STRUCTURAL INTEGRITY ANALYSIS OF THE STEAMDISTRIBUTION DEVICE IN CASE OF LOCA

摘要

The Ignalina NPP has a pressure suppressiontype of confinement, which is referred to as theAccident Localization System (ALS). The ALSprevents the release of the radioactive material fromthe NPP to the environment during a loss-of-coolantaccident (LOCA). Ten water pools arelocated in the two ALS towers (5 pools in eachtower), which separate the dry well from the wetwell. These water pools condense the accident-generatedsteam and prevent high overpressures inthe compartments.The steam distribution device (SDD), with thevertical vent pipes (nozzles) that are inserted underthe water of the condensing pools, connects the drywell and the wet well. In case of an accident, thesecomponents must be capable of withstanding thedynamic loads generated by a LOCA for successfulpressure suppression function.This paper presents the transient analysis ofthe SDD 9950×1600 in the first condensing pooland their connections to the vertical steam corridorsfollowing a maximal design basis accident(MDBA). A thermo-hydraulic analysis of the SDDwas performed using the state-of-the-artCOCOSYS code to determine pressure andtemperature histories resulting from a MDBA. Thefinite element code NEPTUNE was used toevaluate the structural integrity of the SDD and itssupporting reinforced concrete wall. Results showthat, although portions of the SDD 9950x1600undergo plastic response and the outside surface ofthe vertical steam corridor reinforced concrete wallcracks, the structural integrity of the SDD and wallare maintained during a MDBA.