lifespan of nuclear power plants
Koeberg nuclear power plant. Source: Bjorn Rudner

The Big Question we asked the experts is: What are the technical, operational, maintenance, and financial considerations when extending the lifespan of a nuclear power plant?

This article first appeared in ESI Africa Issue 1-2020.
Read the full digimag here or subscribe to receive a print copy here.

First, a word from the World Nuclear Association (WNA):

It should not be assumed that a nuclear power plant will close when its existing licence is due to expire, since operating licence extension is now common. Most nuclear power plants originally had a nominal design operating lifetime of 25 to 40 years. The latest engineering assessments have established that many can operate longer. However, significant capital expenditure is needed for the replacement of worn equipment and outdated control systems.

Prof Tariq Kahn
Head: Centre for Distributed Power and Electronics Systems, CPUT, South Africa

Many African countries are increasingly considering nuclear energy to diversify their energy mix. A world that is no longer going to be dependent on a large fossil fuel resource will face dramatic unplanned changes that would be impossible to manage. Both developed and developing (China, Japan, India and South Korea) countries have invested heavily in nuclear energy. A number of political, financial and economy based challenges remain in South Africa that will need to be addressed before expansion of our nuclear programme can be undertaken.

One of the most difficult problems associated with nuclear power is the disposal of waste produced during mining, fuel production, and reactor operation. The fundamental safety objective is to protect people and the environment from harmful effects of ionizing radiation, especially in the case of aging infrastructure. The need to systematically identify and address all environmental and safety concerns, and develop an Integrated Implementation Plan is foremost. A new environmental assessment (EA) process and an Integrated Safety Review (ISR) must be performed.

The ISR assess the plant design, condition, and operation according to the Periodic Safety Review of Nuclear Power Plants – Safety Guide (IAEA PSR Guide) published by the International Atomic Energy Agency (IAEA). New knowledge from R&D and advances in technology are taken into account. This enables determination of reasonable and practical modifications that should be made to systems, structures, and components, and to management arrangements, to enhance the safety of the old facility to a level approaching that of a modern power plant.

Non-compliance with modern standards and practices should be resolved. Concrete and water ingress, instrumentation upgrades and new control techniques will have to be assessed against the plant’s existing operational framework. Overall a costly exercise, but could be cheaper than a new build.

Israel Sekoko
Executive Chairperson, South African Young Nuclear Professionals Society, South Africa

Although the operating life of the majority of nuclear power plants originally ranged between 20 and 40 years, it is now fully accepted that the life of nuclear power plants can be increased to 60 years and more (i.e. up to 80 years). The cost benefits of extending the life of nuclear plants must outweigh the option of building additional power capacity (i.e. wholesale electricity sales must exceed the increased operating and maintenance costs from running the reactor for longer).

What makes life extension more attractive than new nuclear build is the cash-generated by an old power station because interest from its construction debt is already paid off.

Whereas new nuclear build reactors do not become significantly profitable until after they have reached their capital payback period.

There are practical examples and lessons learned from countries across the world that can easily be used by countries that are planning to extend the life of their nuclear plants (e.g. information from the International Generic Aging Lessons Learned (IGALL) programme).

Technically, long-term operations must focus on the components that are most critical to safety and hardest to replace (e.g. the reactor pressure vessel, reactor internals, large concrete civil structures, and the cable-supported nervous system of the plant) as replacing any of these components would most likely be cost-prohibitive and lead to plant closure. Aging is a significant factor in determining the limits of nuclear plant lifetime or life extensions. It is important to consider aging effects related to change in the physical properties; irradiation embrittlement; thermal embrittlement; creep; fatigue; corrosion; wear.

It is also critical for the utility to have a good understanding of the aging mechanisms so that appropriate programmes detailing when and how to inspect along with thorough evaluation of inspection results and good repair/replacement can be put in place.

Some regulators may require the operator to apply for a licence renewal before extending the life of the plant, whereas other regulators may follow a different process. The regulator will perform an extensive assessment and reviews of the safety documentation submitted by the operator before permission can be granted.

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. ESI

This article first appeared in ESI Africa Issue 1-2020.
Read the full digimag here or subscribe to receive a print copy here.