Glossary


Analog technology

A device in which data are represented by a continuously variable quantity.


Code of Federal Regulations (10 CFR 50, 10 CFR 50.59, 10 CFR 50.90)

The Code of Federal Regulations, Title 10, Part 50, governs the licensing of domestic nuclear power plants. Section 50.59 sets forth criteria for determining whether changes to a licensed nuclear power plant require prior USNRC approval. Appendix A of 10 CFR 50 lists ''general design criteria" to be followed in the design, construction, and operations of nuclear power plants.

Combinational logic

A Boolean algebraic function whose output value is determined by the present conditions (or current inputs), i.e., there is no "state" or memory.

Common-cause failure

Multiple component failures having the same cause.

Common-mode failure

The failure of multiple components in the same way. Both common-cause and common-mode failures arise when the assumption of independence of the failures of the components is violated. Common-mode failures are a concern when the failures occur concurrently or at least sequentially in a time frame before the minimum number of component is recovered.

Common-mode software failure

Failure of redundant sets of software in the same way.

Configuration control/management

A discipline applying technical and administrative direction and surveillance to identify and document the functional and physical characteristics of a configuration item, control changes to those characteristics, record and report change processing and implementation status, and verify compliance with specified requirements (ANSI/IEEE 610.12-1990).


Dedication

The qualification process performed on commercial-grade items proposed for use in safety systems to assure an equivalent level of quality as obtained for components developed and produced under the formal quality programs of Title 10 CFR Part 50, Appendix B.

Defense-in-depth

The conservative design approach that uses multiple, layered systems to provide alternate means of accomplishing different functions related to common goals. This approach provides added protection against natural phenomena and plant operational transients and accidents.

Design basis

Information on plant functional components and their response to a set of postulated failure scenarios.

Design faults (vs. random faults)

Design faults are those committed during the original design or during subsequent modifications and cause the system that is actually implemented to be different from that which was intended. Design faults can be contrasted with physical faults (sometimes called random faults) which occur during operation, caused by internal or external physical phenomena (wear-out, electromagnetic perturbations, temperature, vibration, etc.).

Digital (technology)

A device in which data are represented by a combination of discrete digits, such as 0's and 1's.

Diversity

The use of two or more mutually exclusive means of performing the same function. This includes design, functional, and "nameplate" diversity. Design diversity is the use of two or more components with a different internal design to accomplish the same function. Functional diversity is the use of two or more components to achieve different component functions, although the functions may be related in terms of higher-level functions and requirements. Nameplate diversity is the use of components from different manufacturers to accomplish the same function.


Engineered safety features actuation system

A set of plant components that work with the reactor protection system to initiate rapid and complete response actions in response to plant transients and accidents.

Environmental qualification

A set of testing and certification procedures to assure the operation of nuclear components in anticipated environmental conditions.


Formal methods

The use of specifications with mathematically defined semantics and mathematical analysis techniques defined for these specifications.



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OCR for page 111
Glossary Analog technology A device in which data are represented by a continuously variable quantity. Code of Federal Regulations (10 CFR 50, 10 CFR 50.59, 10 CFR 50.90) The Code of Federal Regulations, Title 10, Part 50, governs the licensing of domestic nuclear power plants. Section 50.59 sets forth criteria for determining whether changes to a licensed nuclear power plant require prior USNRC approval. Appendix A of 10 CFR 50 lists ''general design criteria" to be followed in the design, construction, and operations of nuclear power plants. Combinational logic A Boolean algebraic function whose output value is determined by the present conditions (or current inputs), i.e., there is no "state" or memory. Common-cause failure Multiple component failures having the same cause. Common-mode failure The failure of multiple components in the same way. Both common-cause and common-mode failures arise when the assumption of independence of the failures of the components is violated. Common-mode failures are a concern when the failures occur concurrently or at least sequentially in a time frame before the minimum number of component is recovered. Common-mode software failure Failure of redundant sets of software in the same way. Configuration control/management A discipline applying technical and administrative direction and surveillance to identify and document the functional and physical characteristics of a configuration item, control changes to those characteristics, record and report change processing and implementation status, and verify compliance with specified requirements (ANSI/IEEE 610.12-1990). Dedication The qualification process performed on commercial-grade items proposed for use in safety systems to assure an equivalent level of quality as obtained for components developed and produced under the formal quality programs of Title 10 CFR Part 50, Appendix B. Defense-in-depth The conservative design approach that uses multiple, layered systems to provide alternate means of accomplishing different functions related to common goals. This approach provides added protection against natural phenomena and plant operational transients and accidents. Design basis Information on plant functional components and their response to a set of postulated failure scenarios. Design faults (vs. random faults) Design faults are those committed during the original design or during subsequent modifications and cause the system that is actually implemented to be different from that which was intended. Design faults can be contrasted with physical faults (sometimes called random faults) which occur during operation, caused by internal or external physical phenomena (wear-out, electromagnetic perturbations, temperature, vibration, etc.). Digital (technology) A device in which data are represented by a combination of discrete digits, such as 0's and 1's. Diversity The use of two or more mutually exclusive means of performing the same function. This includes design, functional, and "nameplate" diversity. Design diversity is the use of two or more components with a different internal design to accomplish the same function. Functional diversity is the use of two or more components to achieve different component functions, although the functions may be related in terms of higher-level functions and requirements. Nameplate diversity is the use of components from different manufacturers to accomplish the same function. Engineered safety features actuation system A set of plant components that work with the reactor protection system to initiate rapid and complete response actions in response to plant transients and accidents. Environmental qualification A set of testing and certification procedures to assure the operation of nuclear components in anticipated environmental conditions. Formal methods The use of specifications with mathematically defined semantics and mathematical analysis techniques defined for these specifications.

