Severe accident codes status and future development

New demands for acceptance of nuclear power require full deterministic evidence of nuclear power plants (NPP) safety. From this point of view, the role of precise deterministic analysis of NPP safety plays a very important role for both the existing and future generation of NPPs. Considering the current status of existing severe accident codes, one may conclude that their capabilities are quite limited and not sufficient to prove NPP safety. This conclusion is based on the experience of usage of these codes, analysis of models and experimental database supporting codes and used for their validation. At the same time, the modern level of development of computer techniques and numeric methods allows the use of equations based on first principles rather than correlation. The transition to physical modeling appears to be more effective in the cases of designing and validation of codes using both separate effect and integral tests, and allows predictive power of codes to be increased and the range of uncertainties to be reduced. Moreover, physical modeling allows critical points of models and codes to be understood, and permits the planning of integral tests to resolve severe accident and accident management issues. (C) 1997 Elsevier Science S.A.