum or minimum value of keff and (2) a critical search seeking a fixed value of keff. For continuous energy calculations, reaction rate tallies can be requested within the CSAS input, and for multigroup calculations, reaction rate calculations are performed using the KMART (KENO Module for Activity-Reaction Rate Tabulation) post-processing tools. A conversion tool is provided to up-convert KENO V.a input to KENO-VI either as a direct KENO input K5toK6, or more commonly, as a CSAS sequence C5toC6.

The Standardized Analysis of Reactivity for Burnup Credit using SCALE (STARBUCS) performs criticality calculations for spent fuel systems employing burnup credit. STARBUCS automates the criticality safety analysis of spent fuel configurations by coupling the depletion and criticality aspects of the analysis, thereby eliminating the need to manually process the spent fuel nuclide compositions into a format compatible with criticality safety codes. For burnup loading curve iterative calculations, STARBUCS employs the search algorithm from CSAS5 to determine initial fuel enrichments that satisfy a convergence criterion for the calculated keff value of the spent fuel configuration.

The Sourcerer sequence applies the Denovo discrete ordinates code to generate the starting fission source distribution in a KENO Monte Carlo calculation. This sequence is especially applied to burnup credit transportation and storage analysis of as-loaded canister of used fuel.