ML22130A727
| ML22130A727 | |
| Person / Time | |
|---|---|
| Issue date: | 05/20/2022 |
| From: | Bhagwat Jain NRC/NRR/DORL/LPL4 |
| To: | |
| Jain B, NRR/DORL/LPL4 | |
| References | |
| Download: ML22130A727 (28) | |
Text
Expansion of Current Policy to Address Potential CommonCause Failures in Digital Instrumentation and Control Systems Advisory Committee on Reactor Safeguards Digital Instrumentation & Controls Subcommittee Briefing May 20, 2022
Technical Staff Presenters
- Samir Darbali - Electronics Engineer, NRR/DEX
- Norbert Carte - Senior Electronics Engineer, NRR/DEX
- Steven Alferink - Reliability and Risk Analyst, NRR/DRA Digital I&C Project Managers
- Bhagwat Jain - Senior Project Manager, NRR/DORL
- Michael Marshall - Senior Project Manager, NRR/DORL 2
Working Group Members
- NRR/DEX
- NRR/DORL
- Additional NRR/DEX
- Norbert Carte - Bhagwat Jain and DORL Support
- NRR/DRA - Sheldon Clark - Ming Li
- RES/DE - Michael Marshall
- Shilp Vasavada - Khoi Nguyen
- Sergiu Basturescu
- Sunil Weerakkody - David Rahn
- NRR/DSS - Richard Stattel
- Steve Wyman 3
Presentation Outline
- Introduction and Key Messages
- Background
- Subject and Purpose
- Proposed Expanded Policy
- Current Path
- RiskInformed Path
- Industry Proposal
- Status of Draft SECY Paper and Next Steps 4
Introduction
- SRMSECY93087 directs that, if the D3 assessment shows that a postulated CCF could disable a safety function, then a diverse means be provided to perform that safety function or a different function
- Diverse means may include manual actions
- The current policy does not allow for the use of a riskinformed approach to determine specific circumstances that would not require a diverse means for addressing DI&C CCF
- The SECY paper will provide recommended language for an expanded policy, which allows riskinformed approaches to address DI&C CCF 5
Key Messages
- The expanded policy will encompass the current points of SRMSECY93 087 (with clarifications) and expand the use of riskinformed approaches
- Any use of riskinformed approaches will need to be consistent with the Safety Goal Policy Statement, PRA Policy Statement, and SRMSECY98 0144
- The current DI&C CCF policy will continue to remain a valid option for licensees and applicants 6
Background - Early Concerns with CCF
- Early concerns with CCF
- CCF has been an NRC concern since the mid1960s
- In the early 1990s, the introduction of DI&C became a concern as a new source for introducing CCF, as explained in SECY91292
- Current DI&C CCF policy
- The NRCs current DI&C CCF policy is expressed in various documents, including SRMSECY93087; SECY180090; and BTP 719, Revision 8
- Current state of DI&C in the nuclear power industry
- Design development practices and quality assurance tools have evolved
- DI&C CCFs remains a serious area of concern 7
Background - Risk-Informing DI&C CCF
- Increased use of riskinformed decision making
- The staff is following the PRA Policy Statement and SRMSECY98144 to expand riskinformed decision making
- Modernizing the DI&C regulatory infrastructure
- SRMSECY160070 approved implementation of the staffs integrated action plan to modernize the NRCs DI&C regulatory infrastructure
- The staff issued guidance on riskinformed, graded approaches to address DI&C CCF for low safety significant safety systems (e.g., BTP 719 and RIS 200222, Supplement 1)
- The staff believes this is an appropriate time to expand the current policy on DI&C CCF to include the use of riskinformed approaches 8
SECY Paper Subject and Purpose
- SUBJECT
- Expansion of Current Policy to Address Potential CommonCause Failures in Digital Instrumentation and Control Systems
- PURPOSE
- Provide the Commission a recommendation on expanding the current policy to include the use of riskinformed approaches for addressing DI&C CCFs
- The recommended expanded policy will encompass the current positions in SRMSECY93087 and the use of riskinformed approaches to determine the appropriate level of defenseindepth and diversity to address DI&C CCF 9
Proposed Expanded Policy to Address DI&C CCF
- A single expanded policy that encompasses the current positions in SRM SECY93087 and provides for riskinformed approaches to address DI&C CCF
- The expanded policy includes:
- 1) Positions in points 1, 2, and 3 of SRMSECY93087 with appropriate clarifications and corrections from SECY180090
- 2) Language in point 4 of SRMSECY93087 with appropriate clarifications
- 3) The addition of riskinformed approaches to points 2 and 3 of SRMSECY93087
- The expanded policy provides for:
- 1) The deterministic demonstration of adequate diversity
- 2) Riskinformed approaches 10
Proposed Expanded Policy to Address DI&C CCF Proposed Expanded Policy to Address Digital I&C CCF Risk-Informed Current Path Path Point 1 The Risk-Informed Path allows The Current Path allows for the SRM-SECY-93-087, Point 1 for the use of risk-informed use of best estimate analysis (Clarified) approaches and other design and diverse means to address a techniques or defensive potential DI&C CCF. measures other than diversity to Point 2 SRM-SECY-93-087, Point 2 Point 2 address a potential DI&C CCF.
