The basic design and plant systems has been described in Part 1 of this article (Nuclear Future, Volume 01, No.3). Part 1 defined the AP1000 as an advanced pressurised water reactor (PWR) capable of producing approximately 1100MWe output, which received Final Design Approval from the US Nuclear Regulatory Commission (USNRC) on 13 September 2004. Design Certification is expected later in December 2005.

The AP1000 design has been assessed by BNFL and British Energy for UK deployment and has been determined to be a viable option for the UK. Part 2 of the article describes the AP1000’s Control & Instrumentation Systems and explains how these systems provide protection against unsafe reactor operation during steady-state and transient power operations and initiate selected protective functions to mitigate the consequences of design basis events. The authors explain that, because of the rapid changes which are taking place in the digital computer and graphic display technologies employed in a modem human system interface, design certification of the AP1000 focuses upon the process used to design and implement control and instrumentation systems for the AP1000, rather than on the specific implementation. The detailed design of the AP1000 C&I will be based on the C&l platforms available at the time of plant order but the paper does make proposals for any near-term order. The C&I systems for the AP1000 are based on advanced digital technology and the use of processorbased systems.

The principal C&l systems are:

• The protection and safety monitoring system detects off-nominal conditions and actuates appropriate safety functions necessary to achieve and maintain the plant in a safe condition

• The plant control system provides the functions necessary for normal operation of the plant, as well as control of the non-safety defence-in-depth systems.

• The diverse actuation system provides an alternate means of initiating reactor trip and actuating selected engineered safety features and providing plant information to the operator.

This article, in its entirety, describes the passive safety systems of the AP1000, the C&l architecture, and the design of the principal C&I systems. The paper focuses on how the concepts of diversity and defence-in-depth are used to meet USNRC and EPRI (US utility) safety goals.