Reactor coolant system overpressure analysis during low temperature conditions for Qinshan phase II

When reactor primary system is single-phase water solid conditions, system overpressure may be caused by mass input or heat input. The overpressure case caused only by mass input is considered for Qinshan Phase-I, Framatome also only considers the overpressure case caused by heat input for Daya Bay design. But the design for Qinshan Phase-II is referenced to Daya Bay design (RCC-P is both adopted), its safety injection flowrate is greater than that of Daya Bay compared to primary coolant volume respectively, hence the overpressure caused by mass input should be analyzed besides the case caused by heat input. The Reactor Coolant System (RCS) will be protected by the safety valves of Residual Heat Removal system (RHR) under these two kinds of overpressure cases. The pressure of RCS and RHR is required to be less than 110% design pressure of RHR during transient, i.e. 5.11MPa, in order to ensure the RHR being in safety operation. This is the first time to analyze these two typical cases in China. It aims to demonstrate that the volume and set points of RHR safety valves meet the design criterion under overpressure cases during low temperature conditions for Qinshan Phase-II, consequently avoid RHR pressure exceeding the required value, and ensure the system in safety operation. (author)