STRUCTURAL INTEGRITY ANALYSIS OF THE STEAM DISTRIBUTION DEVICE IN CASE OF LOCA

摘要

The Ignalina NPP has a pressure suppression type of confinement, which is referred to as the Accident Localization System (ALS). The ALS prevents the release of the radioactive material from the NPP to the environment during a loss-of-coolant accident (LOCA). Ten water pools are located in the two ALS towers (5 pools in each tower), which separate the dry well from the wet well. These water pools condense the accident-generated steam and prevent high overpressures in the compartments. The steam distribution device (SDD), with the vertical vent pipes (nozzles) that are inserted under the water of the condensing pools, connects the dry well and the wet well. In case of an accident, these components must be capable of withstanding the dynamic loads generated by a LOCA for successful pressure suppression function. This paper presents the transient analysis of the SDD 9950×1600 in the first condensing pool and their connections to the vertical steam corridors following a maximal design basis accident (MDBA). A thermo-hydraulic analysis of the SDD was performed using the state-of-the-art COCOSYS code to determine pressure and temperature histories resulting from a MDBA. The finite element code NEPTUNE was used to evaluate the structural integrity of the SDD and its supporting reinforced concrete wall. Results show that, although portions of the SDD 9950×1600 undergo plastic response and the outside surface of the vertical steam corridor reinforced concrete wall cracks, the structural integrity of the SDD and wall are maintained during a MDBA.