A technique for code validation for criticality safety calculations Page: 2 of 24
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A Technique for Code Validation for Criticality Safety Calculations
H. R. Dyer, W. C. Jordan and V. R. Cain
There are probably as many techniques to validate computer codes for criticality
safety purposes as there are computer codes and code validators. One method used at
Martin Marietta Energy Systems, Inc., to validate the KENO code and associated cross
sections consists of determining a single-sided, uniform-width, closed-interval, lower
tolerance band for k., of critical systems.,2 For application, this lower tolerance band
becomes the upper safety limit (USL) acceptance criteria for subcriticality based upon
the KENO calculations. A system is considered acceptably subcritical if a calculated kg
plus 2 standard deviations lies below this upper safety limit (i.e., kff + 2a < USL).
The technique requires determining the linear-least-squares fit of the data, k(x) =
bo + bx, as a function of some independent variable and determining the variance of the
data fit, s2,). A multiplier, C, of the standard deviation of the fit is determined such that
there is at least a confidence that a proportion, P, of the population (of future
calculations of critical systems) will lie above the line defined by k(x) -Cs,). The a
confidence is defined by a = 1 - y,/2 - Y2 , where (1 - y,) is the one-sided confidence
band about the linear regression and (1 - Y2) is the confidence on the variance of the fit.
The width of the tolerance band depends not only on the values selected for P
and a, but also on the range of the independent variable, x, the number of data points, n,
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Dyer, H.R.; Jordan, W.C. (Oak Ridge National Lab., TN (United States)) & Cain, V.R. (Oak Ridge Y-12 Plant, TN (United States)). A technique for code validation for criticality safety calculations, article, January 1, 1991; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1060412/m1/2/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.