New calculations for nuclear reactor safety
The Monte Carlo method is a basic tool in particle transport problems that is well suited for tasks requiring detailed modelling of geometry and physics. It has been used in analyses of nuclear reactor behaviour for decades, but the applications have mainly been restricted by computer capacity. The 'High performance Monte Carlo reactor core analysis' (HPMC) project is extending the use of the method beyond steady-state problems such as shielding. Researchers found that it is feasible to analyse dynamic behaviour within reasonable computational time. Take for instance, the maximum power or temperature in an accident scenario. Nuclear reactor modelling is a complicated task that combines detailed description of neutron transport and coolant flow through the reactor core. Starting from the interactions between neutrons and the target nuclei, the intermediate step is the so-called lattice calculation, in which the geometry is modelled at the fuel rods assembly level. These were used as input parameters for a 3D reactor simulator, which yields the reactor response under different operating conditions. Using the Monte Carlo N-particle (MCNP) code, researchers were able to provide the spatial power distribution in the reactor, given information about temperature and coolant densities. The power distribution was then input to thermal-hydraulic calculations to produce more accurate estimates of temperature and coolant densities. These were fed back into the Monte Carlo calculations to update the power distribution.The inclusion of the thermal-hydraulic feedback also took Monte Carlo burn-up calculations several steps further. Burn-up calculations by the Serpent code provide a picture of changes in irradiated nuclear fuel. This allows the study of nuclear systems over long time periods ( typically, the fuel cycles of a nuclear power reactor. These have been successfully tested for different reactor core geometries. Throughout the project, special emphasis is being placed on finding ways to implement simple, efficient and fast solutions that will help speed up Monte Carlo calculations. When the Monte Carlo calculations are sufficiently fast, they will be more commonly applied by designers and operators on complex nuclear reactor problems.
Keywords
Nuclear reactor, safety, Monte Carlo method, fuel rod, coolant flow, neutron transport
