Abstract
It has been observed that the Reactor Coolant System (RCS) flowrate dissymmetry phenomenon (i.e. imbalance of primary flowrates between loops) appears in several Nuclear Power Plant (NPP) units. As an initial condition of fault studies, the RCS flowrate is very important to nuclear safety. The consequences of RCS flowrate dissymmetry are rarely investigated so far, and thus worthy of studying. This paper aims to analyze the safety margin of Pressurized Water Reactor (PWR) under specific accidents. A plant model is set up and accidents due to malfunction of a component in a single loop are simulated, in order to figure out whether Departure from Nucleate Boiling (DNB) is probable to happen. The results show that the Departure from Nucleate Boiling Ratio (DNBR) criterion is met for Partial Loss of Primary Flow accident with margins. For Main Steam Line Break accident, the flow dissymmetry has little impact on the accident consequences and the minimum DNBR meets the requirements. The Feedwater Line Break accident consequences are sensitive to the primary loop flowrate, while Departure from Nucleate Boiling (DNB) is not probable to happen with dissymmetry larger than 1500 m3/h. The results prove that the plant has enough safety margins and is able to operate under limited flow dissymmetry situation.
