核电站仪控系统阈值判决及应用

基于物理参数的仪控系统阈值判决是核电站仪控系统的重要功能。常规阚值判决固定单一,缺乏与时间、工况的相关性。通过分析已有阈值判决,提出了在安全前提下采用阈值判决优化,在数据处理、阈值浮动、与工况相关联等方面作出改进,提升了仪控系统的容错、故障诊断能力,降低了停堆次数。     

Thermal-mixing analyses for safety injection at partial loop stagnation of a nuclear power plant

When a cold HPSI (High Pressure Safety Injection) fluid associated with an overcooling transient, such as SGTR (Steam Generator Tube Rupture), MSLB (Main Steam Line Break) etc., enters the cold legs of a stagnated primary coolant loop, thermal stratification phenomena will arise due to incomplete mixing. If the stratified flow enters the downcomer of the reactor pressure vessel, severe thermal stresses are created in a radiation embrittled vessel wall by local overcooling. As general thermal-hydraulic system analysis codes cannot properly predict the thermal stratification phenomena, RG 1.154 requires that a detailed thermal-mixing analysis of PTS (Pressurized Thermal Shock) evaluation be performed. Also, previous PTS studies have assumed that the thermal stratification phenomena generated in the stagnated loop side of a partially stagnated primary coolant loop are neutralized in the vessel downcomer by the strong flow from the unstagnated loop. On the basis of these reasons, this paper focuses on the development of a 3-dimensional thermal-mixing analysis model using PHOENICS code which can be applied to both partial and total loop stagnated cases. In addition, this paper verifies the fact that, for partial loop stagnated cases, the cold plume generated in the vessel downcomer due to the thermal stratification phenomena of the stagnated loop is almost neutralized by the strong flow of the unstagnated loop but is not fully eliminated.