[en] Sodium cooled LMR core is comprised of many duct assemblies which have no flow exchanges between them. So, the required flow to each assembly corresponding to its power has to be allocated in thermal hydraulic design. Flow allocation facility, which is called orifice, is used for this purpose in an LMR core. In this context, flow grouping module for an LMR core has been developed. This report describes the modeling and method of this module, and explains the calculation procedure and the sample calculation results. Firstly, LMR core thermal hydraulic conceptual design and analysis procedure was explained in chapter 1. Chapter 2 overviews this flow grouping module, and in chapter 3 core design and configuration data with power distributions were given. The calculation modeling and method of this module were explained in chapter 4, and chapter 5 shows calculation procedure and sample calculation results. KALIMER breeder core design data, e.g., inlet and outlet temperatures, power distributions and core flow, were used in this report to explain how this module works. And this module works in the environment of Microsoft Excel 2000 of MSOffice 2000