bnpp

In this article, the use of annular fuel instead of solid fuel is investigated in the core of the Bushehr reactor. In annular geometry, the fuel has two internal and external channels and two surfaces for temperature exchange. The current solid fuel used in the Bushehr reactor and five types of annular geometries were simulated in the MCNPX.2.6.0 nuclear code. After validating the simulation, some neutronic parameters have been calculated by the code. By analyzing the results, the optimal annular geometry has been introduced and suggested. After the neutronic analysis, the chosen annular geometry has been analyzed from the thermohydraulic point of view in the COBRA code and FLUENT software. According to the obtained results, the use of annular fuel, the burnup increases by about 4.01 GWd/MTU. Also annular fuel usage decreases the maximum temperature of the fuel center by about 300 K. It also increases the safety margin of MDNBR from 1.7 in solid fuel, to 2.5 in the outer cladding, and to 3.7 in the inner cladding of annular fuel.

There are different parameters such as increase or decrease of heat removal from primary circuit which affect the coolant mixing phenomena in the vessels of pressurized water reactors (PWRs). Determination of mixing level is very important from reactor safety and control aspects. In this study, the thermal hydraulic test of coolant mixing within the reactor pressure vessel of Bushehr nuclear power plant (BNPP) has been simulated (3-D modeling) using ANSYS CFX 18.0. In this test, the fluid mixing due to primary circuit heat removal decrease has been investigated and the goal of this research has been defined as finding the coolant temperature distribution, computing the primary circuit loops mixing coefficients and other thermal hydraulic parameters of coolant in the whole reactor zones specially the reactor core which is the most important. To achieve this, the geometry of whole reactor considering all components have been modeled and the governing equations of reactor flow field (the Reynolds Averaged Navier-Stokes equations utilizing SST k-ω turbulence model) have been solved in CFX. Comparison of simulation results and experimental results of BNPP startup test shows the average error of 6.45 % and 10.92 % for mixing coefficient of loops and core inlet, respectively. According to the implemented simplifications, the results have good accuracy.