In loosely coupled systems the criticality calculations using the traditional Monte Carlo power generation methods can lead to incorrect effective multiplication factor and neutron distribution functions, which is largely due to the steady-state neutron source in system. In reactor systems, the power generation method ensures the correct neutron source formation with a proper eigenfunction for any initial neutron distributions. A traditional power generation method does not guarantee the adequate source formation in loosely coupled systems even under very large calculation statistics. To count the neutron distribution functions in loosely coupled systems in TDMCC code is implemented algorithm based on fission matrix. Its capabilities are demonstrated to count the fission rate distributions in loosely coupled system such a slab with extended inhomogeneous fuel zones.

The computational methods of improved accuracy for neutronic process simulation in modern codes cause the new problems to substantiate the calculated characteristics and final errors, that requires the new approaches and computational tools. The traditional comparison of Calculation and Experiment results is often impossible due to the incompleteness of description of the experiment, the lack of necessary experimental data and underestimation of the experimental errors. In addition, verification of modern neutronic codes requires significantly more “reference” data than those, presented in benchmarks. The objective difficulties to obtain the experimental data of desired accuracy in the right amount necessitate the additional means for modern code benchmarking. A computational experiment, providing the “interval” values for key characteristics can be useful tool when testing modern neutronic codes under advanced simulation conditions. The problem of benchmarking is considered for nuclide kinetics problems when using the full element basis of fission products yields. The Computational Experiment is used to simulate the experiment with uranium sample irradiation in BN-350 reactor under conditions of incomplete description of the Physical Experiment.