From a computing standpoint, flash X-ray radiography is much more time-consuming than traditional X-ray applications, and despite the constant increase of computing resources, methods to reduce the calculation time while preserving accuracy are highly needed. At the Commissariat à l'Energie Atomique, DIANE is the code devoted to flash X-ray calculations. After a brief description of the general features of DIANE, two selected methods implemented in DIANE to provide fast calculations are described. One concerns bremsstrahlung X-ray creation without electron transport electrons: the SSB model. The quality of this model is assessed within the framework of flash X-ray applications on two test problems with a fully photon-electron transport performed with MCNP5. The other focuses on particle tracking and Woodcock tracking. The performance of tracking within large meshes is evaluated.