Basing thermal hydraulic codes for nonstationary regimes of NPP with WWER

The modern NPP operation requirements as well as the requirements to safety basing lead to greater contribution of calculations in NPP designs. To base NPP operation capability and safety the issues of nonstationary thermal-hydraulic calculation results reliability and accuracy are of great importance. In Hydropress design bureau a special code complex for basing the operation capability and safety of NPP with WWER-440 and WWER-1000 with respect to nonstationary thermal-hydraulic processes has been developed. The major codes of this complex applicable to calculations of a power installation as a whole are DINAMIKA and TECH'-M. DINAMIKA code is employed for the analysis of nonstationary operation regimes and accidents of the 'minor leak' and 'steam pipeline rapture' types. To analyze accidents with the primary coolant loop tightness loss TECH'M code is used. The results of these codes basing are presented. It has been shown that the codes insure the realization of numerical algorithm stability criteria. The required accuracy of problem solutions is provided via the selection of computation schemes and integration steps over time. The accepted assumptions and correlations have been proved to obtain conservative calculation results as considered from the viewpoint of NPP operation capability and safety requirements. The directions of the code complex further improvement are discussed