ML17137A019

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NEI 96-07 Appendix D Draft Revision 0 - Proposed Revisions - May 16, 2017 Redline
ML17137A019
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Site: Nuclear Energy Institute
Issue date: 05/17/2017
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Nuclear Energy Institute
To:
Office of Nuclear Reactor Regulation
Holonich J J, NRR/DPR, 301-415-7297
References
NEI 96-07
Download: ML17137A019 (56)
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NEI PROPOSED REVISIONS (Document Date:

May 16, 2017)

NEI 96-07, Appendix D Draft Revision 0c

Nuclear Energy Institute SUPPLEMENTAL GUIDANCE FOR APPLICATION OF 10 CFR 50.59 TO DIGITAL MODIFICATIONS

NEI PROPOSED REVISIONS (Document Date:

May 16, 2017)

May 2017 NEI PROPOSED REVISIONS (Document Date:

May 16, 2017)

ACKNOWLEDGMENTS NEI would like to thank the NEI 01-01 Focus Team for developing this document.Although everyone contributed to the development of this document, NEI would like to give special recognition to David Ramendick, who was instrumental in preparing this document.

NOTICE Neither NEI, nor any of its employees, members, supporting organizations, contractors, or consultants make any warranty, expressed or implied, or assume any legal responsibility for the accuracy or completeness of, or assume any liability for damages resulting from any use of, any information apparatus, methods, or process disclosed in this report or that such may not infringe privately owned rights.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 i EXECUTIVE

SUMMARY

NEI 96-07, Appendix D, Supplemental Guidance for Application of 10 CFR 50.59 to Digital Modifications, provides focused application of the 10 CFR 50.59 guidance contained in NEI 96-07, Revision 1, to activities involving digital modifications. The main objective of this guidance is to provide all stakeholders a common framework and understanding of how to apply the 10 CFR 50.59 process to activities involving digital modifications. The guidance in this appendix supersedes NEI 01-01/ EPRI TR-102348, Guideline on Licensing of Digital Upgrades.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-1 TABLE OF CONTENTS EXECUTIVE

SUMMARY

...................................................................................................................................... i 1 INTRODUCTION ........................................................................................................................................ 2 1.1 B ACKGROUND .................................................................................................. 2 1.2 P URPOSE ........................................................................................................

32 2 [NOT USED] ................................................................................................................................................ 3 3 DEFINITIONS AND APPLICABILITY OF TERMS ............................................................................... 3 4 IMPLEMENTATION GUIDANCE .......................................................................................................

... 43 4.1 APPLICABILITY ...............................................................................................

43 4.2 SCREENING ...................................................................................................... 4 4.3 EVALUATION PROCESS ................................................................................ 2423 5.0 EXAMPLES.......................................................................................................................................... 5552 NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-2 1 INTRODUCTION 1.1 B ACKGROUND Licensees have a need to modify existing systems and comp onents due to the growing problems of obsolescence, difficulty in obtaining replacement parts, and increased maintenance costs. There also is great incentive to take advantage of modern digital technologies which offer potential performance and reliability improvements. In 2002, a joint effort between the Electric Power Research Institute (EPRI) and the Nuclear Energy Institute (NEI) produced NEI 01-01, Revision 0 (also known as EPRI TR-102348, Revision 1), Guideline on Licensing Digital Upgrades: A Revision of EPRI TR-102348 to Reflect Changes to the 10 CFR 50.59 Rule, which was endorsed (with qualifications) by the Nuclear Regulatory Commission (NRC) in Regulatory Issue Summary (RIS) 2002-22. Since the issuance of NEI 01-01 in 2002, digital modifications have become more prevalent. Application of the 10 CFR 50.59 guidance contained in NEI 01-01 has not been consistent or thorough across the industry, leading to NRC concern regarding uncertainty as to the effectiveness of NEI 01-01 and the need for clarity to ensure an appropriate level of rigor is being applied to a wide variety of activities involving digital modifications. NEI 01-01 contained guidance for both the technical development and design of digital modifications as well as the application of 10 CFR 50.59 to those digital modifications. The NRC also identified this as an issue and proposed separating technical guidance from 10 CFR 50.59 related guidance. EPRI document 3002005326, Methods for Assuring Safety and Dependability when Applying Digital Instrumentation and Control Systems, has been created to provide technical guidance for the development and design of digital systems with the pu rpose of systematically identifying, assessing, and managing failure susceptibilities of I&C systems and components. However, the use of EPRI 3002005326 is not required for the application of the 50.59-related guidance in this appendix.

NEI 16-16, Guidance for Addressing Digital Common Cause Failure has been created to provide technical guidance for addressing Common Cause Failure (CCF) for compliance to deterministic licensing criteria and NRC policies and positions such as SRM-SECY-93-087 and BTP 7-19. The technical-focused guidance contained in NEI 16-16, used in conjunction with the licensing-focused guidance in this document, provides a complimentary set of NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-3 approaches and considerations when implementing a digital modification. However, the use of NEI 16-16 is not required for the application of the 50.59-related guidance in this appendix.

1.2 P URPOSE Appendix D is intended to assist licensees in the performance of 10 CFR 50.59 reviews of activities involving digital modifications in a consistent and comprehensive manner. This assistance includes guidance for performing 10 CFR 50.59 Screens and 10 CFR 50.59 Evaluations. This appendix does not include guidance regarding design requirements for digital activities. The guidance in this appendix applies to 10 CFR 50.59 reviews for both small-scale and large-scale digital modifications-from the simple replacement of an individual analog meter with a microprocessor-based instrument, to a complete replacement of an analog reactor protection system with an integrated digital system. Examples of activities considered to be a digital modification include computers, computer programs, data (and its presentation), embedded digital devices, software, firmware, hardware, the human-system interface, microprocessors and programmable digital devices (e.g., Programmable Logic Devices and Field Programmable Gate Arrays). This guidance is not limited to "stand-alone" instrumentation and control systems. This guidance can also be applied to modifications or replacements of mechanical or electrical equipment if the new equipment makes use of digital technology (e.g., a new HVAC design that includes embedded microprocessors for control). Finally, this guidance is applicable to digital modifications involving safety-related and non-safety-related systems and components and also covers "digital-to-digital" activities (i.e., modifications or replacements of digital-based systems). 2 [NOT USED] This section is not used for digital modifications.

3 DEFINITIONS AND APPLICABILITY OF TERMS There are no definitions or modifications to the definitions necessary for application of 10 CFR 50.59 to digital modifications.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-4 4 IMPLEMENTATION GUIDANCE 4.1 APPLICABILITY There is no Applicability guidance unique to digital modifications.

4.2 S CREENING

Throughout this section, references to the main body of NEI 96-07, Rev. 1 will be identified as "NEI 96-07." As stated in NEI 96-07, Section 4.2.1, the determination of the impact of a proposed activity (i.e., adverse or not adverse) is based on the impact of the proposed activity on UFSAR-described design functions. To assist in determining the impact of a digital modification on a UFSAR-described design function, the general guidance from NEI 96-07 will be supplemented with the digital-specific guidance in the topic areas identified below. In the following sections and sub-sections that provide the Screen guidance unique to the application of 10 CFR 50.59 to digital modifications, each section and sub-section addresses only a specific aspect, sometimes at the deliberate exclusion of other related aspects. This focused approach is intended to concentrate on the particular aspect of interest and does not imply that the other aspects do not apply or could not be related to the aspect being addressed. Initially, all aspects need to be considered, with the knowledge that some of them may be able to be excluded based on the actual scope of the digital modification being reviewed. Within this appendix, examples are provided to illustrate the guidance. Unless stated otherwise, a given example only addresses the aspect or topic within the section/sub-section in which it is included, sometimes at the deliberate exclusion of other aspects or topics that, if considered, could potentially change the Screen conclusion. CAUTION The guidance contained in this appendix is intended to supplement the generic Screen guidance contained in the main body in NEI 96-07, Section 4.2. Namely, the generic Screen guidance provided in the main body of NEI 96-07 and the more-focused Screen guidance in this appendix BOTH apply to digital modifications.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-5 4.2.1 Is the Activity a Change to the Facility or Procedures as Described in the UFSAR? There is no regulatory requirement for a proposed activity involving a digital modification to default (i.e., be mandatorily "forced") to an adverse conclusion. Although there may be adverse impacts on UFSAR-described design functions due to the following types of activities involving a digital modification, these typical activities do not default to an adverse conclusion simply because of the activities themselves:

  • The introduction of software or digital devices.
  • The replacement of software and/or digital devices with other software and/or digital devices.
  • The use of a digital processor to "calculate" a numerical value or "generate" a control signal using software in place of using analog components.
  • Replacement of hard controls (i.e., pushbuttons, knobs, switches, etc.) to operate or control plant equipment with a touch-screen. Generally, a digital modification may consist of three common areas of activities: (1) software-related, (2) hardware-related and (3) Human-System Interface-related. NEI 96-07, Section 4.2.1.1 provides guidance for activities that involve "...an SSC design function..." or a "...method of performing or controlling a design function..." and Section 4.2.1.2 provides guidance for activities that involve "...how SSC design functions are performed or controlled (including changes to UFSAR-described procedures, assumed operator actions and response times)." Based on this segmentation of activities, the software and hardware portions will be assessed within the "facility" Screen consideration since these aspects involve SSCs or the method of performing or controlling a design function and the Human-System Interface portion will be assessed within the "procedures" Screen consideration since this portion involves how SSCs are operated and controlled.

