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ESI Africa asked the experts The Big Question: What are the technical, operational, maintenance, and financial considerations when extending the lifespan of a nuclear power plant?
Dr Derik Wolvaardt
Nuclear Engineering Specialist, Lesedi Nuclear Services, South Africa
As nuclear plants age and approach their end of design life conditions, utilities are embarking on plant life extension projects. This typically involves extending the life of plants from 40 to 60 years. These life extension projects involve hardware replacements and upgrades, as well as extensive safety and aging assessments that lead to oversight programmes needed to obtain the regulatory approval for extending the operating licence of the plant.
The main challenge that encompasses all plant life-extending efforts is regulatory approval. One of two approaches are generally adopted: In the US, utilities follow the prescriptive Nuclear Regulatory Commission’s License Renewal Rule (NEI 95-10). Outside of the US, utilities typically follow the IAEA Safety Aspects of LongTerm Operation (SALTO) approach. This approach is less prescriptive.
Due to their generic nature utilities must take important preparatory actions early to define and specify the process to be followed. Although the regulatory challenge is very important, it is the decisions and justifications made early on that determine the scope of the aging mitigation strategies.
From a technical perspective each safety-related system, structure or component (SSC) must be assessed for its ability to support an extended lifespan. Typically, up to a hundred thousand components may have to be analysed – such as safety-related pumps, valves, power cables, circuit breakers, civil structures etc. In order to make the task manageable, these components are screened and grouped based on similar material, environmental and other properties.
The condition of the reactor pressure vessel and the containment building is crucial. Should time-limited aging analyses show that these components cannot attain a life span beyond 40 years, then the plant is unlikely to have an economically feasible life extension. Other components, like the steam generators, turbines and various I&C systems, can be replaced or refurbished to achieve the extended operation.
Such a hardware renewal programme may have the greatest financial impact on the utility.
From an operation and maintenance point of view, an assessment of the adequacy of the plant’s aging management programmes is essential. Where inadequate or missing programmes are identified, these shortcomings must be resolved to assure the ongoing preservation of all nuclear safety functions.
Despite these challenges, facts presented at the 2019 WNA Symposium show that extending a plant’s life is considerably cheaper than building new plant, and that it is cost-competitive with both renewables and fossils fuels.
This article first appeared in ESI Africa Issue 1-2020.
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