Extension of hybrid micro-depletion model for decay heat calculation in DYN3D code

Reactor dynamics code DYN3D, stand-alone or in coupling with plant thermo-hydraulic codes such as ATHLET or RELAP, is used to simulate transients and accidents scenarios. The radioactive decay heat generated by nuclear fuel after shutdown plays an important role in a number of accident scenarios. The decay heat model implemented in DYN3D so far is based on the German national standard DIN Norm 25463 (1990) and its applicability is limited to LWR fuel up to 4.1% enrichment.
This work extends the hybrid micro-depletion methodology, recently implemented in DYN3D, to the decay heat calculation by accounting explicitly for the heat contribution from the decay of each nuclide in the fuel. This method does not involve any assumptions about fuel content or operational history and therefore is valid for a wide range of fuel types. Detailed nuclide content of the fuel is calculated by DYN3D in a fuel cycle simulation, taking into account local operational history of each node. Thus, DYN3D is able to accurately calculate the axial decay heat power distribution in each fuel assembly during transients as well as in long term storage.