Explicit decay heat calculation in the nodal diffusion code DYN3D

3D reactor dynamic code DYN3D was developed for analysis of transients and accident scenarios. The residual radioactive decay heat plays an important role in some of accident scenarios and in DYN3D it is taken into account by a model based on German national standard DIN Norm 25463. The applicability of this model is limited to a low enriched uranium dioxide fuel for light water reactors.
This paper describes the new general decay heat model implemented in DYN3D. The radioactive decay rate of each nuclide in each spatial node is calculated and the cumulative released heat is used to obtain the decay power spatial distribution for any time step. Such explicit approach is based on first principles and is free from approximations which limit its applicability. The proposed method is verified against Monte Carlo reference calculations.