Planning for long-term nuclear plant operations22 April 2020
More than half of the world’s nuclear power plants are expected to pursue operating licence extension. Andre Zander looks at how plants can evaluate and prepare for long-term operations.
THE COST OF INVESTING TO extend the life of an existing nuclear power plant is typically lower than the cost alternate sources of energy generation or of building new power plants. At the same time, there is a growing recognition that the continued operation of existing nuclear power plants is vital to achieving global CO2 reduction targets.
To renew its licence a plant owner must provide its national regulator with an assessment of the technical aspects of plant ageing and show how any issues will be safely managed. This includes reviewing metals, welds and piping, concrete, electrical cables and reactor pressure vessels.
In the US, the Nuclear Regulatory Commission issues licences for nuclear power plants to operate for up to 40 years and allows licences to be renewed for a further 20 years with every renewal application, as long as operators prove that the effects of ageing on plant structures and components will be adequately managed.
For nuclear power plants, life extension must be based on evidence that the plant will comply with the licensing basis over the extended period of service. How this is achieved will depend on regulatory strategies in different countries. In general, it requires an assessment of the current and projected condition of the plant and of the fundamental safety systems to ensure that these systems will continue to perform their functions during the extended operating period. The strategy may address the impact of ageing, or seek changes in safety levels based on the expectations for newer plants.
The technical lifetime of a nuclear power plant is limited by the cost of investment to fulfil the ongoing licensing procedure or framework that aims to meet national and international nuclear safety standards. By applying good asset management and performing a specific, ageing-related safety assessment, nuclear plants can operate beyond their assumed design life without decreasing the safety and availability of the unit, while reducing its maintenance and operating costs.
Evaluating long-term operations
The economic assessment of life extension should consider factors reflecting the current and future financial conditions of operation, political and regulatory uncertainties, the state of the plant’s equipment and the general role of nuclear in the country’s energy policy. The Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency Ad Hoc Expert Group on the Economics of Long-Term Operation of Nuclear Power Plants identified the following criteria as appropriate for assessing such programmes:
- the production and asset portfolio;
- predictability of future electricity prices;
- equipment upgrade and replacement needs;
- the impact of refurbishment activities on the average energy availability factor;
- risk and uncertainty (site-dependence, political, financial and regulatory);
- the overnight cost of refurbishment;
- levelised cost of electricity generation after life extension activities; and
- the country’s carbon policy and security of energy supply.
Life extension is, in general, economically beneficial, compared with other options. It requires less capital investment, with less risks for investors and ultimately lower costs for consumers.
One of the fundamental lessons learned is the importance of reviewing a plant’s existing ageing management programme to ensure the availability of safety functions throughout the extended service life and to confirm that the programme meets international requirements. These requirements are demanding and require a sound knowledge base for the periodic evaluation of degradation in systems, structures and components.
This requirement is being undertaken at South Africa’s Koeberg plant, which has been in commercial operation since July 1984 and is now intended to operate beyond its design life of 40 years.
Previous programmes also demonstrated that it is important to use proven methodologies to manage the life of plant components and to optimise plant safety, availability, reliability and operating costs, including maintenance rules for active components and environmental qualification of electrical and I&C equipment. Access to engineering and expert consultancy in ageing and plant life management for mechanical equipment, electrical and instrumentation and control (I&C) components, and civil structures is helpful.
To support life extension activities, Framatome developed an integrated software platform called COMSY, designed to manage ageing issues and life cycle management activities. The software platform comprises functions for all mechanical components, electrical, I&C system, civil structures, and monitoring and diagnostic applications.
Developing a long-term operations plan
An integrated life extension plan maps out the physical configuration and economic goals for a reactor unit and includes an ageing management plan, with timing and funding of specific actions.
It is also an opportunity to consider the actions required for a future power or efficiency uprate. That could be the key to demonstrating the necessary return on investment. The overall objective is to ensure that ageing management- related programmes are in place monitor and manage ageing effects with preventive or mitigation measures for the intended period of operation. It must:
- identify plant systems, structures and equipment considered safety-relevant (scoping);
- define commodity groups (screening) and evaluate them as regards potential degradation;
- identify lifetime limitations by design and evaluate continued acceptability;
- validate existing plant programmes and ensure that preventive actions are in place to manage ageing effects.
- Integration of ageing management into planning and preparation allows inspection and maintenance to be optimised while:
- maintaining a high level of safety;
- optimising the operation, maintenance and service life of systems, structures and components;
- maintaining performance levels;
- maximising return on investment over the service life; and
- creating the best conditions for life extension.
The programme scoping and ageing management techniques focus on selecting passive and long-lived structures, components and systems for ageing analysis. Among the obvious selections are those that are safety- related, as well as conventional systems in need of upgrades or refurbishments. History and ageing data are collected to allow for economic analysis with regard to long- term business objectives.
A life extension plan also presents an opportunity to consider flexible operation. This may require additional investment, but plant upgrades can enable any nuclear power plant to become more flexible in operation. It depends on grid demand, flexible operation capabilities and how they align with system needs, and implementing any upgrades. These could include an advanced load- following control system PWRs, which ensures automates load-following operation without manual intervention.
Fatigue caused by load-following operation can affect the cumulated usage factor (CUF). The plan should include optimisation of operation modes enabling CUF minimisation.
Up to 20 nuclear power plants per year are expected to review their operating licences between now and 2025. A life extension plan helps to facilitate this process, and chart the path forward for continued efficient, reliable, safe and carbon-free electricity generation.
Author information: Andre Zander, Framatome expert in ageing and plant life management
Above Image: Koeberg nuclear plant in South Africa (Credit: Framatome)