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:
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 BTP 7-19-6 Revision 7 – August 2016 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. 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 thereby control) the following plant critical safety functions and conditions: 1. Reactivity control 2. Reactor core cooling and heat removal from the primary system 3. Reactor coolant system (RCS) integrity 4. Radioactivity control 5. Containment conditions 1.3 Combining RTS and ESFAS In addition to divisional independence, many earlier analog I&C architectures consisted of discrete and separate analog components in each echelon of defense. In digital systems, formerly discrete systems (e.g., the RTS and the ESFAS) could be combined into a single DI&C system. Digital systems that combine most, if not all, RTS and ESFAS functions within a single digital system using a limited number of digital components in both new NPP designs and upgrades to current operating plant systems could introduce new effects from single failures as well as CCF effects that do not exist in systems that use separate discrete components. While a single random