ANALYSIS OF LARGE CORE NEUTRONICS BY THE MONTE CARLO METHOD COUPLED WITH THERMAL HYDRAULICS

摘要

Power reactor cores of PWR, BWR, SFR or HTR are composed of assembly lattices containing lattices of fuel pins or other structures such as coated particles. For the simulation of the neutron transport the geometry and material composition even of large full size cores can be modeled in detail by Monte Carlo codes such as MCNP6 using appropriate geometry options. Generally, except for fresh cores at BOL, the fuel composition varies due to enrichment and burnup in the different fuel pins and the fuel, moderator or coolant temperatures and densities vary according to power distribution and cooling conditions. A realistic neu-tronics analysis should account for thermal-hydraulic parameters. For a full core analysis the number of cells with different nuclide compositions and temperatures can be very large and needs an effective assignment of material specifications and temperatures to the cells. Therefore, instead of the standard input for material and temperature assignment to cells, an assignment is used which overrides input parameters during particle tracking. The temperature dependency of continuous energy resonance cross sections is taken into account by a polynomial fit (OTF) and for thermal neutron scattering laws by interpolation. The thermal-hydraulic parameters will be calculated by the system code ATHLET for liquid coolants and ATTICA-3D for gaseous coolant. An over-relaxation algorithm is used to improve convergence between neutronics and thermal hydraulics calculation. Examples will be shown for different applications for LWRs with square and hexagonal lattices, sodium cooled fast reactors (SFR) with hexagonal lattices and HTRs.