OCR for page 111
Generic Letter (95-02) Guidance from the USNRC on review of digital I&C upgrades based on an endorsement of EPRI TR-102348, "Guideline on Licensing Digital Upgrades." Graded approach Tailoring of review process and resources based on the safety significance of the proposed action. Hazard analysis A structured process for analyzing a system to identify potential hazards and their root causes. Human-machine interface (also called human-system interface and human-computer interface). For the purposes of this report, the interactions of plant personnel with the digital I&C system, including the effects of computer displays, plant operations, and I&C maintenance. Independence Noninteracting or noninterfering components. A set of components has "statistical independence" when the joint probability of a compound event among the set of components equals the product of the probabilities of the individual events that make up the compound event. Instrumentation and control Systems that provide plant monitoring, control, and protection functions in nuclear power plants. Mean time between failures A statistical estimation of the average time between failures. Memory sharing The use of common memory storage for different functions that use a common historical data base. Multiplexing Transmission of data signals across shared pathways. A multiplexer is a digital switch, connecting data from one of many sources to its output. Multitasking "Simultaneous" execution of several tasks (processes) on a single computer processor. The operating system controls the switching between the different tasks. N-version programming The development of different versions of a software program to achieve the same function by different design teams in an effort to achieve fault tolerance. Probabilistic (risk) assessment method An analysis method used to (a) assess the relative frequency and consequences of postulated events, (b) search for design weaknesses, and (c) identify and assess the frequency and associated risk of improbable events which are beyond the plant design basis. Reactor protection system A set of plant components that initiate rapid and complete response actions in response to plant transients and accidents to bring the reactor to a safe condition. Redundancy The use of identical or diverse items to provide alternate means of performing a required function in the event of failure of an individual item. Redundancy is used primarily as defense against "random" or wear-out failures when no diversity is provided. Safety analysis report The formal documentation of the basis for licensing a nuclear power plant. Safety-critical application Systems whose failure or malfunction could cause or contribute to an accident. Safety margin assessment Assessment of (a set of) design criteria relative to known failure criteria. Safety (and nonsafety) systems Those systems relied upon to remain functioning during and following design basis events to ensure (a) the integrity of the reactor coolant pressure boundary, (b) the capability to shutdown the reactor and maintain it in a safe shutdown condition, or (c) the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures comparable to the 10 CFR 100 guidelines (IEEE 603-1991). Separation Physical or functional independence of systems. Sequential logic A Boolean algebraic function whose output value is determined from the current inputs as well as the current "state" which is typically stored in memory elements or delay-inducing feedback loops. Software quality assurance Development processes and standards that attempt to produce software with certain specified qualities. Software specification A description of a piece of software which is a basis for its design and implementation. Standard Review Plan (and Branch Technical Positions, Regulatory Guides) A set of guidance for USNRC reviewers as to what is needed from the licensee to assess the adequacy of a proposed design or what represents a satisfactory method of complying with the licensing requirements. Branch technical positions, regulatory guides, and industry standards provide additional, more detailed guidance. Static analysis Either manual or automated analysis of software source code to detect potential errors without executing the code. Thread auditA software code review procedure that traces a particular software program function from input to output. Unreviewed safety questionA failure mode not previously analyzed in a plant's safety analysis report. Verification and validation Verification is the process of determining whether or not the product of each stage of the system design process fulfills the requirements imposed by the previous design stage. Validation is the test and evaluation of the integrated system design to ensure compliance with the functional, performance, and interface requirements as specified in the system functional requirements (IEEE 7-4.3.2 and IEC 880).