4.2.1.1 Screening of Changes to the Facility as Described in the UFSAR SCOPE Many of the examples in this section involve the Main Feedwater (MFW) System to illustrate concepts. The reason for selecting the MFW system is NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-6 that it is one of the few non-safety-related systems that, upon failure, can initiate an accident. In the determination of potential adverse impacts, the following aspects should be addressed in the response to this Screen consideration: (a) Use of Software and Digital Devices (b) Combination of Components/Functions (c) Dependability Impact USE OF SOFTWARE AND DIGITAL DEVICES The UFSAR may identify SSC features design functions through diversity, separation, independence, defense-in-depth and/or redundancy discussions. With digital modifications, software and/or hardware have the potential to impact the diversity, separation, independence, defense-in-depth, and/or redundancy of SSCs identified explicitly and/

or implicitly described in the UFSAR.1 To assist in determining the impact of a digital modification on the diversity, separation, independence, defense-in-depth and/or redundancy of the affected SSCs described in the UFSAR, identify the features of the affected SSCs described in the UFSAR. Compare the proposed features of the affected SSCs with the existing features of the affected SSCs. The impact of any differences in the diversity, separation, independence, defense-in-depth and/or redundancy on the design functions described in the UFSAR of the affected SSCs is then determined. A digital modification that would reduce s SSC diversity, separation, independence, defense-in-dep th and/or redundancy is adverse. An adverse effect may also consist of the potential marginal increase in the likelihood of SSC failure due to the introduction of software. For redundant safety systems, this marginal increase in likelihood creates a similar marginal increase in the likelihood of a common failure in the redundant safety systems. On this basis, most digital modifications to redundant safety systems are adverse. However, for some digital modifications, engineering evaluations may show that the digital modification contains design attributes that meet NRC-endorsed acceptance criteria to eliminate consideration of a software common cause failure. In such cases, even when it affects a digital 1 Refer to NEI 96-07, Section 4.2.1.1, 2 nd paragraph.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-7 modification involves redundant systems, the digital modification would be not adverse. Alternately, the use of different software in two or more redundant SSCs is not adverse due to a software common cause failure because the there is no potential marginal mechanism to increase in the likelihood of failure due to the introduction of software. Examples 4-1a and 4-1b illustrate the application of the Use of Software and Digital Devices aspect. These examples illustrate how a variation in the licensing basis identified in the UFSAR can affect the Screen conclusion. Example 4-1a. NO ADVERSE IMPACT on a UFSAR-Described Design Function related to use of Software and Digital Devices Two non-safety-related main feedwater pumps (MFWPs) exist. There are two analog control systems (one per MFWP) that are physically and functionally the same.

The two analog control systems will be replaced with two digital control systems. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. The pertinent UFSAR SSC descriptions are as follows: (1) Two analog control systems are identified. (2) Both analog control systems consist of the same physical and functional characteristics. (3) The analog control system malfunctions include (a) failures causing the loss of all feedwater to the steam generators and (b) failures causing an increase in main feedwater flow to the maximum output from both MFWPs. The pertinent UFSAR-described design function of the main feedwater system is to automatically control and regulate feedwater to the steam generators. Use of the same hardware platforms and same software in both control systems is NOT ADVERSE for the following reasons: (a) Redundancy Consideration: There are is no impact on redundancy since the UFSAR does not describe redundant SSCs and there are no UFSAR-NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-8 described design functions related to redundancy. (b) Diversity Consideration: There are is no UFSAR SSC descriptions regarding diversity and impact on diversity since the UFSAR does not describe diverse SSCs and there are no UFSAR-described design functions related to diversity. (c) Separation Consideration: There is no impact on the separation of the control systems identified in the UFSAR since each of the analog control systems will be replaced with its own a separate digital control system. (d) Independence Consideration: Although both of the new digital control systems contain the exact same software (which is subject to a software CCFcommon cause failure), the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting the digital modification concluded that no new types of malfunctions are introduced since the loss of both MFWPs and failures causing an increase in main feedwater flow to the maximum output from both MFWPs are already considered in the licensing basis. (e) Defense-in-Depth Consideration: There are is no UFSAR SSC descriptions regarding defense-in-depth and impact on defense-in-depth since the UFSAR does not describe SSCs for the purpose of establishing defense-in-depth and there are no UFSAR-described design functions related to defense-in-depth. Through consideration of items (a) through (e) above, there is NO ADVERSE impact on the method of performing or controlling the design function of the main feedwater system to automatically control and regulate feedwater to the steam generators due to the use of software and digital devices. Example 4-1b. ADVERSE IMPACT on a UFSAR-Described Design Function related to use of Software and Digital Devices This example differs from Example 4-1a in only the types of malfunctions already identified in the UFSAR, as reflected in item (3) shown below. Items (1) and (2) are unaffected. (3) [Modified from Example 4-1a] The analog control system malfunctions include (a) failures causing the loss of feedwater from only one MWFP to the steam generators and (b) failures causing an increase in main feedwater flow to the maximum output from only one MFWP.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-9 The use of the same hardware platforms and same software in both control systems is ADVERSE due to its impact on the Independence Consideration. Items (a), (b), (c) and (e) are unaffected. (d) [Modified from Example 4-1a] Independence Consideration: Since the new digital control systems contain the exact same software (which is subject to a software CCFcommon cause failure), the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting the digital modification concluded that two new types of malfunctions are introduced since the loss of both MFWPs and failures causing an increase in main feedwater flow to the maximum output from both MFWP have been created and were not considered in the original licensing basis. There is an ADVERSE impact on the design function of the main feedwater system to automatically control and regulate feedwater to the steam generators due to the use of software that reduces independence and creates two new types of malfunctions. COMBINATION OF COMPONENTS/FUNCTIONS The UFSAR may identify the number of components, how the components were arranged, and/or how functions were allocated to those components. Any or all of these characteristics may have been considered in the process of identifying possible malfunctions or accident initiators. When replacing analog SSCs with digital SSCs, it is potentially advantageous to combine multiple compon ents and/or functions into a single device or control system. However, the failure of the single device or control system for any reason (e.g., a software common cause failure) can potentially affect multiple functions. The combination of previously separate components and/or functions, in and of itself, does not make the Screen conclusion adverse. Only if combining the previously separate components and/or functions causes a reduction in the SSC's ability or capability of performing a design function (e.g., by the creation of a new malfunction or the creation of a new malfunction or accident initiator) is the combination aspect of the digital modification adverse. To assist in determining the impact of a digital modification on the number and/or arrangement of components, review the description (s) of the existing NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-10 system(s) and/or component(s) SSCs described in the UFSAR. When comparing the existing and proposed configurations, consider how the proposed configuration affects the number and/or arrangement of components and the potential impacts of the proposed arrangement on UFSAR-described design functions. Examples 4-2 and 4-3 illustrate the application of the Combination of Components/Functions aspect. Examples 4-2a through and 4-2 cb illustrate how variations in a proposed activity and/or variations in the licensing basis identified in the UFSAR can affect the Screen conclusion. Example 4-2a. Combining Components and Functions with NO ADVERSE IMPACT on a UFSAR-Described Design Function Two non-safety-related main feedwater pumps (MFWPs) exist. There are two analog control systems (one per MFWP) that are physically and functionally the same. System drawings (incorporated by reference into the UFSAR) show that each analog control system has many subcomponents. All of the analog subcomponents will be replaced with a single digital device that consolidates all of the components, sub-components and the technical functions associated with each component and sub-component. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. The pertinent UFSAR SSC descriptions are as follows: (1) Two analog feedwater control systems are identified, including several major individual components. (2) The SSC descriptions state that both analog control systems consist of the same physical and functional characteristics. Although the control systems and the major components are described in the UFSAR, only a UFSAR-described design function for the feedwater control system is identified. No design functions for any of the individual components are described in the UFSAR. The pertinent UFSAR-described design function of the feedwater control system is "to provide adequate cooling water to the steam generators during normal operation." The UFSAR identifies the following MFWP control system malfunctions:

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-11 (a) failures causing the loss of all feedwater to the steam generators, and (b) failures causing an increase in main feedwater flow to the maximum output from both MFWPs. The combination of components and functions has NO ADVERSE IMPACT on the identified design function for the following reasons: No new malfunctions are created. The Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting the digital modification concluded that no new types of malfunctions are introduced since the loss of both MFWPs and failures causing an increase in main feedwater flow to the maximum output from both MFWPs are already considered in the licensing basis. Since no new malfunctions are created, the ability to perform the design function "to provide adequate cooling water to the steam generators during normal operation" is maintained. Using the same initial SSC configuration, proposed activity and UFSAR descriptions from Example 4-2a, Example 4-2b illustrates how a variation in the proposed activity would be addressed. Example 4-2b. Combining Components and Functions with NOan ADVERSE IMPACT on a UFSAR-Described Design Function Instead of two separate, discreet, unconnected digital control systems being used for the feedwater control systems, only one central digital processor is proposed to be used that will combine the previously separate control systems and control both feedwater pumps. Although the UFSAR explicitly identifies the existence of two control systems, combining the two analog control systems into one digital control system is NOT adverse due to the combination aspect because no new malfunctions are created (i.e., the loss of both control systems and the maximum feedwater flow from both feedwater pumps have been previously considered in the licensing basis). Since no new malfunctions are created, the ability of the design function "to provide adequate cooling water to the steam generators during normal operation" is maintained.In this case, the proposed activity is ADVERSE because there is a reduction in the separation of the two original control systems.

