Nuclear Power in a Clean Energy Transition

Nuclear power today makes a significant contribution to electricity generation, providing 10% of global electricity supply in 2018. In advanced economies, one nuclear power accounts for 18% of generation and is the largest low-carbon source of electricity.

However, despite the growth of solar and wind power, the overall share of clean energy sources in total electricity supply in 2018, at 36%, was the same as it was 20 years earlier due to the decline in nuclear.

In order to achieve a trajectory consistent with sustainability targets – including international climate goals – the expansion of clean electricity would need to be three times faster than at present. It would require 85% of global electricity to come from clean sources by 2040, compared with just 36% today.

Nuclear power plants contribute to electricity security in multiple ways. Nuclear plants help to keep power grids stable. To a certain extent, they can adjust their operations to follow demand and supply shifts. As the share of variable renewables like wind and solar photovoltaics (PV) rises, the need for such services will increase. Nuclear plants can help limit the impacts from seasonal fluctuations in output from renewables and bolster energy security by reducing dependence on imported fuels. With nuclear power fading away, electricity systems become less flexible. Offsetting less nuclear power with more renewables would cost more and results in higher electricity prices for consumers.

Lifetime extensions of nuclear power plants

The average age of their nuclear fleets is 35 years. The European Union and the United States have the largest active nuclear fleets (over 100 gigawatts each). They are also among the oldest. The average reactor is 35 years old in the European Union and 39 years old in the United States. The original design lifetime for operations was 40 years in most cases. One-quarter of the current nuclear capacity is set to be shut down by 2025 – because of policies to reduce nuclear role.

The European Union sees the largest decline in capacity in absolute terms, at over 100 GW. So, of the 126 reactors in operation, 89 will be decommissioned by 2030 without further extensions. By 2040, just 15 of the existing reactors will be in operation, complemented by four reactors that are under construction.

To pursue, lifetime extensions are considerably cheaper than new construction and are generally cost-competitive with other electricity generation technologies, including new wind and solar projects. However, they still need significant investment to replace and refurbish key components that enable plants to continue operating safely. But markets and regulatory systems often penalize nuclear power by not pricing in its value as a clean energy source and its contribution to electricity security and this make the difference between a lifetime extension and a shut-down.

Nuclear power plant
Nuclear Power Plant

New nuclear construction

The biggest barrier to new nuclear construction is mobilizing investment. Plans to build new nuclear plants face concerns about competitiveness with other power generation technologies and the very large size of nuclear projects that require billions of dollars in upfront investment. It has become increasingly clear that the construction of a new wave of large-scale Generation III reactors in all European or North American electricity markets is inconceivable without strong government intervention. The cost of capital has a pronounced impact on the economics of new nuclear power projects because of the size of the required investment and long project lead-times.

Small Modular Reactors

The difficulties faced in building large nuclear plants and the evolving needs of the power system have generated interest in advanced nuclear technologies that are amenable to smaller plants, including SMRs.

SMRs are nuclear reactors with an electrical capacity of less 300 MW per module. They are usually designed to be built in a factory to take advantage of economies of series and then transported to the site where they are to be installed. SMRs exploit inherent safety features, such as passive safety systems and simplified designs, involving fewer and simpler systems and components. They will be deployed in series, using a global supply chain to lower costs.

Small modular reactor - Wikipedia

How does Small Modular Reactors (SMRs) work ?

  • Nuclear power plants produce heat through nuclear fission

The process begins in the reactor core. The Atoms are split apart – releasing energy in order to produce heat as they separate into smaller ones.

  • Insertion of control rods made of neutron-absorbing material into to the core

Regulation of the amount of heat generated by the chain reaction

  • Reactor coolant water picks up heat from the reactor core

Conversion of water in a secondary loop into steam

  • Steam used to drive a turbine

Generation of electricity

  • Pressurizer keeps the reactor coolant water under high pressure

Prevents it from boiling

To sum up, SMRs could be installed as single modules distributed throughout the grid, which may be attractive in countries or regions with less developed networks, in remote regions or as dedicated sources of electricity for industrial complexes, as well as in more traditional large-scale plans by grouping together several modules. In principle, SMRs could be suitable to meet the needs for flexibility in power generation demanded by the electricity systems of the future that combine baseload with increased shares of variable generation.


Nuclear Power in a Clean Energy System, iea, May 2019.


About the author

Francesco Poggi
Senior Mechanical Engineer at ENGIBEX

Francesco Poggi
Senior Mechanical Engineer

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