- •Iaea safety standards
- •Objective
- •Structure
- •Relationship to other standards
- •2. Management systems for I&c design
- •2.8. The management systems for development of I&c systems should comply with the recommendations of Safety Guides gs-g-3.1, Ref. [5] and gs-g-3.5, Ref. [6].
- •Generic management system processes
- •Configuration management
- •2.15. All I&c configuration items and their associated configuration documents should be designated, given a unique identification, and placed under configuration control.
- •2.31. Insights gained from probabilistic safety assessments (psAs) should be considered in the design of I&c systems.
- •Documentation
- •2.33. Before I&c systems are declared operable their documentation should be complete and should reflect the as-built configuration.
- •2.34. I&c documentation should:
- •2.36. I&c documents should be grouped according to their primary or secondary role in the design process.
- •2.38. Documentation for I&c systems and components should, as a minimum, cover the following topics:
- •3. Design bases
- •Inputs to I&c design bases
- •Identification of I&c functions
- •3.4. The required functions of the I&c systems should be determined as part of the nuclear power plant design process.
- •Content of I&c design bases
- •3.7. The overall I&c system architecture and each I&c system should have a design basis.
- •3.9. The I&c systems required for the safety of the plant should be identified systematically.
- •3.10. I&c system design bases should specify the following:
- •3.12. In addition to the above the design basis for the reactor protection system should specify the following:
- •Variables and states that must be displayed so that the operators can confirm the operation of protective system functions;
- •4. Guidance for overall I&c system architecture architectural design
- •4.3. The overall I&c architecture should:
- •4.4. The inputs to the overall I&c architecture design process should refer to the plant safety design basis documents, which should provide the following information:
- •Defence in depth
- •4.28. When diverse I&c systems are provided to meet requirements for defence-in-depth, the diverse systems should not both be subject to the same errors in design or fabrication.
- •5. Safety classification of I&c functions, systems, and equipment
- •6. Life cycle activities
- •Process implementation
- •Verification that the effects of automatic control system failures will not exceed the acceptance criteria established for anticipated operational occurrences.
- •6.58. The I&c architecture should be designed to fully satisfy the system requirements, including system interfaces and non-functional requirements (e.G., performance and reliability).
- •6.109. The benefits of changes should be weighed against potential negative safety consequences and this assessment documented as part of the justification for the changes.
- •Design for reliability
- •Single failure criterion
- •7.10. Each safety group should perform all actions required to respond to a pie in the presence of:
- •7.15. Non-compliance with the single failure criterion should be exceptional and clearly justified in the safety analysis.
- •7.19. I&c systems should be redundant to the degree needed to meet design basis reliability requirements.
- •Independence
- •7.27. When isolation devices are used between systems of different safety importance, they should be a part of the system of higher importance.
- •7.29. The adequacy of design features provided to meet the independence recommendations should be justified. Physical separation
- •7.31. Items that are part of safety systems should be physically separated from items of lower safety classification.
- •7.32. Redundant items of safety systems should be physically separated from each other.
- •Electrical isolation
- •Diversity
- •7.49. The decision to use diversity or not use diversity should be justified.
- •7.50. Where diversity is provided to cope with ccf several types of diversity should be used.
- •7.51. Where diversity is provided the choice of the types of diversity used should be justified.
- •Failure modes
- •7.57. The failure modes of I&c components should be known and documented.
- •7.60. Failures of I&c components should be detectable by periodic testing or self-revealed by alarm or anomalous indication.
- •7.73. Analysis that is part of the evidence of equipment qualification should include a justification of the methods, theories and assumptions used.
- •7.75. Traceability should be established between each installed system and component important to safety and the applicable evidence of qualification.
- •Suitability and correctness
- •7.81. The equipment qualification program should demonstrate that the as-built I&c systems and installed components correctly implement the qualified design.
- •7.90. Environmental qualification of safety components that must operate in harsh environments should include type testing.
