Zhouyu Liu

The pseudo-resonant-nuclide subgroup method based global–local self-shielding calculation scheme

ABSTRACT The pseudo-resonant-nuclide subgroup method (PRNSM) based global–local self-shielding calculation scheme is proposed to simultaneously resolve the local self-shielding effects (including spatial self-shielding effect and the resonance interference effect) for large-scale problems in reactor physics calculations. This method splits self-shielding calculation into global calculations and local calculations. The global calculations obtain the Dancoff correction factor for each pin cell by neutron current method. Then an equivalent one-dimensional (1D) cylindrical problem for each pin cell is isolated from the lattice system by preserving Dancoff correction factor. The local calculation is to perform self-shielding calculations of the equivalent 1D cylindrical problem by the PRNSM. The numerical results show that PRNSM obtains accurate spatial dependent self-shielded cross sections and improves the accuracy of dealing with the resonance interference over the conventional Bondarenko iteration method and the resonance interference factor method. Furthermore, because both global and local calculation is linearly proportional to the size of problems, the global–local calculation scheme could be applied to large-scale problems.

Development and Validation of Subchannel Code SUBSC

SUBSC was developed to simulate thermal–hydraulic phenomena in the core of pressurized water reactors, as well as innovative reactors operated with supercritical water as coolant. Both precise IAPWS-IF97 formulations and approximating polynomial correlations were implemented to calculate properties of water. A typical PWR fuel assembly problem, a supercritical water heat transfer experiment, and the steady state bundle benchmark of the pressurized water reactor subchannel and bundle tests (PSBT) were applied to validate this code. The SUBSC predicted results showed good agreement with experimental data and results obtained from COBRA, demonstrating feasibility and accuracy of this code. In order to improve efficiency, a restarted GMRES algorithm with preconditioning was implemented for solving the pressure correction equation. The numerical results showed the efficiency could be enhanced dramatically as the size of the problem being solved became large.

SCATTERING CORRECTION FOR IMAGE RECONSTRUCTION IN FLASH RADIOGRAPHY

Scattered photons cause blurring and distortions in flash radiography, reducing the accuracy of image reconstruction significantly. The effect of the scattered photons is taken into account and an iterative deduction of the scattered photons is proposed to amend the scattering effect for image restoration. In order to deduct the scattering contribution, the flux of scattered photons is estimated as the sum of two components. The single scattered component is calculated accurately together with the uncollided flux along the characteristic ray, while the multiple scattered component is evaluated using correction coefficients pre-obtained from Monte Carlo simulations.The arbitrary geometry pretreatment and ray tracing are carried out based on the customization of AutoCAD. With the above model, an Iterative Procedure for image restORation code, IPOR, is developed. Numerical results demonstrate that the IPOR code is much more accurate than the direct reconstruction solution without scattering correction and it has a very high computational efficiency.