Radiological consequence analysis of annulus ventilation system with delayed operation under severe accident of nuclear power plants

During severe accidents, for the nuclear power plants (NPPs) with double-containment design, if a sub-atmospheric pressure cannot be built or the accident filter cannot be activated when annulus ventilation system is failed to operate normally, the control function of fission-product release of dual containment would be weakened. With focus on the double-containment design adopted by most of the Gen-Ⅲ NPPs in the world, this paper firstly calculates the release amount of radioactive materials into environment under different delay scenarios of annulus ventilation system operation, with the consideration of the intact containment and using NUREG-1465 source term. Then the Criteria for Limited Impact(CLI) provided in European Utility Requirements (EUR) are applied to evaluate radiological consequence of severe accident, and the relationship between the delay of annulus ventilation system operation and 'large release' is analyzed. The results could be a reference for the emergency response actions and radiological consequence estimation in the context of severe accidents. (authors)