Study On The Anti-Inadvertent-Dilution Modification In Qinshan Phase Ⅱ Nuclear Power Plant

Ever since the accident of Chernobyl Nuclear Power Plant, the research on reactivity insertion accident is becomes renewedly the focus in the nuclear industry. The nuclear regulation authority requests to checkup all the reactivity insertion accident in Safety Analysis Reports, and related safety system, safety precautions (including Emergency Operation Procedures) and inherence safety of the core to mitigate the reactivity insertion consequence in nuclear power plants.Boron dilution accident is among the accidents that must be paid attention to in nuclear power plant operation. China National Nuclear Safety Administration(NNSA) requested that modifications releated to the anti-inadvertent-dilution protection must be included in the nuclear island design of Qinshan phase II extension project. In order to keep consistent with extension project and raise the safety level, antidilution modification must be implemented in unit 1 and 2 in the near future.Based on the design of Unit 1 and 2 in Qinshan phase II nuclear power plant, the mechanism of boron diluton accident occurrence and the source term leading to boron diluton accident are analyzesd in detail in the thesis . The preventive measures against boron dilution accident and operator actions after occurance of the accident are studied in such aspects as engineering design, operation management and accident treatment as well. Meanwhile, a preliminary safety analysis on the accident is carried out, and possibility of boron dilution accident occurrence at Uint 1 and 2 due to human errors is pointed out. Moreover, the PSA analysis to the units according to the modification scheme is delivered, which concludes that the anti-inadvertent-dilution modifications in Unit 1 and 2 would promote the core safety margin effectively.In order to mitigate the consequence of inadvertant boron dilution accident or reduce the possibility of the accident, a feasibility analysis on the anti-inadvertent-dilution modifications is made and a preliminary blueprint is defined. It is expected that the study in this thesis would provide the anti-inadvertent-dilution modifications of Unit 1 and 2 in Qinshan phase II nuclear power plant with applicable measures, and offer a beneficial reference to post-modification document updating.