Development Of The Method For RPV Fast Neutron Fluence Calculation

This thesis discusses the application of Discrete Ordinates(SN) methods for reactor pressure vessel(RPV) neutron fluence calculations. As many commercial nuclear light water reactors(LWR) approach the end of their design lifetime, it is of great consequence that reactor operators and regulators be able to accurately characterrize the structural integrity of the RPV for financial reasons, as well as safety reasons, due to the possibility of plant life extensions. The structural integrity of the RPV is degraded by the bombardment of high-energy neutrons, and thus, in order to qualify the integrity, the neutron fuence at the RPV must be well known, The SN method, which can effectively solved the problems involving neutron deep penetration and high anisotropy, moreover, requires few computational process time for 3D reactor models computations, is employed. This thesis presents two models of the H.B. Robinson-2 and NUREG/CR 6115 benchmark for determination of RPV fluence.The methodology for determination of the 3D fluence distribution is based on the synthesizing or combination of transport calculations of 2D and 1D neutron flux distributions. All of the transport calculations were carried out using the DORT two-dimensional (SN) code and the BUGLE-96 cross-section library. In the transport analysis anisotropic scattering will be treated with a P3 expansion of the cross-sections and angular discretization will be modeled with an S8 angular quadrature. An energy-and space-dependent fixed distributed source based on fuel cycle specific core power, burnup, and enrichment distributions will be used.Detailed neutron flux solutions are provided at selected pressure vessel azimuthal, radial, and axial locations. neutrons spectrum and reaction rates with associated uncertainties are respectively provided in the surveillance capsule and at ex-vessel cavity dosimeter.This thesis introduce the least squares adjustment methods, which provide the capability of combining the measurement data with the neutron transport calculation resulting in a best estimate neutron energy spectrum with associated uncertainties. Best estimates for key exposure parameters such as fast neutron flux (E> 1.0 MeV) along with their uncertainties are then easily obtained from the adjusted spectrum.