Document: NUREG-0800
Document ID: f2ddec6c-0cce-4223-b813-233678ee07d0
Document Type: srp
Title: DIVERSE INSTRUMENTATION AND CONTROL SYSTEMS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159B171.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.8
CFR Part: 
CFR Title: 

Content:
rol room. • Completion of protective action - The ATWS mitigation logic and DAS should be designed such that, once initiated, the mitigation function will go to completion. • D3 analysis - The I&C functions credited with providing diversity should be consistent with the assumptions of the applicant or licensee’s D3 analysis. For 7.8-8 Draft Revision 6 – August 2015 example, diverse I&C system equipment should be environmentally qualified for the environments in which the D3 analysis assumes they will operate. When a D3 analysis is not provided, the following diversity criteria should be met: - Equipment diversity should be provided to the extent reasonable and practicable to minimize the potential for common-cause failures. - Equipment diversity is required from the sensors/transmitters to and including the components used to interrupt control rod power or vent the scram air header. - For interruption of control rod power, obtaining circuit breakers from different manufacturers is not, in and of itself, sufficient to provide the required diversity. - For mitigating systems other than diverse RTSs (e.g., auxiliary feedwater), diversity is required from the sensors to, but not including, the final actuation device. - Sensors need not be of a diverse design or manufacturer. - Existing RTS sensing lines may be used for ATWS mitigation instruments. - Sensors/transmitters and sensing lines should be selected such that adverse interactions with existing control systems are avoided. - Logic and actuation device power for the ATWS mitigation system should be from an instrument power supply independent from the power supplies for the existing RTS. Existing RTS sensor and instrument channel power supplies may be used, provided the possibility of common-cause failure is prevented. - If the ATWS system is explicitly addressed as part of a D3 analysis, the analysis provides the basis for assessing the adequacy of diversity between the ATWS mitigation system and the RTS.