Severe accident management measures in VVER-91/99

The comprehensive safety concept for advanced Russian design VVER-91/99 covering accidents beyond the design basis have been developed within the defense-in-depth framework according to modern requirements for severe accident management (SAM). Normal operation systems and safety systems along with special engineered features, instrumentation and accident management procedures are to be employed for the accident management tasks. The current practical realization of the VVER-91/99 design is the twin units of Tianwan NPP in China designed by SPAEP and to be commissioned in 2004. Besides the requirements on the proven design solutions to be used, the General Contract for Tianwan NPP construction stipulates a number of extra requirements for the plant safety during beyond design basis accidents. The measures implemented in the VVER-91/99 design allow to prevent the core damage for many BDBA sequences involving additional failures compared with design basis. In case a design basis accident progresses into a severe accident, the considered measures and technical means of severe accident management mitigate its possible consequences and ensure meeting the radiation safety acceptance criteria. The safety targets for VVER-91/99 design including its beyond-design-basis domain meet the requirements not only of the Tianwan NPP contract, but also of the new Russian regulatory documents and the current IAEA and EUR recommendations. (author)