Using the same initial SSC configuration and proposed activity from Example 4-2a, Example 4-2c illustrates how a variation in the licensing basis identified in the UFSAR impacts the Screen conclusion, causing an adverse impact.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-12 Example 4-2c. Combining Components and Functions with an ADVERSE IMPACT on a UFSAR-Described Design Function Instead of the loss of all feedwater to the steam generators due to the loss of both analog control systems being previously considered in the licensing basis, the loss of only one analog control system (and its worst-case affect on feedwater flow) has been considered. In this case, the proposed activity would be adverse since a new malfunction is created (i.e., loss of both control systems) due to a software common cause failure and the reduction in the ability of the design function "to provide adequate cooling water to the steam generators during normal operation." Example 4-3 illustrates the combining of control systems from different, originally separate systems. Example 4-3. Combining Components and Functions with an ADVERSE IMPACT on a UFSAR-Described Design Function Two non-safety-related analog feedwater control systems and a separate analog control system that controls the main turbine steam-inlet valves exist.All three analog control systems will be replaced with one digital control system that will combine the two feedwater control systems and the main turbine steam-inlet valve control system into a single digital device. The pertinent UFSAR SSC descriptions are as follows: (1) Two analog feedwater control systems are identified. The feedwater control system contains a design function "to provide adequate cooling water to the steam generators during normal operation." (2) One analog main turbine steam-inlet valve control system is identified. The main turbine steam-inlet valve control system contains a design function "to control the amount of steam entering the main turbine during normal operation." (3) The two feedwater control systems are independent from the main turbine steam-inlet valve control system. (4) The function of controlling feedwater is separate from the function of controlling the main turbine steam-inlet valves. This separation is confirmed by a review of the accident analyses that do not include consideration of a simultaneous failure of the feedwater control system and the failure of the NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-13 turbine control system. The proposed activity is adverse because combining the previously separate components and functions causes a reduction in each of the control system's ability to separately perform their design functions.In this case, the proposed activity is ADVERSE because there is a reduction in the separation and independence of the original control systems. DEPENDABILITY IMPACT In the main body of NEI 96-07, Section 4.2.1, subsection titled "Screening for Adverse Effects," reliability is mentioned in the following excerpt:

"...a change that decreases the reliability of a function whose failure could initiate an accident would be considered to adversely affect a design function..." Based on the technical outcomes from NRC-approved and NRC-endorsed sources applicable Industry and/or NRC guidance documents and using the information considered in those sources to develop those outcomes, the Screen should assess the dependability of performing applicable design functions due to the introduction of software and/or hardware. Example 4-4 illustrates the application of the dependability consideration. Example 4-4. Digital Modification that Satisfies Dependability, causing NO ADVERSE IMPACT on a UFSAR-described Design Function An analog recorder is to be replaced with a new microprocessor-based recorder. The recorder is used for various purposes including Post Accident Monitoring, which is a UFSAR-described design function. Dependability Assessment: An engineering evaluation performed as part of the technical assessment supporting the digital modification concluded that the new recorder will be highly dependable (based on a quality development process, testability, and successful operating history) and therefore, the risk of failure of the recorder due to software is considered very low. The change will have NO ADVERSE IMPACT on any design function due to the dependability assessment.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-14 4.2.1.2 Screening of Changes to Procedures as Described in the UFSAR SCOPE In NEI 96-07, Section 3.11 defines procedures as follows:

"...Procedures include UFSAR descriptions of how actions related to system operation are to be performed and controls over the performance of design functions. This includes UFSAR descriptions of operator action sequencing or response times, certain descriptions...of SSC operation and operating modes, operational...controls, and similar information." Because the Human-System Interface involves system/component operation, operator actions, response times, etc., this portion of a digital modification is assessed in this Screen consideration. If the digital modification does not include or affect a Human-System Interface (e.g., the replacement of a stand-alone analog relay with a digital relay that has no features involving personnel interaction and does not feed signals into any other analog or digital device), then this section does not apply and may be excluded from the Screen assessment. The focus of the Screen assessment is on potential adverse effects due to modifications of the interface between the human user and the technical device [e.g., equipment manipulations, actions taken, options available, decision-making, manipulation sequences or operator response times (including the impact of errors of a cognitive nature in which the information being provided is unclear or incorrect)], not the written procedure modifications that may accompany a physical design modification (which are addressed in the guidance provided in NEI 96-07, Section 4.2.1.2). PHYSICAL INTERFACE WITH THE HUMAN-SYSTEM INTERFACE In the determination of potential adverse impacts, the following aspects should be addressed in the response to this Screen consideration: (a) Physical Interaction with the Human-System Interface (HSI) (b) Number/Type of Parameters (c) Information Presentation (d) Operator Response Time NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-15 Physical Interaction with the Human-System Interface A typical physical interaction modification might involve the use of a touch screen in place of push-b uttons, switches or knobs, including sensory-based aspects such as auditory or tactile feedback. To determine if the HSI aspects of a digital modification have an adverse impact on UFSAR-described design functions, potential impacts due to the physical interaction with the HSI should be addressed in the Screen. Consideration of a digital modificati on's impact due to the physical interaction with the HSI involves an examination of the actual physical interface and how it could impact the performance and/or satisfaction of UFSAR-described design functions. For example, if a new malfunction is created as a result of the physical interaction, then the HSI portion of the digital modification would be adverse. Such a new malfunction may be created by the interface requiring the human user to choose which of multiple components is to be controlled, creating the possibility of selecting the wrong component (which could not occur with an analog system that did not need the human user to "make a selection").

Characteristics of HSI changes that could lead to potential adverse effects may include, but are not limited to:

  • Changes from manual to automatic initiation (or vice versa) of functions,
  • Changes in the data acquisition process (such as replacing an edgewise analog meter with a numeric display or a multipurpose CRT in which access to the data requires operator interaction to display), or
  • Changes that create new potential failure modes in the interaction of operators with the system (e.g., new interrelationships or interdependencies of operator actions and/or plant response, or new ways the operator assimilates plant status information),
  • Increased possibility of mis-operation related to performing a design function,
  • Increased difficulty for an operator to perform a design function, or
  • Increased complexity or duration in diagnosing or responding to an accident [e.g., Time-Critical Operation Actions (TCOAs) identified in the UFSAR]. If the HSI changes do not exhibit characteristics such as those listed above, then it may be reasonable to conclude that the "method of performing or controlling" a design function is not adversely affected.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-16 Examples 4-5 through 4-7 illustrate the application of the Physical Interaction aspect. Example 4-5. Physical Interaction with NO ADVERSE IMPACT on a UFSAR-Described Design Function Currently, a knob is rotated clock-wise to increase a control function and counter clock-wise to decrease the control function. This knob will be replaced with a touch screen. Using the touch screen, touching the "up" arrow will increase the control function and touching the "down" arrow will decrease the control function. The UFSAR-described design function states the operator can "increase and decrease the control functions using manual controls located in the Main Control Room." Thus, this UFSAR description indirectly implicitly identifies the SSC (i.e., the knob) and the design function of the SSC (i.e., its ability to allow the operator to manually adjust the control function). As part of the technical evaluation supporting the proposed activity, a Human Factors Evaluation (HFE) was performed. The HFE concluded that no new failures or malfunctions have been introduced as a result of the replacement from a knob to a touch screen. Using the results from the HFE and examining only the physical interaction aspect (e.g., ignoring the impact on operator response time or the number and/or sequence of steps necessary to access the new digital controls), the replacement of the "knob" with a "touch screen" is not adverse since it does not impact the ability of the operator to "increase and decrease the control functions using manual controls located in the Main Control Room," maintaining satisfaction of the UFSAR-described design function.

Using the same proposed activity provided in Example 4-5, Example 4-6 illustrates how a variation in the UFSAR description would cause an adverse impact. Example 4-6. Physical Interaction with an ADVERSE IMPACT on a UFSAR-Described Design Function The UFSAR states not only that the operator can "increase and decrease the control functions using manual controls located in the Main Control Room," but also that "the control mechanism provides tactile feedback to the operator as the mechanism is rotated through each setting increment." Since a touch screen cannot provide (or duplicate) the "tactile feedback" of a mechanical device, replacing the "knob" with a "touch screen" is adverse NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-17 because it adversely impacts the ability of the operatorto obtain tactile feedback from the device.

Using the same proposed activity provided in Example 4-5 and the same UFSAR descriptions from Example 4-6, Example 4-7 illustrates how a variation in the proposed activity would also cause an adverse impact. Example 4-7. Physical Interaction with an ADVERSE IMPACT on a UFSAR-Described Design Function In addition to the touch screen control "arrows" themselves, a sound feature and associated components will be added to the digital design that will emit a clearly audible and distinct "tone" each time the control setting passes through the same setting increment that the tactile feature provided with the mechanical device. Although the operator will now receiv e auditory "feed back" during the operation of the digital device, the means by which this feedback is provided has been altered. Since the means of controlling the design function has changed, new malfunctions can be postulated (e.g., high ambient sound levels that prevent the operator from hearing the feedback). Therefore, the modification of the feedback feature (i.e., from tactile to auditory) has an adverse impact on the ability of the design function to be performed.

Number and/or Type of Parameters Displayed By and/or Available From the Human-System Interface One advantage of a digital system is the amount of information that can be monitored, stored and presented to the user. However, the possibility exists that the amount of such information may lead to an over-abundance that is not necessarily beneficial in all cases. To determine if the HSI aspects of a digital modification have an adverse effect on UFSAR-described design functions, potential impacts due to the number and/or type of parameters displayed by and/or available from the HSI should be addressed in the Screen. Consideration of a digital modification's impact due to the number and/or type of parameters displayed by and/or available from the HSI involves an examination of the actual number and/or type of parameters displayed by and/or available from the HSI and how they could impact the performance and/or satisfaction of UFSAR-described design functions. Potential causes for an adverse impact on a UFSAR-described design function could include a reduction in the number of parameters monitored (which could make the NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-18 diagnosis of a problem or determination of the proper action more challenging or time-consuming for the operator), the absence of a previously available parameter (i.e., a type of parameter), a difference in how the loss or failure of parameters occurs (e.g., as the result of combining parameters), or an increase in the amount of information th at is provided such that the amount of available information has a detrimental impact on the operator's ability to discern a particular plant condition or to perform a specific task. Example 4-8 illustrates the application of the Number and/or Type of Parameters aspect. Example 4-8. Number and Type of Parameters with NO ADVERSE IMPACT on a UFSAR-Described Design Function Currently, all controls and indications for a single safety-related pump are analog. There are two redundant channels of indications, either of which can be used to monitor pump performance, but only one control device. For direct monitoring of pump performance, redundant motor electrical current indicators exist. For indirect monitoring of pump performance, redundant discharge pressure and flow rate indicators exist. Furthermore, at the destination of the pump's flow, redundant temperature indicators exist to allow indirect monitoring of pump performance to validate proper pump operation by determination of an increasing temperature trend (i.e., indicating insufficient flow) or a stable/decreasing temperature trend (i.e., indicating sufficient flow). All of these features are described in the UFSAR. The UFSAR also states that the operator will "examine pump performance and utilize the information from at least one of the redundant plant channels to verify performance" and "the information necessary to perform this task is one parameter directly associated with the pump (motor electrical current) and three parameters indirectly as sociated with pump performance (discharge pressure, flow rate, and response of redundant temperature indications)." A digital system will replace all of the analog controls and indicators. Two monitoring stations will be provided, either of which can be used to monitor the pump. Each monitoring station will display the information from one of the two redundant channels. The new digital system does not contain features to automatically control the pump, but does contain the ability to monitor each of the performance indications and inform/alert the operator of the need to take action. Therefore, all pump manipulations will still be manually controlled. Since the new digital system presents the same number (one) and type (motor electrical current) of pump parameters to directly ascertain pump NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-19 performance and the same number (three) and type (discharge pressure, flow rate and redundant temperature) of system parameters to indirectly ascertain pump performance, there is no adverse impact on the UFSAR-described design function to perform direct monitoring of pump performance and no adverse impact on the UFSAR-described design function to perform indirect monitoring of pump performance.

