Comp23/Nuctran user's guide. Proper version 1.1.6

NUCTRAN is a fast multiple path model that calculates nuclide transport in the near field of a repository as occurring through a network of resistances and capacitances coupled together like an electrical circuit network. The model, which is a very coarsely discretized integrated finite difference model, was devised to be very fast and compact by embedding analytical solutions at sensitive zones. The code allows the user to simultaneously consider a multitude of pathways by which the nuclides are transported by diffusion to the flowing water in fractures surrounding the barrier system. The nuclide dissolution may be calculated using two approaches, a solubility limit approach or a congruent dissolution approach. The conceptual model used in NUCTRAN can be represented by three bodies. The bodies are the source, the barrier system, and the sinks. The source is defined as a well-mixed compartment. The barrier system is the physical medium by which the nuclides migrate to reach the sinks located in the surrounding system or outside of the region considered as the barrier system. The sinks, considered as recipients where the water flows, are fully defined by a local equivalent flow rate. The purpose of this document is to assist the user in managing problems with NUCTRAN. An overview of the theory, numerical method, and the code designed to solve the problem are presented. Finally, an example is handled in detail