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I&C Safety Guide DRAFT 20110803.doc
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7.114. Instrumentation cables should have twisting and shielding sufficient to minimize interference from electromagnetic and electrostatic interference.

7.115. DS-430, Ref. [14] gives recommendations for grounding, cable selection, and cable routing to reduce production and propagation of electromagnetic interference.

Design to cope with ageing

7.116. SSR 2/1 Requirement 31 states that:

The design life of items important to safety shall be evaluated and specified. Appropriate margins shall be provided in the design to take into account relevant mechanisms of ageing, neutron embrittlement and wear-out and the potential for age related degradation, to ensure the capability of the items important to safety to perform their necessary safety function throughout its design life.

The design for a nuclear power plant shall take due account of ageing and wear-out effects in all operational states for which a component is credited, including testing, maintenance, maintenance outages, plant states in a postulated initiating event and plant states following a postulated initiating event.

Provision shall be made for monitoring, testing, sampling and inspection, to assess ageing mechanisms predicted at the design stage and to help identify unanticipated behaviour or degradation that may occur in service

7.117. The qualified service life of electrical and electronics systems and components might be considerably less than plant life.

7.118. Age degradation that impairs the ability of a safety component to function under severe environmental conditions might exist well before the functional capabilities under normal conditions are noticeably affected.

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.

7.120. Identification of potential ageing impacts involves first understanding of the relevant ageing phenomena for the various I&C components.

7.121. Ageing is most commonly due to heat, and radiation exposure. Nevertheless, the possibility that other phenomena (e.g., mechanical vibration, or chemical degradation) might be relevant to a specific component must be considered.

7.122. Maintenance programs should include activities to identify any trend towards degradation (ageing) that could result in the loss of operability of equipment.

7.123. Examples of monitoring techniques include:

  • Equipment testing (of plant components or components subject to ageing representative of plant components);

  • Visual inspections; and

  • Analysis of operating experience

7.124. Examples of means to address ageing impacts include:

  • Component replacement before the end of its qualified life;

  • Adjustment of functional characteristics (e.g., recalibration) to account for ageing effects; and

  • Changes to maintenance procedures or environmental conditions that have the effect of slowing the ageing process.

7.125. The qualified life of safety components that must perform their safety function in harsh environments should be determined and these components should be replaced before the end of their qualified life.

7.126. On-going qualification might show that the qualified life of a component is validated or is indicated to be different than the expected lifetime. Information from on-going qualification may be used to increase or decrease the qualified life of a component.

7.127. NS-G-2.12, Ref. [23] gives additional guidance on ageing management including the interface between equipment qualification and the ageing management program.

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