Document: NUREG-0800
Document ID: dc63e8aa-2a74-4078-9e19-9a26ed1b4d8c
Document Type: srp
Title: Revision 6 – July 2012
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1105/ML110550791.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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dance 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 equipment that removes heat or otherwise assists in maintaining the integrity of the three physical barriers to radioactive release (cladding, vessel and primary cooling system, and containment) and the logic components used to actuate this safety-related equipment, usually referred to as the ESF Actuation System, and controls. ● Monitoring and Indicator System - The monitoring and indicator system echelon consists of sensors, safety parameter displays, data communication systems, and independent manual controls relied upon by operators to respond to NPP operating events. Revision 6 – July 2012 BTP 7-19-6 1.2 Plant Critical Safety Functions As described in NUREG-0737, Supplement No. 1, “Clarification of TMI Action Plan Requirements,” sufficient information should be provided to the nuclear reactor operators to monitor (and