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    Physically Constrained Adjustment of Calculated Neutron Spectra for Dosimetry and Vessel Locations


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    Modal (eigenvector) decomposition has been performed on the published neutron spectrum covariance matrices for Arkansas Nuclear One, Unit 1. The largest eigenvalue of the 15×15 correlation matrix is 10.97, and only five others exceed 0.15 (1% of the trace). The remaining nine eigenvalues are extremely small. Small values imply that some linear combinations of the fluences are almost invariant under any permissible adjustment. The invariance was enforced by setting the corresponding eigenvalues to zero. The non-zero eigenvalues that remain in this example represent the variances of the fluence within the vector space where adjustment can occur. It is shown that this procedure produces physically meaningful adjustments, without the need for complete prior covariance information. Included is consideration of the propagation of adjustments from the dosimetry location to the T/4 position within the reactor pressure vessel.


    neutron spectrum, adjustment, pressure vessel surveillance, least squares, covariance matrix

    Author Information:

    Williams, JG
    Professor, Univ. of Arizona, Tucson, AZ

    Griffin, PJ
    Principal Member of the Technical Staff, Sandia National Laboratories, Albuquerque, NM

    Committee/Subcommittee: E10.08

    DOI: 10.1520/STP13634S