- •7.102. Detailed emc requirements should be determined for safety systems and components and their compliance with the requirements demonstrated.
- •7.105. Equipment and systems, including associated cables, should be designed and installed to withstand the electromagnetic environment in which they are located.
- •7.109. Limits on radiated and conducted electromagnetic emissions should be established for all plant equipment.
- •7.112. The equipment qualification program should show that electromagnetic emissions of plant equipment are within the defined limits.
- •7.114. Instrumentation cables should have twisting and shielding sufficient to minimize interference from electromagnetic and electrostatic interference.
- •Design to cope with ageing
- •7.119. Ageing mechanisms that could significantly affect I&c components and means for following the effects of these mechanisms should be identified during design.
- •7.122. Maintenance programs should include activities to identify any trend towards degradation (ageing) that could result in the loss of operability of equipment.
- •Control of access to systems important to safety
- •7.130. Access to equipment in I&c systems should be limited to prevent unauthorized access and to reduce the possibility of error.
- •Testing and testability during operation
- •Test provisions
- •7.150. Arrangements for testing should neither compromise the independence of safety systems nor introduce the potential for common cause failures.
- •Test interfaces
- •7.153. Provisions for testing I&c systems and components should:
- •7.154. Where equipment to be tested is located in hazardous areas, facilities should be provided to allow testing from outside the hazardous area.
- •7.164. The test program should define processes for periodic tests and calibration of systems that:
- •Individually test each sensor, to the extent practicable.
- •7.165. In addition to the recommendations of paragraph 7.164, the processes defined for periodic tests and calibration of safety systems should:
- •Independently confirm the functional and performance requirements of each channel of sense, command, execute, and support functions;
- •Include as much of the function under test as practical (including sensors and actuators) without jeopardizing continued normal plant operation;
- •Maintainability
- •7.169. The design of I&c systems should include maintenance plans for all systems and components.
- •Setpoints
- •7.185. Trip setpoints used to initiate safety actions should be selected to ensure that required mitigating actions occur before the monitored variable reaches the analytical limit.
- •Operational identification of items important to safety
- •7.186. A consistent and coherent method of naming and identifying all I&c components should be determined and followed throughout the design, installation and, operation phases of the plant.
- •7.190. I&c components in the plant should be marked with their identifying information.
- •8.4. To the extent practicable, the plant conditions of concern should be monitored by direct measurement rather than being inferred from indirect measurements.
- •8.17. Means should also be provided to manually initiate the mechanical safety systems and the individual components necessary to initiate and control performance of their safety functions.
- •Digital computer systems and digital equipment
- •8.68. Specific skilled staff should be available during operation to allow controlled software and configuration data changes to be made when necessary to computer based systems.
- •8.91. Data received and data transmitted should be stored in separate, pre-determined memory locations.
- •8.154. Tools should be used to support all aspects of the I&c life cycle where benefits result through their use and where tools are available.
- •8.173. Confirmation of the suitability and correctness of industrial digital devices for their intended functions should produce evidence:
- •V&V at each stage of development for the final product;
- •9.4. The I&c system should allow the operator in the control room to initiate or take manual control of each function necessary to control the plant and maintain safety.
- •9.21. Instrumentation performing the functions given in 9.20 items a, b, and c should be classified as safety systems.
- •9.32. The main control room, the supplementary control room, and the Emergency Control Centre should have at least two diverse communications links with:
- •9.42. The Human System Interface (hmi) design should retain positive features and avoid hfe issues and problems of previous designs.
- •9.57. Where hmi stations are distributed, plant staff should have means to access these different locations in a safe and timely manner.
- •10.4. Development of software for systems should follow a previously defined life cycle, be duly documented and include thorough verification and validation. (See Chapter 6.)
- •10.49. Coding rules should be prescribed and adherence verified.
- •10.72. Verification should include the following techniques:
- •Software tools
- •Glossary
- •Annex I defense in depth in I&c systems
- •Annex II traceability to previouse I&c safety guides
- •Annex III bibliography of supporting international standards
Confirmation of correct system behaviour following power interruptions and restart or reboot.
