BS EN 60987-2009 pdf download.Nuclear power plants — Instrumentation and control important to safety — Hardware design requirements for computer-based systems.
5.1.3 Hardware requirements shall be presented according to a technique or method whose format shall not preclude readability, i.e. the hardware requirements should not be difficult to understand.
5.1.4 Functional hardware requirements shall be unambiguous. testable and/or verifiable and achievable.
5.1.5 The hardware requirements specification should give an overview of hardware requirements, identify the hardware functions important to nuclear safety (however, if these are provided in combination with the system software they should be defined in the system requirements specification), identify the hardware design requirements, state hardware reliability requirements, and state the hardware environmental withstand requirements.
5.1.6 The hardware requirements for computer systems may include requirements which are applicable to hardware in general as well as requirements which are particular to computer system hardware (for example; cabling, surface preparation of enclosures).
5.1.7 The hardware functional requirements should generally describe what has to be done and not how it has to be done. However, the use of pre-existing components/platforms may result In a degree of bottom-up hardware design. Before such pre-existing components are selected for use, an assessment shall be performed to confirm that the hardware performance characteristics (for example: failure modes) are consistent with system requirements. If any anomalies are found then these shall be reconciled, either by modifying the hardware design or the system design (while ensuring that system nuclear safety requirements are not compromised).
5.2 Functional and performance requirements
5.2.1 The hardware functional and performance requirements shall be consistent with the functional and performance requirements of the system important to safety.
5.2.2 The hardware functional and performance requirements, combined with the software requirements (to the extent necessary to address all hardware requirements), shall be verified for compliance with the system requirements.
5.2.3 All parts of the system, down to the component level, which contain software shall be assessed as described in 1.2 of this standard.
a) The hardware functional requirements shall include, but are not restricted to, the definition of
1) the purpose of the overall computer system hardware and of each hardware subsystem:
5.3 Reliability/Availability requirements
5.3.1 The hardware reliability/availability requirements shall be consistent with the overall reliability requirements of the system. They shall include a description of any types of failure which have to be tolerated without loss, or with a defined limited loss, of function. Hardware reliability targets should be provided.
NOTE Hardware reliability in this context is concerned with random hardware failures and excludes any consideration of failures due to logical design errors.
5.32 Irrespective of the hardware reliability/availability requirements, the overall I&C architecture for a NPP shall meet the IAEA NS-G-1 .3 single failure criteria (see 3.6).
5.3.3 The hardware requirements should give target figures for the hardware reliability parameters (such as mean time between failure (revealed), mean time between failure(unrevealed), mean time to repair (for revealed failures)). Any requirement for reliability claims to be supported with detailed analysis of the hardware design should be stated, for example, subunit, card-level or component-level analysis.
5.3.4 The methods which may be used to analyse the reliability and the effects of system hardware failures include
— FTA. which is concerned with the identification and analysis of conditions and factors which cause or contribute to the occurrence of a defined undesirable event (see IEC 61025 for advice concerning this technique);
— FMEA. which identifies failures which have significant consequences affecting the system performance, for example, reliability, safety, availability (see IEC 60812 for advice concerning this technique).
Where relevant, a suitable analysis technique shall be applied to Class 1 and Class 2 hardware systems to ensure that any potential hardware failures do not have unacceptable nuclear safety effects.
5.3.5 A technique such as FTA when combined with known component failure data may be used to provide calculated values for system hardware reliability characteristics. Such an approach shall be used to analyse the hardware of Class 1 systems (see IEC 61513), unless sufficient operating experience is available to give high confidence that the target hardware reliability targets will be achieved. Such a technique should also be applied for Class 2 systems, or, alternatively, a justification of adequate reliability provided on the basis of qualitative reasoning (for example, quality of components, hardware redundancy, operating experience, proportion of revealed hardware failures versus unrevealed hardware failures. etc.), particularly if hardware reliability requirements are not overly demanding.BS EN 60987-2009 pdf download.