Document: NUREG-0800
Document ID: 757b676a-0f71-4094-8677-ca3a50743281
Document Type: srp
Title: Revision 7 – August 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A344.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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Content:
s a diverse means of coping with AOOs BTP 7-19-5 Revision 7 – August 2016 and postulated accidents that are concurrent with a software CCF of the DI&C protection system. NUREG-0800, SRP Section 7.8, “Diverse Instrumentation and Control Systems,” describes the review process and additional acceptance criteria for diverse I&C systems provided to protect against CCF. 3. Purpose The purpose of this BTP is to provide guidance for evaluating an applicant’s D3 assessment, design, and the design of manual controls and displays to ensure conformance with the NRC position on D3 for I&C systems incorporating digital, software-based or software-logic-based RTS or ESF, auxiliary supporting features, and other auxiliary features as appropriate. This BTP has the objective of confirming that vulnerabilities to CCF have been addressed in accordance with the guidance of the SRM on SECY-93-087 and clarification provided in this staff guidance, specifically: • Verify that adequate diversity has been provided in a design to meet the criteria established by NRC guidance. • Verify that adequate defense-in-depth has been provided in a design to meet the criteria established by NRC guidance. • Verify that the displays and manual controls for plant critical safety functions initiated by operator action are diverse from digital systems used in the automatic portion of the protection systems. B. BRANCH TECHNICAL POSITION 1. Introduction 1.1. Echelons of Defense The NRC staff identified four echelons of defense in NUREG/CR-6303: • Control System - The control system echelon usually consists of equipment that is not safety-related that is used in the normal operation of a NPP and routinely prevents operations in unsafe regimes of NPP operations. • Reactor Trip System - The RTS echelon consists of safety-related equipment designed to reduce reactivity rapidly in response to an uncontrolled excursion. • Engineered Safety Features - The ESF echelon consists of safety-related