Risk-Informed Approach (Clarified)
Point 3 Point 3 SRM-SECY-93-087, Point 3 Risk-Informed Approach (Clarified)
Point 4 SRM-SECY-93-087, Point 4 (Clarified) 11
Current Path 12
Current Path
- The current policy continues to be a viable option to address DI&C CCF
- The current four points in SRMSECY93087 will remain as a viable path to licensees and applicants:
- Point 1 - assess the defenseindepth and diversity of the proposed I&C system to demonstrate that vulnerabilities to commonmode failures have adequately been addressed.
- Point 2 - analyze each postulated commonmode failure for each event that is evaluated in the accident analysis section of the safety analysis report (SAR) using best estimate methods demonstrate adequate diversity within the design for each of these events.
- Point 3 - If a postulated commonmode failure could disable a safety function, then a diverse means shall be required to perform either the same function or a different function.
- Point 4 - A set of displays and controls located in the main control room shall be provided for manual, systemlevel actuation of critical safety functions and monitoring of parameters that support the safety functions
- SECY180090 clarifies the application of the four SRMSECY93087 points and provides guiding principles that were used in the development of BTP 719, Rev. 8 13
Proposed Expanded Policy - Current Path Proposed Expanded Policy to Address Digital I&C CCF Risk-Informed Current Path Path Point 1 The Path allows for the use of SRM-SECY-93-087, Point 1 best estimate analysis and (Clarified) diverse means to address a potential DI&C CCF.
Point 2 Point 2 SRM-SECY-93-087, Point 2 Risk-Informed Approach (Clarified)
Point 3 Point 3 SRM-SECY-93-087, Point 3 Risk-Informed Approach (Clarified)
Point 4 SRM-SECY-93-087, Point 4 (Clarified) 14
Clarifying the Current Policy Language
- Replacing commonmode failure with commoncause failure
- The current language in SRMSECY93087 points 1, 2 and 3 uses the term commonmode failure when the intent and implementation is commoncause failure
- Adding facility where appropriate
- The current language in SRMSECY93087 points 1 and 2 focuses on the proposed I&C system, when the NRCs concern is on the defenseindepth and diversity of the facility incorporating the DI&C system
- Adding defenseindepth where appropriate
- The current language in SRMSECY93087 point 2 focuses on demonstrating adequate diversity, when the intent and implementation includes defensein depth 15
RiskInformed Path 16
Guiding Principles for Implementation
- The expanded policy will not conflict with existing regulatory requirements
- A rule change or exemption will not be required to implement it
- Expanding the DI&C CCF policy will be consistent with the agencys 1995 PRA Policy Statement, SRMSECY980144, and current focus for the agency to expand riskinformed decision making
- Implementation of the expanded DI&C CCF policy will continue to provide reasonable assurance of adequate protection and safety 17
Guiding Principles for Implementation (contd.)
