The research and implementation of the stretch-out operation in Daya Bay Nuclear Power Station

Stretch-out operation mode (SO) can deepen the reactor burnup when boron concentration is near to 0 ppm, which introduce the additional reactivity be reducing the moderator temperature and the load decreasing. Stretch-out is used for the nuclear power plant in some nuclear power plants in the world, but in chine, so had no the experience before 2003. The main purpose of Stretch-out operation in Daya Bay Nuclear Power Station is to extend inspection shutdowns in order to achieve an optimum arrangement between Daya Bay and Ling Ao Nuclear Power Stations. Stretch-out operation also increases the economic of the fuel. As a specific operation mode, which outruns the original reactor core design, the related and specialized design justification and safety analysis is required. At the end of reactor operation cycle, boron concentration is approaching to 0 ppm, all the control bank is out of the core, surplus reactivity is exhausted. Stretch-out operation implies the continuous or stepwise reduction of load and moderator temperature. As a consequent, the neurotic measurement system and the reactor control and protection system parameters should be modified specially for the stretch out operation. According to the requirement of the grid electricity production arrangement, the first stretch-out operation implemented from March 12 to March 21 2003. Although it was just 9 days, however, it is successfully to avoid the overlapping between 209 and 109 inspection shutdowns in Daya Bay Nuclear power station, and additional 30 GWH energies were produced. At the same the much more important things is that we obtained the experience for longer time stretch out operation in the future. (author)