FOCUS ON THE US | LIFE EXTENSION


be inspected for signs of reduced insulation resistance, radiation induced oxidation, moisture or debris intrusion or ohmic heating, as indicated by embrittlement, cracking, chipping, melting, discolouration or swelling.


Right:


Vistra Operations is hoping to extend the life of the Comanche Peak


reactors to 60 years


Absorbing operational experience A key process to manage aging effects in nuclear power plants is to make use of operational experience at the power plant and across the industry. Operational experience is used at Comanche Peak to


V manage age-related degradation or validating the effectiveness of any existing AMP for the period of extended operation.


● Internal surfaces in miscellaneous piping and ducting components. This AMP will manage loss of material, cracking, hardening and loss of strength and reduction of heat transfer using representative sampling and opportunistic visual inspections of the internal surfaces of metallic and elastomeric (including polymeric) components.


● Accessible power cables will be visually inspected for cable and connection jacket surface anomalies such as embrittlement, discoloration, cracking, melting, swelling or surface contamination that could indicate electrical insulation degradation. The first inspection for licence renewal will be completed prior to the period of extended operation and there will be recurring inspections performed at least once every 10 years thereafter.


● Internal portions of metal enclosed buses (bus enclosure assemblies) will be inspected for cracks, corrosion, foreign debris, excessive dust build-up and evidence of water intrusion. The bus electrical insulation material will


enhance existing programmes, prevent repeat events and prevent events that have occurred at other plants. To achieve this, plant personnel screen, evaluate and act on documents and information from outside sources to prevent or mitigate the consequences of similar events. The operator draws on external sources including Institute of Nuclear Power Operations (INPO) and NRC documents. Relevant foreign and domestic research and development programmes are also reviewed. Relevant research and development sources include: industry consensus standards development organisations; EPRI; communications issued by NRC staff based on research conducted by national labs used by the NRC; and nuclear vendor and owner’s groups. Experience, including that involving age-related


degradation, is tracked. Adverse trends are entered into the corrective action programme, as appropriate, for evaluation. If experience is identified as potentially involving aging it is evaluated with regard to systems, structures and components, materials, environments, aging effects and aging mechanisms. It will also be evaluated with regards to aging management programmes, which have an established performance feedback mechanism in place. In its application Vistra Operations said this process,


in conjunction with the corrective action programme, had proven to be effective in learning from adverse conditions and events, and improving programmes that address age-related degradation. However, to provide additional assurance that internal and external operating experience related to aging management is used effectively – including NRC and industry guidance documents and standards -


Abandoned engineering Any power plant in its fourth decade will have seen a number of its systems upgraded or replaced. In some cases the most suitable fate of the original system has been to remain in place, capped, closed or otherwise made safe for the remainder of the plant lifetime.


Comanche Peak has several such abandoned systems: ● The chemical feed system for steam generators in Unit 1 was removed from service when the new steam generators were installed. The remaining Unit 1 chemical feed recirculation components (pumps, piping, pipe supports and instrumentation) have been disconnected, capped and abandoned in place. The reverse osmosis system portion of the liquid waste processing system is not used at either unit at Comanche Peak and many of the systems’ associated components have been abandoned in place.


Also abandoned in place are: ● The jockey fire pump and diesel-driven fire pump ● Electric hydrogen recombiners ● A boron concentration measurement system ● A waste baling system in unit 1 that forms part of the solid waste management system. ● Portions of the potable and sanitary water system ● Some exhaust dampers considered to be part of the safeguards building ventilation system are abandoned in place in the open position.


Comanche Peak will enhance its programme to: ● Require the review of internal and external experience for aging-related degradation or impacts to aging management activities, to determine if improvements to aging management activities are warranted.


● Provide procedural guidance for identifying and reviewing experience. This will aim to identify aging that is in excess of what would be expected, relative to design, previous inspection experience and the inspection intervals.


● Establish coding for use in identification, trending, and communications of aging-related degradation.


● Establish guidelines for reporting plant-specific operational experience on age-related degradation and aging management to the industry.


● Provide training, on a periodic basis, to those responsible for AMP implementation and those responsible for reviewing, evaluating, and communicating operational experience items related to aging management and aging-related degradation.


This will begin as soon as renewed operating licences are issued and will continue throughout the remaining plant lifetime. ■


20 | December 2022 | www.neimagazine.com


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