Information Presentation on the Human-System Interface A typical change in data presentation might result from the replacement of an edgewise analog meter with a numeric display or a multipurpose CRT. To determine if the HSI aspects of a digital modification have an adverse effect on UFSAR-described design functions, potential impacts due to how the information is presented should be addressed in the Screen. Consideration of a digital modification's impact due to how the information is presented involves an examination of how the actual information presentation method could impact the performance and/or satisfaction of UFSAR-described design functions. To determine possible impacts, the UFSAR should be reviewed to identify descriptions regarding how information is presented, organized (e.g., how the information is physically presented) or accessed, and if that presentation, organization or access relates to the performance and/or satisfaction of a UFSAR-described design function. Examples of activities that have the potential to cause an adverse effect include the following activities:

  • Addition or removal of a dead-band, or
  • Replacement of instantaneous readings with time-averaged readings (or vice-versa). If the HSI changes do not exhibit characteristics such as those listed above, then it may be reasonable to conclude that the "method of performing or controlling" a design function is not adversely affected. Example 4-9 illustrates the application of the Information Presentation aspect. Example 4-9. Information Presentation with an ADVERSE IMPACT on a UFSAR-Described Design Function A digital modification consolidates system information onto two flat panel displays (one for each redundant channel/train). Also, due to the increased NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-20 precision of the digital equipment, the increment of presentation on the HSI will be improved from 10 gpm to 1 gpm. Furthermore, the HSI will now present the information layout "by channel/train." The UFSAR identifies the existing presentation method as consisting of "indicators with a 10 gpm increment" to satisfy safety analysis assumptions and the physical layout as being "by flow path" to allow the operator to determine system performance.

The increase in the display increment is not adverse since the operator will continue to be able to distinguish the minimum increment of 10 gpm UFSAR-described design function. The new display method (i.e., "by channel/train") adversely affects the ability of the operator to satisfy the design function to ascertain system performance "by flow path." Operator Response Time

Typically, an increase in the operator response time might result from the need for the operator to perform additional actions (e.g., due to the additional steps necessary to call up or retrieve the appropriate display and operate the "soft" control rather than merely reading an indicator on the Main Control Board). To determine if the HSI aspects of a digital modification have an adverse effect on UFSAR-described design functions, potential impacts on the operator response time should be addressed in the Screen. Consideration of a digital modification's impact on the operator response time due to the modification of the number and/or type of decisions made, and/or the modification of the number and/or type of actions taken, involves an examination of the actual decisions made/actions taken and how they could impact the performance and/or satisfaction of UFSAR-described design functions. To determine possible impacts, the UFSAR must be reviewed to identify descriptions relating to operator response time requirements and if those timing requirements are related to the performance and/or satisfaction of a UFSAR-described design function. Example 4-10 is the same as Example 4-9, but illustrates the application of the Operator Response Time aspect. Example 4-10. Operator Response Time with NO ADVERSE IMPACT on a UFSAR-Described Design Function NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-21 A digital modification consolidates system information onto two flat panel displays (one for each redundant channel/train). Also, due to the increased precision of the digital equipment, the increment of presentation on the HSI will be improved from 10 gpm to 1 gpm. Furthermore, the HSI will now present the information layout "by channel/train." The UFSAR identifies the existing presentation method as consisting of the physical layout as being "by flow path" to allow the operator to determine system performance.

Although the UFSAR identifies the existing presentation method as consisting of a physical layout as being "by flow path" to allow the operator to determine system performance and the new display method (i.e., "by channel/train") will require additional steps by the operator to determine system performance, requiring more time, there is no adverse impact on satisfaction of the design function to ascertain sy stem performance because no response time requirements are applicable to the design function of the operator being able "to determine system performance.

COMPREHEHSIVE COMPREHENSIVE HUMAN-SYSTEM INTERFACE EXAMPLE Although no additional guidance is provided in this section, Example 4-11 illustrates how each of the aspects identified above would be addressed. Example 4-11. Digital Modification involving Extensive HSI Considerations with NO ADVERSE IMPACTS on a UFSAR-Described Design Function Component controls for a redundant safety-related system are to be replaced with PLCs. The existing HSI for these components is made up of redundant hard-wired switches, indicator lights, and analog meters. The new system consolidates the information and controls onto two flat panel displays (one per redundant train), each with a touch screen providing "soft" control capability. The existing number and type of parameters remains the same, which can be displayed in a manner similar to the existing presentations (e.g., by train). However, the information can be also presented in different configurations that did not previously exist (e.g., by path or by parameter type to allow for easier comparison of like parameters), using several selectable displays. The flat panel display can also present any of several selectable pages depending on the activity being performed by the operator (e.g., Formatted: Keep with next NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-22 starting/initiating the system, monitoring the system during operation, orchanging the system line-up). To operate a control, the operator mu st (via the touch screen) select the appropriate activity (e.g., starting/initiating the system, monitoring the system during operation, or changing the system line-up), select the desired page (e.g., train presentation, path presentation, or parameter comparison), select the component to be controlled (e.g., pump or valve), select the control action (e.g., start/stop or open/close), and execute it. The display remains on the last page selected, but each page contains a "menu" of each possible option to allow direct access to any page without having to return to the "main menu." The two new HSIs (one per redundant train) will provide better support of operator tasks and reduced risk of errors due to:

  • Consolidation of needed information onto a single display (within the family of available displays) that provides a much more effective view of system operation when it is called into action.
  • Elimination of the need for the operator to seek out meter readings or indications, saving time and minimizing errors.
  • Integration of cautions and warnings within the displays to help detect and prevent potential errors in operation (e.g., warnings about incorrect system lineups during a test or maintenance activity). The design was developed using a human factors engineering design, with a verification and validation process consistent with current industry and regulatory standards and guidelines. As part of the technical evaluation supporting the proposed activity, a Human Factors Evaluation (HFE) was performed. Based on the conclusions from the HFE, the design provides a more effective HSI that is less prone to human error than the existing design. The UFSAR-described design functions a pplicable to this proposed activity include descriptions of the existing controls, including the physical switches, indicator lights and meters, and how each of these SSCs is used during normal and abnormal (including accident) operating conditions. The UFSAR identifies the current physical arrangement (i.e., two physically separate locations) as providing a design functi on that prevents the operator from operating the "wrong" component. There are no UFSAR-described design functions related to the operator response times associated with using the existing controls. The impacts on design functions are identified below:

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-23

  • Physical Interaction - NOT ADVERSE because the new HSI consists of two physically separate displays.
  • Number and Type of Parameters - NOT ADVERSE because the same number and type of parameters exist with the new HSI.
  • Information Presentation - NOT ADVERSE because all of the existing features (e.g., individual controls, indicator lights and parameters displays that mimic the analog meters) continue to exist with the new HSI.
  • Operator Response Time - NOT ADVERSE because no response time requirements were applicable to any of the design functions.

4.2.1.3 Screening Changes to UFSAR Methods of Evaluation By definition, a proposed activity involving a digital modification involves SSCs and how SSCs are operated and controlled, not a method of evaluation described in the UFSAR (see NEI 96-07, Section 3.10). Methods of evaluation are analytical or numerical computer models used to determine and/or justify conclusions in the UFSAR (e.g., accident analyses that demonstrate the ability to safely shut down the reactor or prevent/limit radiological releases). These models also use "software." However, the software used in these models is separate and distinct from the software installed in the facility. The response to this Screen consideration should reflect this distinction. A necessary revision or replacement of a method of evaluation (see NEI 96-07, Section 3.10) resulting from a digital modification is separate from the digital modification itself and the gu idance in NEI 96-07, Section 4.2.1.3 applies. 4.2.2 Is the Activity a Test or Experiment Not Described in the UFSAR? By definition, a proposed activity involving a digital modification involves SSCs and how SSCs are operated and controlled, not a test or experiment (see NEI 96-07, Section 4.2.2). The response to this Screen consideration should reflect this characterization. A necessary test or experiment (see NEI 96-07, Section 3.14) involving a digital modification is separate from the digital modification itself and the guidance in NEI 96-07, Section 4.2.2 applies.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-24 4.3 E VALUATION PROCESS

In the following sections and sub-sections that describe the Evaluation guidance unique to the application of 10 CFR 50.59 to digital modifications, each section and sub-section describes only a specific aspect, sometimes at the deliberate exclusion of other related aspects. This focused approach is intended to concentrate on the particular aspect of interest and does not imply that the other aspects do not apply or could not be related to the aspect being addressed. Throughout this section, references to the main body of NEI 96-07, Rev. 1 will be identified as "NEI 96-07." Common Cause Failure (CCF) Outcomes The possible outcomes regarding a CCF from the CCF Susceptibility Analysis performed in accordance with applicable NRC-approved and/or NRC-endorsed sources Industry and/or NRC guidance documents are as follows: (1) CCF not credible (i.e., likelihood of a CCF caused by an I&C failure source is NOT greater than the likelihood of a CCF caused by other failure sources that are not considered in the UFSAR)

(2) CCF credible (i.e., likelihood of a CCF caused by an I&C failure source IS greater than or equal to the likelihood of a CCF caused by other failure sources that are considered in the UFSAR)

(a) CCF Likelihood much lower than Single Random Hardware Failure Likelihood (b) CCF Likelihood NOT much lower than Single Random Hardware Failure Likelihood These outcomes will be used in developing the responses to Evaluation criteria 1, 2, 5 and 6.

