Development and Assessment of a Diversity and Defense-in-Depth Strategy for the TerraPower TWR-P Advanced Nuclear Power Plant

The purpose of this paper is to provide an overview of the development and assessment of the Diversity and Defense-in-Depth (D3) strategy for the TerraPower Traveling Wave Reactor-Prototype (TWR-P) advanced nuclear power plant. The TWR-P digital control system (DCS) is currently being designed by TerraPower. The instrumentation and control (I&C) design and configuration were based on standard digital control products. The control systems making up the DCS were selected because of their applicability to the functions required by TerraPower and the U.S. Nuclear Regulatory Commission. The installation of a digital-based plant protection system and other systems throughout the TWR-P enhances safety in many areas when compared to the previous generation of analog-based instrumentation systems.

Nuclear facilities have increased their use and reliance on digital technology in systems and equipment (e.g., I&C, electrical systems, and fluid systems). In addition to I&C, examples of safety-related equipment that may use digital technology include emergency diesel generators, pumps, valve actuators, motor control centers, breakers, priority logic modules, time-delay relays, and uninterruptible power sources.

In the United States and around the world, engineering and licensing activities in standards and guidance have been, and are being, developed to address this important consideration in protecting safety-related systems. This paper addresses the latest in standards and guidance development as well as a review of the application of this guidance in the specific case cited.