Verification that the effects of automatic control system failures will not exceed the acceptance criteria established for anticipated operational occurrences.
6.32. Each assumption of an analysis should be stated, and justified in that analysis.
6.33. The methodology for any analysis conducted should be thoroughly defined and documented together with analysis inputs, results, and the analysis itself.
6.34. The analyses recommend by paragraph 6.31 are part of the plant safety assessment as described by NS-G-1.2, Ref. [10]. NS-G-1.2, Ref. [10] provides additional guidance on safety assessment.
6.35. Reliability claims for any I&C system that is based upon a common platform, regardless of technology, should be limited to 10-5/demand, regardless of the extent of to which the strategies described in Chapter 6 (e.g., redundancy) are employed.
6.36. Reliability claims for any individual I&C system that is based upon a common computer based platform, should be limited to 10-4/demand, regardless of the extent of to which the strategies described in Chapter 7 (e.g., redundancy) are employed.
System requirements
6.37. Requirement Engineering is an important factor for safety properties of digital I&C systems that are important to safety.
6.38. Requirement Engineering should allow developers to manage system requirements throughout the product life cycle to ensure that all requirements are implemented, checked and tested.
6.39. A System Requirements Specification should define what the I&C system must do, and must not do, within the context of the entire application.
6.40. The origin of and rationale for every requirement should be defined, to facilitate verification, traceability to higher level documents and a demonstration that all relevant design basis requirements have been accounted for.
6.41. Requirements essential to the functions important to safety should be distinct from all other requirements. Requirements that are not important to safety should be shown not to affect the functions important to safety (see paragraph 6.59).
6.42. The System Requirements Specification should explicitly define all relations between inputs and outputs for each of the operating modes.
6.43. Requirements should be described in terms understandable to all parties concerned (e.g.; the licensee, suppliers, and designers).
Hazards analysis
6.44. Hazards analyses should be performed for the I&C systems and the overall I&C architecture and the functionality within them to identify all potential system hazards that might compromise the I&C systems' safety functions.
6.45. These system hazards should be translated into system requirements that will serve to minimize, eliminate, or mitigate the effects of such hazards.
6.46. As the I&C progresses system’s interaction with the plant should be re-evaluated as part of the plant safety assessment detect and correct features of the detailed implementation that conflict with the goal of meeting the requirements for management of safety, the principal technical requirements, and the requirements of SSR 2/1. Ref. [1]. See NS-G-1.2, Ref. [10].
6.47. New or modified requirements or design features should be developed to deal with new contributions to hazards that are identified by the on-going hazard analysis.
I&C system validation planning
6.48. Validation should cover all requirements and specify the expected results for each test.
6.49. Items to be demonstrated by validation include, for example, the of full ranges (including out-of-range values for interface signals), exceptions handling, timing related requirements, set-point accuracies and hysteresis, demonstration that the system responds safely to all possible interface and load conditions, and coverage of all modes of operation of the system, including transition between modes and recovery after power failure.
6.50. The system validation plan should have provisions to test all parts of the system using realistic scenarios involving all inputs (dynamic testing).
6.51. The dynamic tests should be based on an analysis of the possible plant scenarios.
6.52. The test profiles should be representative of the expected plant parameter variations that would place demands on the I&C system.
6.53. The number of tests executed should be sufficient to provide confidence in the system’s dependability.
I&C system design
6.54. The system requirements that are to be satisfied by the I&C system should be mapped to an appropriate combination of hardware, devices configured with HDL, and software (if present).
6.55. Hardware might include application specific integrated circuits. Software might include pre-existing software and firmware, such as the operating system, software to be developed and/or software to be produced by configuring pre-developed software.
6.56. Chapter 10 gives recommendations for refining the system requirements for software into software requirements.
6.57. The refined requirements might also have to account for lower level design decisions made for parts of the system outside the I&C system, e.g. the type and performance of actuated devices.