CAUTION The guidance contained in this appendix is intended to supplement the generic Evaluation guidance contained in the main body in NEI 96-07, Section 4.3. Namely, the generic Evaluation guidance provided in the main body of NEI 96-07 and the more-focused Evaluation guidance in this appendix BOTH apply to digital modifications.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-25 Examples Examples are provided to illustrate the guidance provided herein. Unless stated otherwise, a given example only addresses the aspect or topic within the section/sub-section in which it is included, sometimes at the deliberate exclusion of other aspects or topics that, if considered, could potentially change the Evaluation conclusion. Many of the examples in this section involve the Main Feedwater (MFW) System to illustrate concepts. The reason for selecting the MFW system is that it is one of the few non-safety-related systems that, upon failure, can initiate an accident. Furthermore, a failure of the MFW system is one of the few malfunctions that are also accident initiators. 4.3.1 Does the Activity Result in More Than a Minimal Increase in the Frequency of Occurrence of an Accident? INTRODUCTION From NEI 96-07, Section 3.2:

"The term 'accidents' refers to the anticipated (or abnormal) operational transients and postulated design basis accidents..." Therefore, for purposes of 10 CFR 50.59, both Anticipated Operational Occurrences (AOOs) and Postulated Accidents (PAs) fall within the definition of "accident." After applying the generic guidance in NEI 96-07, Section 4.3.1 to identify any accidents affected by the systems/components involved with the digital modification and examining the initiators of those accidents, the impact on the frequency of the initiator (and, hence, the accident itself) due to the digital modification can be assessed. All accident initiators fall into one of two categories: equipment-related or personnel-related. Therefore, the assessment of the impact of a digital modification also needs to consider both equipment-related and personnel-related sources. For a digital modification, the range of possible equipment-related sources includes items unique to digital and items not unique to digital. An example of an item unique to digital is cons ideration of the impact on accident frequency due to a CCF, which will be addressed in the guidance in this section. An example of an item not unique to digital is consideration of the impact on accident frequency due to the digital system's compatibility with NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-26 the environment in which the system is being installed, which would be addressed by applying the guidance described in NEI 96-07, Section 4.3.1. For a digital modification, the assessment for personnel-related sources will consider the impact due to the Human-System Interface (HSI). Typically, numerical values quantifying an accident frequency are not available, so the qualitative approach using the attributable and the magnitude (i.e., negligible/discernable) criteria from NEI 96-07, Section 4.3.1 will be examined in the guidance in this section.

GUIDANCE Factors to Consider and Address in the Response 1. Use of Software Software developed in accordance with a defined life cycle process, and complies with applicable industry standards and regulatory guidance does not result in more than a minimal increase in the frequency of an accident. The design change process and the design documentation contain the information that will be used to determine if software increases the frequency of an accident. 2. Use of Digital Components (e.g., microprocessors in place of mechanical devices) NOTE: This factor is not unique to digital and would be addressed by applying the guidance described in NEI 96-07, Section 4.3.1. This factor is included here for completeness. Digital components are expected to be more reliable than the equipment being replaced. Aspects to be addressed include the following: compliance with applicable regulations and industry standards; qualification for environmental conditions (seismic, temperature, humidity, radiation, pressure, and EMCelectromagnetic compatibilityinterference); performance requirements for the plant-specific application; proper design of electrical power supplies; cooling or ventilation for thermal loads; and separation, independence and grounding. The design change process and the design documentation contain the information that will be used to determine if the use of digital components increases the frequency of an accident. 3. Creation of a Software Common Cause Failure NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-27 An engineering evaluation of the quality and design processes determines the likelihood of failure due to software via a common cause failure and its potential impact on the frequency of an accident. As stated above, tT his information is documented in the qualitative assessment of the potential contributors to CCF and disposition of whether the design effectively reduced the likelihood of the CCF to the extent that the CCF can be considered not credible (e.g., in a CCF Susceptibility Analysis

). 4. Intended Benefits of the Digital Component/System NOTE: This factor is not unique to digital and would be addressed by applying the guidance described in NEI 96-07, Section 4.3.1. This factor is included here for completeness. In addition to the expected hardware-related reliability improvements of the physical devices themselves (addressed in factor 2 above), overall improvements in the reliability of the performance of the digital component/system, operational flexibility and/or maintenance-related activities may also be achieved. The design documentation contains the information that will be used to identify the intended benefits of the digital component/system and possible impacts on the frequency of an accident.

5. Design Attributes/Features Design attributes of the proposed digital modification are features that serve to prevent or limit failures from occurring, or that mitigate the results/outcomes of such possible failures. Factors to be considered include the following items:
  • Design Criteria (as applicable) (e.g., diversity, independence and redundancy)
  • Inherent Design Features for Software, Hardware or the Architectural/Network (e.g., external watchdog timers, isolation devices, segmentation, self-testing and self-diagnostic features)
  • Non-concurrent Triggers
  • Sufficiently Simple (i.e., enabling comprehensive testing)
  • Unlikely Series of Events (e.g., the evaluation of a given digital modification would need to postulate multiple independent random failures in order to arrive at a state in which a SCCF is possible)
  • Failure State (e.g., always known to be acceptable)

Determination of Attributable If a CCF is determined to be not credible, then there is NO attributable impact on the frequency of occurrence of an accident. Namely, if a CCF does Formatted: Keep with next NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-28 not is sufficiently unlikely to occur, then no mechanism for an attributable impact has been created. If a CCF is determined to be credible, but the component/system is not an accident initiator, then there is NO attributable impact on the frequency of occurrence of an accident. Namely, even if a CCF does occur, there is no relationship between the CCF and the accident initiator(s). Example 4-12 illustrates the case of NO attributable impact on the frequency of occurrence of an accident for a SSC not being an accident initiator. Example 4-12. NO ATTRIBUTABLE Impact on the Frequency of Occurrence of an Accident Due to a SSC Not Being an Accident Initiator Proposed Activity Two safety-related containment chillers exist. There are two analog control systems (one per chiller) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Affected Accidents and Accident Initiators The review of the UFSAR accident analyses identified the Loss of Coolant Accident (LOCA) and Main Steam Line Break (MSLB) events as containing requirements related to the safety-related containment chillers. Specifically, the UFSAR states the following: "To satisfy single failure requirements, the loss of only one control system and its worst-case effect on the containment post-accident environment due to the loss of one chiller has been considered in the LOCA and MSLB analyses." Therefore, the affected accidents are LOCA and MSLB. The UFSAR identified an equipment-related initiator in both cases as being a pipe break. For LOCA, the pipe break occurs in a hot leg or a cold leg. For MSLB, the pipe break occurs in the main steam line exiting the steam generator. Impact on Accident Frequency In this case, the safety-related containment chillers are not related to the accident initiators (i.e., pipe breaks). Furthermore, the chillers are only considered as part of accident mitigation; after the accidents have already NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-29 occurred. Therefore, there is NO impact on the frequency of occurrence of the accidents that can be attributed to the digital modification. If a CCF is determined to be credible and the component/system is an accident initiator, then there is an attributable potential impact on the frequency of occurrence of the accident. Example 4-13 illustrates the case of an attributable potential impact on the frequency of occurrence of an accident for the SSC being an accident initiator. Example 4-13. ATTRIBUTABLE Potential Impact on the Frequency of Occurrence of an Accident Due to a SSC Being an Accident Initiator Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Affected Accident and Accident Initiators The affected accident is the Loss of Feedwater event. The UFSAR identifies the equipment-related initiators as being the loss of one MFWP or the closure of one MFWP flow control valve. Impact on Accident Frequency Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF causing the loss of both feedwater control systems (resulting in the loss of both MWFPs and/or the closure of both MFWP flow control valves) has been determined to be credible. Since the failure of the digital feedwater control systems can cause the loss of MFWPs or the closure of MFWP flow control valves, a potential impact on accident frequency due to the CCF can be attributed to the digital modification.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-30 Determination of Magnitude (using Negligible/Discernable) For the case in which a CCF is credible and there is an attributable potential impact on the frequency of occurrence of an accident, the magnitude portion of the criteria (i.e., negligible/discernable) also needs to be assessed. To determine the overall effect of the digital modification on the frequency of an accident, examination of all the factors associated with the digital modification and their interdependent relationship need to be considered. To achieve a negligible conclusion, the examinatio n of all the factors would conclude that the net change in the accident frequency "...is so small or the uncertainties in determining whether a change in frequency has occurred are such that it cannot be reasonably concluded that the frequency has actually changed (i.e., there is no clear trend toward increasing the frequency)" [emphasis added] due to the net effect s of the factors considered (i.e., use of software ("positive"), improved hardware reliability ("positive") use of digital components, creation of a software CCF ("negative") and the , intended benefits ("positive")and design attributes/features). Alternately, if the net effects are such that a clear trend towards increasing the frequency would result, a discernable increase in the accident frequency would exist. However, to remain consistent with the guidance provided in NEI 96-07, Section 4.3.1, a discernable increase in the accident frequency would NOT be more than minimal if applicable NRC requirements, as well as design, material, and construction standards, continue to be met. Examples 4-14 and 4-15 will examine the magnitude portion (i.e., negligible/discernable) of the criteria and assume the attributable portion of the criteria has been satisfied. Example 4-14 illustrates the NEGLIGIBLE impact case. Example 4-14. NEGLIGIBLE Impact on the Frequency of Occurrence of an Accident Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-31 system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Attributable Conclusion See Example 4-13. Magnitude Conclusion Factors Considered: 1. Software - Developed in accordance with a defined life cycle process, and complies with applicable industry standards and regulatory guidance 2. Digital Components - More reliable, comply with all applicable standards, and meet all applicable technical requirements 3. CCF - Not Credible, but the CCF likelihood is much lower than the single random hardware failure likelihood

4. Benefits - Reliability and performance increased
5. Design Attributes/Features - [LATER] Based on the factors considered, tThe net change in the frequency of occurrence of the Loss of Feedwater event is negligible due to the interdependent effects of CCF ("negative") and use of software, use of digital devices and improved SSC performance ("positive")net effect of the factors considered. Overall Conclusion Although an attributable potential impact on the frequenc y of occurrence of the Loss of Feedwater event was determined to exist, there was no clear trend toward increasing the frequency. With no clear trend toward increasing the frequency, there is not more than a minimal increase in the frequency of occurrence of the accident due to the digital modification. Example 4-15 illustrates the DISCERNABLE increase case. Example 4-15. DISCERNABLE Increase in the Frequency of Occurrence of an Accident NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-32 Proposed Activity Same as Example 4-14. Attributable Conclusion See Example 4-13. Magnitude Conclusion Factors Considered: 1. Software - Same as Example 4-14. 2. Digital Components - Same as Example 4-14. 3. CCF - Credible, with the CCF likelihood NOT much lower than the single random hardware failure likelihood
4. Benefits - Same as Example 4-14.
5. Design Attributes/Features - Same as Example 4-14 Requirements/Standards Consideration All applicable NRC requirements, as well as design, material and construction standards, continue to be met. Based on the factors considered, tThe net change in the frequency of occurrence of the Loss of Feedwater event is discernable due to the net effect of the CCF ("negative") and the use of software, use of digital devices and improved SSC performance ("positives")factors considered. Overall Conclusion An attributable potential impact on the frequency of occurrence of the Loss of Feedwater event was determined to exist and there is a clear trend towards increasing the frequency. The clear trend toward increasing the frequency (i.e., the discernable increase) is due to the CCF likelihood NOT being much lower than the single random hardware failure likelihood, which does not satisfy the NRC requirements associated with systems/components that must satisfy single failure requirements being credible. With However, even with a Formatted: Keep with next NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-33 clear trend towards increasing the frequency,and the failure to satisfy an NRC requirement, satisfaction of all applicable NRC requirements, as well as design, material and construction standards, means that there is NOT more than a minimal increase in the frequency of occurrence of the accident due to the digital modification.

