Dynamic response analysis of corrosion products activity under steady state operation and Mechanical Shim based power-maneuvering transients in AP-1000

Abstract

The advanced Mechanical Shim (MSHIM) core control strategy is a flexible power-maneuvering feature of AP-1000 reactor. This is vulnerable for variation in Activated Corrosion Products (ACPs) buildup while providing frequent power maneuver opportunities. It is therefore important to study the ACPs buildup behavior in AP-1000 reactor. A new simulation methodology is developed to analyze the specific activity due to ACPs under steady state operation and MSHIM based power-maneuvering transients. The dynamic response of coolant specific activity due to corrosion products (56Mn, 59Fe, 24Na, 60Co and 99Mo) has been analyzed under steady state full power operation. It is observed that short-lived 56Mn and 24Na are major sources of predominant and total coolant specific activity during reactor operation, whereas long lived ACPs mainly contributed after shutdown. The parametric study of MSHIM control based daily load follow operation, step load, load regulation and scram transients is also carried out. It is found that specific activity increases or decreases directly as a function of power maneuvering levels during daily load follow and load regulation transients. However, if power becomes constant followed by the decreasing power maneuvering, the specific activity retains its prior behavior and finally attains a lower constant value. For the step load transients, the specific activity value increases sharply and finally reaches a new saturation level. In all of the anticipated power maneuvering transients, the post saturation specific activity value shows direct relation with net change in power before and after the transients. The higher the difference between pre-transient and post-transient power levels, the longer it takes to achieve saturation value and vice versa. For postulated scram transients, it is observed that the specific activity due to 56Mn suddenly decreases after the transients mainly due to its short half-life and discontinuation in further production.