On Depth In Defense And Diverse Of Common Cause Failrue Of Digital System In Nuclear Power Station

The earliest instrument and control system instrument and control(I&C)in nucear power plant use simulation technology and the discrete I&C devices. With the continuous development of digital technology and gradually mature, digital I&C technology has been widely used in nuclear power stations. In general, digital I&C system consists of hardware and software, hardware and simulation equipment have similar characteristics and fault type. However, due to the software applications and software interaction between redundant divisions leading to reduce the ability against the Common Cause Failure(CCF), and I&C system of nuclear power station have from hardware to software for CCF defensive problems. So in the process of the digital system design in nuclear power stations should focus on the defense of CCF and the application of defense in depth and diversity(D3), especially for the Generations III nuclear power stations should be more attention.This paper research and analysis the CCF in I&C system, summarize the types and formation mechanism, and put forward D3 defense method against CCF. Then,D3 technology,including the concept, requirements and the necessity,are analyzed, and the D3 technology applied in digital I&C system of the generations III power plant are analyzed, the characteristics of the D3 technology in digital system is summarized. And then combine with CCF and D3 in digital I&C system of the generations III power plant are analyzed for CCF defensive approach and technical difficulties. Finally, based on the fault tree analysis method, the D3 system and non-D3 system respectively model fault tree to evaluate and analyze the ability of defense and block for D3 against CCF, This paper found the D3 system failure probability was lower than that of the D3. On D3 of CCF of digital I&C system in the generations III power plant, D3 application in digital I&C system of the generations III power plant can be effective defensive CCF to reduce the harm and influence.To some extent, the reliability and safety of digital I&C system can be improved, and the design ability of domestic DCS platform is also promoted.the conclusion of the paper should provide a reference for DCS platform localization.