HUMAN-SYSTEM INTERFACE ASSESSMENT If no personnel-based initiators (e.g., operator error) are identified among the accident initiators, then an increase in the frequency of th e accident cannot occur due to the Human-System Interface portion of the digital modification. If personnel-based initiators (e.g., operator error) are identified among the accident initiators, then the application of the attributable criterion and the magnitude criterion (i.e., negligible/discernable) are assessed utilizing the guidance described in NEI 96-07, Section 4.3.1. 4.3.2 Does the Activity Result in More Than a Minimal Increase in the Likelihood of Occurrence of a Malfunction of an SSC Important to Safety? INTRODUCTION After applying the generic guidance in NEI 96-07, Section 4.3.2 to identify any malfunctions affected by the systems/components in volved with the digital modification and examining the initiators of those malfunctions, the impact on the likelihood of the initiator (and, hence, the malfunction itself) due to the digital modification can be assessed. All malfunction initiators fall into one of two categories: equipment-related or personnel-related. Th erefore, the assessment of the impact of a digital modification also needs to consider both equipment-related and personnel-related sources. For a digital modification, the range of possible equipment-related sources includes items unique to digital and items not unique to digital. An example of an item unique to digital is consideration of the impact on malfunction likelihood due to a CCF, which will be addressed in the guidance in this section. An example of an item not unique to digital is consideration of the impact on malfunction likelihood due to the digital system's compatibility with the environment in which the system is being installed, which would be addressed by applying the guidance described in NEI 96-07, Section 4.3.2.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-34 For a digital modification, the assessment for personnel-related sources will consider the impact due to the Human-System Interface (HSI). Typically, numerical values quantify ing a malfunction likelihood are not available, so the qualitative approach using the attributable and the magnitude (i.e., negligible/discernable) criteria from NEI 96-07, Section 4.3.2 will be examined in the guidance in this section.

GUIDANCE Factors to Consider and Address in the Response 1. Use of Software Software developed in accordance with a defined life cycle process, and complies with applicable industry standards and regulatory guidance does not result in more than a minimal increase in the likelihood of a malfunction. The design change process and the design documentation contain the information that will be used to determine if software increases the likelihood of a malfunction. 2. Use of Digital Components (e.g., microprocessors in place of mechanical devices) NOTE: This factor is not unique to digital and would be addressed by applying the guidance described in NEI 96-07, Section 4.3.2. This factor is included here for completeness. Digital components are expected to be more reliable than the equipment being replaced. Aspects to be addressed include the following: compliance with applicable regulations and industry standards; qualification for environmental conditions (seismic, temperature, humidity, radiation, pressure, and EMCelectromagnetic interferencecompatibility); performance requirements for the plant-specific application; proper design of electrical power supplies; cooling or ventilation for thermal loads; and separation, independence and grounding. The design change process and the design documentation contain the information that will be used to determine if the use of digital components increases the likelihood of a malfunction. 3. Creation of a Software Common Cause Failure An engineering evaluation of the quality and design processes determines the likelihood of failure due to software via a common cause failure and its potential impact on the likelihood of a malfunction. As stated above, tThis NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-35 information is documented in the qualitative assessment of the potential contributors to CCF and disposition of whether the design effectively reduced the likelihood of the CCF to the extent that the CCF can be considered not credible (e.g., in a CCF Susceptibility Analysis

). 4. Intended Benefits of the Digital Component/System NOTE: This factor is not unique to digital and would be addressed by applying the guidance described in NEI 96-07, Section 4.3.2. This factor is included here for completeness. In addition to the expected hardware-related reliability improvements of the physical devices themselves (addressed in factor 2 above), overall improvements in the reliability of the performance of the digital component/system, operational flexibility and/or maintenance-related activities may also be achieved. The design documentation contains the information that will be used to identify the intended benefits of the digital component/system and possible impacts on the likelihood of a malfunction.

5. Design Attributes/Features Design attributes of the proposed digital modification are features that serve to prevent or limit failures from occurring, or that mitigate the results/outcomes of such possible failures. Factors to be considered include the following items:
  • Design Criteria (as applicable) (e.g., diversity, independence and redundancy)
  • Inherent Design Features for Software, Hardware or the Architectural/Network (e.g., external watchdog timers, isolation devices, segmentation, self-testing and self-diagnostic features)
  • Non-concurrent Triggers
  • Sufficiently Simple (i.e., enabling comprehensive testing)
  • Unlikely Series of Events (e.g., the evaluation of a given digital modification would need to postulate multiple independent random failures in order to arrive at a state in which a SCCF is possible)
  • Failure State (e.g., always known to be acceptable)

Determination of Attributable If a CCF is determined to be not credible, then there is NO attributable impact on the likelihood of occurrence of a malfunction. Namely, if a CCF does not is sufficiently unlikely to occur, then no mechanism for an attributable impact has been created.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-36 If a CCF is determined to be credible, but the component/system is not a malfunction initiator, then there is NO attributable impact on the likelihood of occurrence of a malfunction. Namely, even if a CCF does occur, there is no relationship between the CCF and the malfunction initiator(s). Example 4-16 illustrates a case of NO attributable impact on the likelihood of occurrence of a malfunction for a SSC not being a malfunction initiator. Example 4-16. NO ATTRIBUTABLE Impact on the Likelihood of Occurrence of a Malfunction Due to a SSC Not Being a Malfunction Initiator Proposed Activity Two safety-related containment chillers exist. There are two analog control systems (one per chiller) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Affected Malfunctions and Malfunction Initiators The affected malfunction is the failure of one safety-related containment chiller. The UFSAR identifies two equipment-related initiators: (a) failure of the Emergency Diesel Generator (EDG) to start (preventing the EDG from supplying electrical power to the containment chiller it powers), (b) an electrical failure associated with the chiller system (e.g., feeder breaker failure) or a mechanical failure within the chiller itself (e.g., flow blockage). Impact on Malfunction Likelihood In this case, the safety-related chiller control system is not related to the malfunction initiators (i.e., EDG failure, breaker failure or chiller failure). Therefore, there is NO impact on the likelihood of occurrence of the malfunction that can be attributed to the digital modification. If a CCF is determined to be credible and the component/system is a malfunction initiator, then there is an attributable potential impact on the likelihood of occurrence of the malfunction. Example 4-17 illustrates the case of an attributable potential impact on the likelihood of occurrence of a malfunction for the SSC being a malfunction initiator.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-37 Example 4-17. ATTRIBUTABLE Potential Impact on the Likelihood of Occurrence of a Malfunction Due to a SSC Being a Malfunction Initiator Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Affected Malfunction and Malfunction Initiator The affected malfunction is the loss of a MFWP or the closure of a MFWP flow control valve. The UFSAR identifies an equipment-related initiator as involving the failure of a feedwater control system. Impact on Malfunction Initiator Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF causing the loss of both feedwater control systems (resulting in the loss of both MWFPs and/or the closure of both MFWP flow control valves) has been determined to be credible. Since the failure of the feedwater control systems can cause the loss of MFWPs or the closure of MFWP flow control valves, a potential impact on malfunction likelihood due to the CCF can be attributed to the digital modification. Determination of Magnitude (using Negligible/Discernable) For the case in which a CCF is credible and there is an attributable potential impact on the likelihood of occurrence of a malfunction, the magnitude portion of the criteria (i.e., negligible/discernable) also needs to be assessed. To determine the overall effect of the digital modification on the likelihood of a malfunction, examination of all the factors associated with the digital modification and their interdependent relationship need to be considered.