- Applicants will need to address all five principles of riskinformed decision making, as listed in RG 1.174
- A systematic approach is used to evaluate DI&C failure causes during operation and maintenance, including inappropriate software behavior
- A PRA used for riskinformed approaches needs to be technically acceptable (e.g., meets the guidance in RG 1.200) and include an effective PRA configuration control and feedback mechanism 18
Proposed Expanded Policy - Risk-Informed Path Proposed Expanded Policy to Address Digital I&C CCF Risk-Informed Current Path Path Point 1 The Risk-Informed Path allows SRM-SECY-93-087, Point 1 for the use of risk-informed (Clarified) approaches and other design techniques or defensive measures other than diversity to Point 2 SRM-SECY-93-087, Point 2 Point 2 address a potential DI&C CCF.
Risk-Informed Approach (Clarified)
Point 3 Point 3 SRM-SECY-93-087, Point 3 Risk-Informed Approach (Clarified)
Point 4 SRM-SECY-93-087, Point 4 (Clarified) 19
SRM-SECY-93-087, Points 1 and 4 in the Risk-Informed Path
- SRMSECY93087, Point 1:
- It does not preclude the use of riskinformed approach for the D3 evaluation
- Existing policy and guidance support a graded approach and applying a level of rigor for the D3 assessment commensurate with the safety significance of the proposed DI&C system or component
- SRMSECY93087, Point 4:
- Regulations effectively require diverse and independent displays and controls
- Riskinformed approach to point 4 would not provide noticeable benefits 20
Risk-Informing the positions in SRM-SECY-93-087 Point 2
- Current approach focuses on consequences
- The staff considers this an appropriate area for riskinforming the evaluation of postulated DI&C CCFs
- A riskinformed approach can identify initiators or scenarios where lack of DI&C diversity does not compromise safety 21
Risk-Informing the Positions in SRM-SECY-93-087 Point 3
- Current approach only provides one way of addressing undesirable outcomes (i.e., diverse means)
- The staff considers this an appropriate area for evaluating design measures other than diversity to reduce the risk from a DI&C CCF 22
Benefits of Risk-Informed Approaches
- Riskinformed approaches can provide flexibility to address DI&C CCF and are consistent with the PRA Policy Statement
- Riskinformed approaches could support a graded approach in determining the degree of diversity that is needed
- PRA models could be used to systematically assess the need to reduce the risk introduced by the DI&C system
- Riskinformed approaches can have different levels of PRA use 23
Proposed Expanded Policy to Address DI&C CCF Proposed Expanded Policy to Address Digital I&C CCF Risk-Informed Current Path Path Point 1 The Risk-Informed Path allows The Current Path allows for the SRM-SECY-93-087, Point 1 for the use of risk-informed use of best estimate analysis (Clarified) approaches and other design and diverse means to address a techniques or defensive potential DI&C CCF. measures other than diversity to Point 2 SRM-SECY-93-087, Point 2 Point 2 address a potential DI&C CCF.
Risk-Informed Approach (Clarified)
Point 3 Point 3 SRM-SECY-93-087, Point 3 Risk-Informed Approach (Clarified)
Point 4 SRM-SECY-93-087, Point 4 (Clarified) 24
Key Messages
- The expanded policy will encompass the current points of SRMSECY93 087 (with clarifications) and expand the use of riskinformed approaches
- Any use of riskinformed approaches will need to be consistent with the Safety Goal Policy Statement, PRA Policy Statement, and SRMSECY98 0144
- The current DI&C CCF policy will continue to remain a valid option for licensees and applicants 25
Status of Draft SECY Paper and Next Steps
- The draft SECY is currently being developed
- A public outreach meeting is planned for June 2022
- The staff expects to send the SECY paper to the Commission in July 2022
- Upon approval of an expanded policy, the staff will proceed to update the implementation guidance in BTP 719 26
Questions?
Acronyms BTP Branch Technical Position NRC Nuclear Regulatory Commission CCF Common Cause Failure OEDO Office of the Executive Director for Operations D3 DefenseinDepth and Diversity PRA Probabilistic Risk Assessment DI&C Digital Instrumentation and Control RG Regulatory Guide ESFAS Engineered Safety Features Actuation System RIS Regulatory Issue Summary GDC General Design Criteria RPS Reactor Protection System IAP Integrated Action Plan SAR Safety Analysis Report I&C Instrumentation and control SECY Commission Paper MP Modernization Plan SRM Staff Requirements Memorandum NEI Nuclear Energy Institute