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David Bernard

Publications and source records attributed to David Bernard.

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Measurement of Spectrum Averaged Cross Sections in LR-0 Benchmark Reference Neutron Field

The measured and evaluated excitation functions are fundamental quantities that affect the accuracy of all calculations in nuclear applications. Some cross sections, such as 14N(n,p)14C, have added value for special applications, as these reactions may be responsible for possible contamination in industrial processes such as spent fuel reprocessing. For the validation of the evaluated cross sections, we can rely on the comparison of the calculated spectrum averaged cross sections (SACS) for the given neutron spectrum with the measured SACS value. The benchmark reference neutron field has been identified, characterized, and well validated in the LR-0 special core. A very large set of SACS measurements in the LR0 reference field is measured with low uncertainty, making it an excellent set for deconvolution codes validation. The impact of the gamma-induced reaction on the production yield of neutron-induced reactions was investigated for most of the benchmarked reactions. Gamma competition was found to contribute at most 1% for the 197Au(n,2n) reaction, while being substantially lower for other target isotopes and neutron-induced activation reactions.

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Calculation and Verification of Irradiation Damage Cross Section with Energy-Angular Distribution

To complete the computation of Displacements per Atom (DPA) cross sections, the present work shows the methods of calculating DPA cross sections with the nuclear data of energy-angular distribution in both the laboratory and the Center-of-Mass (CM) frames. The method of direct calculation with data in the CM frame is proposed and recommended to decrease the computation burden and keep all information. Theoretical analyses reveal that more than 7-point Gauss-Legendre Quadrature (GLQ) should be used to ensure the convergence of the angular integration for DPA computations. Numerical results show that 8-point GLQ is sufficient for the continuum inelastic neutron scattering, while 64-point GLQ is implemented in NJOY. Because the integrand over secondary energy is not derivable in the whole domain of the secondary energy, the trapezoidal integration is used to perform the numerical integration. The numerical calculations show that the trapezoidal integration is suitable to perform the integration over the secondary energy on the fine grid given by nuclear data files at least for 56Fe. The present work reveals that the direct interpolation of energy-angular-integrated damage can give the same results computed with standard interpolated energy-angular distributions. The DPA cross sections will be overestimated if isotropic angular distributions are assumed. However, the first-order Legendre polynomial can give DPA cross sections within 0.4% deviation, while 12 orders are required to describe the anisotropic angular distribution.

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