Formatted: Keep with next NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-38 To achieve a negligible conclusion, the examination of all the factors would conclude that the net change in the malfunction likelihood "...is so small or the uncertainties in determining whether a change in likelihood has occurred are such that it cannot be reasonably concluded that the likelihood has actually changed (i.e., there is no clear trend toward increasing the likelihood)

"[emphasis added] due to the net effect s of the factors considered (i.e., use of software ("positive"), improved hardware reliability ("positive")use of digital components, creation of a software CCF ("negative") and the, intended benefits ("positive")and design attributes/features). Alternately, if the net effects are such that a clear trend towards increasing the likelihood would result, a discernable increase in the malfunction likelihood would exist. However, to remain consistent with the guidance provided in NEI 96-07, Section 4.3.2, a discernable increase in the malfunction likelihood would NOT be more than minimal if applicable NRC requirements, as well as design, material, and construction standards, continue to be met. Examples 4-18 and 4-19 will examine the magnitude portion (i.e., negligible/discernable) of the criteria and assume the attributable portion of the criteria has been satisfied. Example 4-18 illustrates the NEGLIGIBLE impact case.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-39 Example 4-18. NEGLIGIBLE Impact in the Likelihood of Occurrence of a Malfunction Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Attributable Conclusion See Example 4-17. Magnitude Conclusion Factors Considered: 1. Software - Developed in accordance with a defined life cycle process, and complies with applicable industry standards and regulatory guidance 2. Digital Components - More reliable, comply with all applicable standards, and meet all applicable technical requirements 3. CCF - Not Credible, but the CCF likelihood is much lower than the single random hardware failure likelihood

4. Benefits - Reliability and performance increased
5. Design Attributes/Features - [LATER] Based on the factors considered, tThe net change in the likelihood of occurrence of the loss of a MFWP or the closure of a MFWP flow control valve initiated by the failure of a feedwater control system is negligible due to the interdependent effects of CCF ("negative") and use of software, use of digital devices and improved SSC performance ("positive") net effect of the factors considered. Overall Conclusion Formatted: Keep with next Formatted: Keep with next NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-40 Although an attributable potential impact on the likelihood of occurrence of the loss of a MFWP or the closure of a MFWP flow control valve was determined to exist, there was no clear trend toward increasing the likelihood. With no clear trend toward increasing the likelihood, there is not more than a minimal increase in the likelihood of occurrence of the malfunctions due to the digital modification. Example 4-19 illustrates the DISCERNABLE increase case. Example 4-19. DISCERNABLE Increase in the Likelihood of Occurrence of a Malfunction Proposed Activity Two safety-related main control room chillers exist. There are two analog control systems (one per chiller) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. The logic components/system and controls for the starting and operation of the safety injection pumps are located within the main control room boundary. The environmental requirements associated with the logic components/system and controls are maintained within their allowable limits by the main control room cooling system, which includes the chillers involved with this digital modification. Affected Malfunction and Malfunction Initiator The review of the UFSAR accident analyses identified several events for which the safety injection pumps are assumed to start and operate (as reflected in the inputs and assumptions to the accident analyses). In each of these events, the UFSAR states the following: "To satisfy single failure requirements, the loss of only one control system and its worst-case effect on the event due to the loss of one chiller has been considered in the accident analyses." Attributable Conclusion In this case, the safety-related main control room chiller control system is related to a malfunction initiator (i.e., loss of logic and/or operation function)

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-41 of the safety injection pumps. Therefore, there is a potential impact on the likelihood of occurrence of the malfunction that can be attributed to the digital modification. Magnitude Conclusion Factors Considered: 1. Software - Developed in accordance with a defined life cycle process, and complies with applicable industry standards and regulatory guidance 2. Digital Components - More reliable, comply with all applicable standards, and meet all applicable technical requirements 3. CCF - Credible, with the CCF likelihood NOT much lower than the single random hardware failure likelihood

4. Benefits - Reliability and performance increased
5. Design Attributes/Features - [LATER]. Based on the factors considered, tThe net change in the likelihood of occurrence of the malfunction of both safety injection pumps is discernable due to the net effect of the CCF ("negative") and the use of software, use of digital devices and improved SSC performance ("positives")factors considered

. Requirements/Standards Consideration Single failure criteria are no longer met. Overall Conclusion An attributable potential impact on the likelihood of occurrence of the malfunction of both safety injection pumps was determined to exist and there is a clear trend toward increasing the likelihood. The clear trend toward increasing the likelihood (i.e., the discernable increase) is due to the CCF likelihood NOT being much lower than the single random hardware failure likelihood being credible, which does not satisfy the NRC requirements associated with systems/components that must satisfy single failure requirements. With a clear trend toward increasing the likelihood and the failure to satisfy an NRC requirement, there is more than a minimal increase in the likelihood of occurrence of the malfunction of both safety injection pumps due to the digital modification.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-42 HUMAN-SYSTEM INTERFACE ASSESSMENT If no personnel-based initiators (e.g., operator error) are identified among the accident initiators, then an increase in the likelihood of the malfunction cannot occur due to the Human-System Interface portion of the digital modification. If personnel-based initiators (e.g., operator error) are identified among the malfunction initiators, then the application of the attributable criterion and the magnitude criterion (i.e., negligible/discernable) are assessed utilizing the guidance described in NEI 96-07, Section 4.3.2.

4.3.3 Does the Activity Result in More Than a Minimal Increase in the Consequences of an Accident? There is no unique guidance applicable to digital modifications for responding to this Evaluation criterion because th e identification of affected accidents and dose analysis inputs and/or assumptions are not unique for a digital modification. The guidance in NE I 96-07, Section 4.3.3 applies.

4.3.4 Does the Activity Result in More Than a Minimal Increase in the Consequences of a Malfunction? There is no unique guidance applicable to digital modifications for responding to this Evaluation criterion because the identification of the affected malfunctions and dose analysis inputs and/or assumptions are not unique for a digital modification. The guidance in NEI 96-07, Section 4.3.4 applies.

4.3.5 Does the Activity Create a Possibility for an Accident of a Different Type? INTRODUCTION From NEI 96-07, Section 3.2:

"The term 'accidents' refers to the anticipated (or abnormal) operational transients and postulated design basis accidents..." Therefore, for purposes of 10 CFR 50.59, both Anticipated Operational Occurrences (AOOs) and Postulated Accidents (PAs) fall within the definition of "accident."

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-43 From NEI 96-07, Section 4.3.5, the two considerations that need to be assessed when answering this Evaluation question are credible and bounded/related. GUIDANCE Determination of Credible If a CCF is determined to be not credible, then the creation of a possibility for an accident of a different type is NOT credible because there is no mechanism for the possibility of an accident of a different type to be created.If a CCF is determined to be credible, but the CCF likelihood is much lower than the single random hardware failure likelihood, then the creation of a possibility for an accident of a different type is NOT credible because and possible accidents of a different type are limited to those that are as likely to happen as those previously evaluated in the UFSAR.

2 If a CCF is determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood, then the creation of a possibility for an accident of a different type is credible. Determination of Bounded/Related For the case in which a CCF is credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood, causing a credible possibility for an accident of a different type to be created, the bounded/related portion of the criteria also needs to be assessed. Events/sequences currently considered in the UFSAR form the basis for comparison of events, which makes it possible to identify and evaluate the limiting case. The UFSAR evaluates a broad spectrum of accidents (i.e., initiating events and the sequences that result from various combinations of plant and safety systems response). Accidents are categorized according to expected frequency of occurrence and by type. The accident type is defined by its effect on the plant (e.g., decrease in heat removal by the secondary system, increase in heat removal by the secondary system, etc.). Characterization of accidents by type provides a basis for comparison based on events/sequences, which makes it possible to identify and evaluate the limiting cases (i.e., the cases that can challenge the analysis acceptance criteria) and eliminate non-limiting cases from further consideration.

2 Refer to NEI 96-07, Section 4.3.5, 3 rd paragraph.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-44 Therefore, a new accident that is of the same type (i.e., its effect on the plant is the same) and is within the same expected frequency of occurrence meets the bounded criterion. Alternately, a new accident that is NOT of the same type (i.e., its effect on the plant is different) and/or is NOT within the same expected frequency of occurrence does NOT meet the bounded criterion. Accidents of a different type are credible accidents that the proposed activity could create that have an impact on the type of events/sequences previously evaluated in the UFSAR. Namely, a different/new accident analysis would be needed for this different type of accident, not just a revision of a current accident analysis. Therefore, a different/new accident analysis would NOT be related to an event already been analyzed. Alternately, the revision of a current accident analysis would be related to an event already analyzed. Example 4-20 illustrates the NO CREATION of the possibility of an accident of a different type case. Example 4-20. NO CREATION of the Possibility of an Accident of a Different Type Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Malfunction / Accident Initiator The malfunction/accident initiator identified in the UFSAR for the analog main feedwater control system is the loss of one main feedwater pump (out of two pumps) due to the loss of one feedwater control system. Accident Frequency and Type The pertinent accident is the Loss of Feedwater event. The NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-45 characteristics of the Loss of Feedwater event are as follows:Type of Accident - Decrease in Heat Removal by the Secondary System Accident Category - Infrequent Incident Credible Conclusion Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF causing the loss of both feedwater control systems (resulting in the loss of both MWFPs) has been determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood. Therefore, in this case, a new accident has been created. Bounded/Related Conclusion Although the CCF causes the loss of both feedwater pumps, potentially challenging the analysis acceptance criteria (which is the focus of Evaluation Question #7), the loss of both feedwater pumps still causes the same type of accident (i.e., a decrease in heat removal by the secondary system). As identified in the UFSAR, the Loss of Feedwater event considered the loss of one main feedwater pump, allowing the safety analysis to credit a certain amount of flow from the remaining operational feedwater pump. Even though the CCF could disable both feed water pumps, the accident type and category remain bounded by a related accident because the new event would not require a "new" accident analysis, only a revision to the input parameter(s) and/or assumption(s) used in the current Loss of Feedwater accident analysis related to the operational status of the feedwater pumps. Therefore, the proposed activity does not create the possibility of an accident of a different type. Example 4-21 illustrates the CREATION of the possibility of an accident of a different type case. Example 4-21. CREATION of the Possibility of an Accident of a Different Type Proposed Activity Two non-safety-related analog feedwater control systems and one non-safety-NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-46 related main turbine steam-inlet valves analog cont rol system exist.The two feedwater control systems and the one main turbine steam-inlet valves control system will be combined into a single digital control system. Malfunction / Accident Initiator The identified feedwater control system malfunctions include (a) failures causing the loss of all feedwater to the steam generators [evaluated in the Loss of Feedwater event] and (b) failures causing an increase in main feedwater flow to the maximum output from both MFWPs [evaluated in the Excess Feedwater event]. The identified main turbine steam-inlet valve control system malfunctions include (a) all valves going fully closed causing no steam to be admitted into the turbine [evaluated in the Loss of Load event] and (b) all valves going fully open causing excess steam to be admitted into the turbine [evaluated in the Excess Steam Demand event]. Accident Frequency and Type The characteristics of the pertinent accidents are as follows: Loss of Feedwater: Type of Accident - Decrease in Heat Removal by the Secondary System Accident Category - Infrequent Incident Excess Feedwater: Type of Accident - Increase in Heat Removal by the Secondary System Accident Category - Moderate Frequency Incident Loss of Load: Type of Accident - Decrease in Heat Removal by the Secondary System Accident Category - Moderate Frequency Incident NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-47 Excess Steam Demand: Type of Accident - Increase in Heat Removal by the Secondary System Accident Category - Moderate Frequency Incident Credible Conclusion Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF impacting both the feedwater control systems and the main turbine steam-inlet valves control system has been determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood. Therefore, in this case, the following conditions are credible: (1) Loss of both feedwater pumps (2) Increase in main feedwater flow to the maximum output from both MFWPs. (3) All main turbine steam-inlet valves going fully closed (4) All main turbine steam-inlet valves going fully open (5) Combination of (1) and (3) (6) Combination of (1) and (4) (7) Combination of (2) and (3) (8) Combination of (2) and (4) Conditions (1) though (4) are already considered in the UFSAR, so these do not create a new accident. Since conditions (1) through (4) do not create a new accident, they do not create the possibility for an accident of a different type. Conditions (5) through (8) are not considered in the UFSAR, so four new accidents have been created.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-48 Bounded/Related Conclusion Based on the current set of accidents identified in the UFSAR, the UFSAR accident analyses do not consider a simultaneous Feedwater event (i.e., Loss of Feedwater or Excess Feedwater) with a Main Steam event (i.e., Excess Steam Demand or Loss of Load). Condition (5) still causes a decrease in heat removal by the secondary system.Condition (6) involves both a decrease and an increase in heat removal by the secondary system. Condition (7) involves both a decrease and an increase in heat removal by the secondary system. Condition (8) still causes an increase in heat removal by the secondary system. The new accidents created in Conditions (5) though (8) are NOT bounded by a related accident because new accident analyses will be needed. Therefore, the proposed activity does create the possibility of an accident of a different type.

4.3.6 Does the Activity Create a Possibility for a Malfunction of an SSC Important to Safety with a Different Result? INTRODUCTION From NEI 96-07, Section 4.3.6, the two considerations that need to be assessed when answerin g this question are credible and bounded. GUIDANCE Determination of Credible If a CCF is determined to be not credible, then the creation of a possibility for a malfunction with a different result is NOT credible because there is no mechanism for the possibility of a malfunction with a different result to be created.If a CCF is determined to be credible, but the CCF likelihood is much lower than the single random hardware failure likelihood, then the creation of a possibility for a malfunction with a different result is NOT credible NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-49 because and possible malfunctions with a different result are limited to those that are as likely to happen as those previously evaluated in the UFSAR.

3 If a CCF is determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood, then the creation of a possibility for a malfunction with a different result is credible. Determination of Bounded For the case in which a CCF is credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood, causing a credible possibility for a malfunction with a different result to be created, the bounded portion of the criteria also needs to be assessed. Types of Malfunctions to be Considered:

NEI 96-07, Section 4.3.6 states:

"In evaluating a proposed activity against this criterion, the types and results of failure modes of SSCs that have previously been evaluated in the UFSAR and that are affected by the proposed activity should be identified. This evaluation should be performed consistent with any failure modes and effects analysis (FMEA) described in the UFSAR, recognizing that certain proposed activities may require a new FMEA to be performed." [emphasi s added] Based on this excerpt, both previously-evaluated malfunctions and new malfunctions need to be considered when developing the response to this Evaluation question. Typically, a new FMEA will be necessary for a digital modification since the original considerations for malfunctions did not take into account the unique aspects of a digital modification (e.g., the possibility of a software CCF). Sources of Results:

NEI 96-07, Section 4.3.6 states:

"Attention must be given to whether the malfunction was evaluated in the accident analyses at the component level or the overall system level

." [emphasis added]

3 Refer to NEI 96-07, Section 4.3.6, 4 th paragraph.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-50 Accident analyses are typically included and described in UFSAR Chapters 6 and 15 (or equivalent). The phrase "was evaluated in the accident analyses" refers to how the malfunction was addressed in the accident analysis (e.g., failure to perform a design function, failure to cease performing a design function, etc.) and the level at which the malfunction was addressed in the accident analysis (e.g., component, train, system, etc.). Types of Results:

In NEI 96-07, Section 4.3.6, the second bullet/example after the first paragraph states:

"Provided the end result of the component or subsystem failure is the same as, or is bounded by, the results...described in the UFSAR..., then...[the activity]...would not create a 'malfunction with a different result'." [emphasis added] Many types of results can be described in a UFSAR. The focus on the end result implies the possible existence of other non-end results. For clarity, all results other than the end result will be identified as intermediate results. No intermediate results need to be considered. As a general example, consider the following possible levels of malfunction results that could be described in a UFSAR:

  • Component Level Result
  • System Level Result (from the component level malfunction)
  • Plant Level Result (from the system level malfunction) In this generalized example, the Component Level and System Level results would be considered intermediate results and the Plant Level result would be considered the end result. Only the Plant Level result is pertinent and needs to be considered when determining if the possibility of a malfunction with a different result has been created. Example 4-22 illustrates the NO CREATION of the possibility of a malfunction with a different result case. Example 4-22. NO CREATION of the Possibility of a Malfunction with a Different Result NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-51 Proposed Activity Two non-safety-related main feedwater pumps (MFWPs) exist, each with its own flow control valve. There are two analog control systems (one per MFWP and flow control valve combination) that are physically and functionally the same. Each analog control system will be replaced with a separate digital control system. The hardware platform for each digital control system is from the same supplier and the software in each digital control system is exactly the same. Malfunction / Accident A malfunction identified in the UFSAR for the analog main feedwater control systems involves the loss of one main feedwater pump (out of two pumps), which is evaluated in the Loss of Feedwater accident analysis. Credible Conclusion Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF impacting both feedwater control systems has been determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood. Bounded Conclusion Types of Malfunctions: A CCF can cause the loss of both main feedwater pumps. Source of Result: Currently, the malfunction of the MFWP is evaluated to "stop" and the malfunction is evaluated at the component level (i.e., the "pump" is assumed to stop). Assuming the CCF occurs, the malfunction will continue to be evaluated as the "stopping" of MFWPs and the level of the malfunction remains at the component level (i.e., the "pump").

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-52 Type of Result: The UFSAR identifies the malfunction of one main feedwater pump as causing a reduction in flow (intermediate result) to the steam generators, which initiates a Loss of Feedwater event (end result). The loss of both main feedwater pumps causes no flow to the steam generators ("new" intermediate result), which still initiates the Loss of Feedwater event ("new" end result). In both instances, the end result is the Loss of Feedwater event. Overall Conclusion Although the impact of the intermediate result on the accident analysis acceptance criteria is most likely more severe (by going from the loss of one pump to the loss of both pumps), the result of the CCF is bounded. Therefore, the proposed activity does NOT create the possibility of a malfunction with a result. Example 4-23 illustrates the CREATION of the possibility of a malfunction with a different result case. Example 4-23. CREATION of the Possibility of a Malfunction with a Different Result Proposed Activity Two non-safety-related analog feedwater control systems and a separate analog control system that controls the main turbine steam-inlet valves exist.All three analog control systems will be replaced with one digital control that will combine the two feedwater control systems and the ma in turbine steam-inlet valves control system into a single digital device. Malfunction / Accident From the UFSAR, the identified feedwater control system malfunctions include (a) failures causing the loss of all feedwater to the steam generators [evaluated in the Loss of Feedwater accident analysis] and (b) failures causing an increase in main feedwater flow to the maximum output from both MFWPs [evaluated in the Excess Feedwater accident analysis]. From the UFSAR, the identified main turbine steam-inlet valve control NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-53 system malfunctions include (a) all valves going fully closedcausing no steam to be admitted into the turbine [evaluated in the Loss of Load accident analysis] and (b) all valves going fully open causing excess steam to be admitted into the turbine [evaluated in the Excess Steam Demand accident analysis]. Credible Conclusion Based on the technical outcome from the CCF Susceptibility Analysis and the Failure Modes and Effects Analysis (FMEA) performed as part of the technical assessment supporting this digital modification, a software CCF impacting the feedwater control systems and the main turbine steam-inlet valve control system has been determined to be credible and the CCF likelihood is NOT much lower than the single random hardware failure likelihood. Bounded Conclusion Types of Malfunctions: A CCF can cause any of following conditions: (1) Loss of both feedwater pumps (2) Increase in main feedwater flow to the maximum output from both MFWPs. (3) All main turbine steam-inlet valves going fully closed (4) All main turbine steam-inlet valves going fully open (5) Combination of (1) and (3) (6) Combination of (1) and (4) (7) Combination of (2) and (3) (8) Combination of (2) and (4) Source of Result: Currently, the malfunctions are evaluated as affecting only one system (i.e., feedwater control or main turbine control, NOT both) and the malfunctions are evaluated at the component level (i.e., "pump" or "valve").

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-54 Assuming the CCF occurs, the malfunction will no longer affect only one system, but will continue to be evaluated at the component level (i.e., "pump" or "valve"). Type of Result: The UFSAR identifies the end result of a malfunction as causing a Feedwater event or a Main Steam event, NOT both. In Conditions (5) through (8), the end result is no longer a Feedwater event or a Main Steam event. Overall Conclusion Based on the current set of accidents identified in the UFSAR, the accident analyses do not consider a simultaneous Feedwater/Main Steam event. The different results [simultaneous accidents in Conditions (5) though (8)] are NOT bounded by the previously-evaluated results of only one accident. Therefore, the proposed activity does create the possibility of a malfunction with a different result.

4.3.7 Does the Activity Result in a Design Basis Limit for a Fission Product Barrier Being Exceeded or Altered? There is no unique guidance applicable to digital modifications for responding to this Evaluation question because the identification of possible design basis limits for fission product barriers and the process for determination of "exceeded" or "altered" are not unique for a digital modification. The guidance in NEI 96-07, Section 4.3.7 applies.

4.3.8 Does the Activity Result in a Departure from a Method of Evaluation Described in the UFSAR Used in Establishing the Design Bases or in the Safety Analyses? There is no unique guidance applicable to digital modifications for responding to this Evaluation criterion because activities involving methods of evaluation do not involve SSCs. The guidance in NEI 96-07, Section 4.3.8 applies.

NEI 96-07, Appendix D NEI Proposed Modifications: May 16, 2017 D-55 5.0 EXAMPLES [LATER]

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