What are small modular reactors and what makes them different?

There has been considerable public discussion about small modular reactors as the newest, most innovative and versatile nuclear power solution that many countries around the world are interested in adopting.

Given the Federal, New South Wales, and Victorian government inquiries into matters relating to the feasibility of introducing nuclear power into Australia and the prospects for expanded uranium exploration and mining activities, as well as challenges related to the need to reduce carbon emissions, it is important that Australians are kept abreast of global developments in nuclear power technologies.

So, what are small modular reactors, or SMRs? The term refers to a class of modern reactors that are essentially “small”, and each unit can be manufactured in a factory.

They are “modular” in the sense that each unit can be assembled next to another and scaled up or down to meet the local electricity needs.

They are also designed to “plug in” to existing power networks and therefore can essentially replace an aging power station with a modern, reliable, and zero-emissions power source.  

SMRs differ from today’s more common nuclear power reactors in a few important ways:

First, their holistic approach to manufacturing occurs through design simplification. Compared to the complex design and construction of currently operating large-scale reactors, simplification opens up the prospect of assembly-line manufacturing of pre-fabricated modules—providing economies of scale.

As the majority of construction takes place off-site, building small modular reactors takes less time.  An SMR has a projected construction time of three to five years, while a large reactor takes six to 12 years.

And it is possible to construct a reactor with a single module or use units in combination for greater power output. Additional modular units can be added and brought online incrementally for greater power output.

Secondly, SMRs are designed with a high level of passive or inherent safety features. This means operator intervention or external power supply are not needed to shut down the reactor and maintain cooling to remove the core’s residual heat in the event that power is lost to the plant.

The geographic footprint of nuclear power plants is very small compared with other sources, including hydropower, solar, and wind plants. Small modular reactors will require an even smaller footprint than the large reactor sites that are in existence around the world.

Thirdly, “Unlike large reactors, which require an exclusion zone, US regulators have decided that some SMR designs there can have the Emergency Planning Zone, or EPZ, shrunk to the plant’s site boundary,” explains Dr Mark Ho, an expert on nuclear reactors in ANSTO’s Nuclear Analysis Section.

The EPZ is area surrounding the nuclear power plant within which special considerations and management practices are pre-planned in case of an emergency.

Conventional plants have a 16-kilometre radius for emergency planning, with a wider exclusion zone of up to 80 kilometres to protect food and water sources.

Choosing a site for a nuclear reactor involves assessments of health, safety, and security; engineering needs and costs; as well as socio-economic and environmental considerations.  

For a variety of reasons relating to their design and small geographic footprint, SMRs offer greater flexibility in the choice of a site than large reactors.

SMRs use only a small amount of fuel and refuel approximately every two years. They also do not require newly developed reactor fuels, such as accident tolerant fuels with advanced safety characteristics.

SMRs can run on standard reactor fuel because of their passive safety systems that make the reactor ‘walk away safe’.

There are a number of options to enhance proliferation resistance and ensure safeguards of fuels used in the new SMRs. The International Atomic Energy Agency has a publication which explores these considerations.

A smaller reactor core is also advantageous, as it is easier to cool during operation and after shutdown.

For some designs, a reservoir of water sits above the reactor core, which is similar to the design of Australia’s  OPAL multi-purpose research reactor located in Sydney on the ANSTO campus. It doesn’t totally remove the need for an external water source, but these reactors do not need to be sited on the coast or next to a river.

Another feature of the technology in delivering power is its compatibility with the existing electricity grid.

SMRs could be used to bring energy to locations at the furthest extent of the grid.

Their operation would be expected to enhance reliability of the grid and secure supply, especially when renewables are part of the energy mix.

Many billions of dollars in investment have gone into the design of SMRs, and much of the recent progress has been made possible by private venture capital and some overseas government investment.

Countries including the United Kingdom, the United States, Canada, China, and India, among others, have reinvigorated public and private investment in SMR R&D projects, with the Canadian government, in particular, providing support for the creation of an SMR technology demonstration park.

American company, NuScale Power, has designed a new type of power plant that uses heat coil steam generators without the use of reactor coolant pumps. The system has a small, efficient core, within a high-strength steel containment vessel that requires no power for shutdown or cooling. NuScale expects to have its first SMR operating by 2026.

Another company, Terra Power, which is backed by Bill Gates, is developing several innovative SMR technologies for potential use in providing electricity to the developing world. The designs use new technologies that reduce the need for new uranium mining and used fuel storage facilities, among other advantages.

Although there are uncertainties and complexities in estimating the financial implications, the cost of building a small modular reactor has been estimated at $US 1 billion compared to $US 6 billion for a large 1 GWe reactor.

“What is clear is that the economies of scale it offers are bringing down the price per kilowatt-hour of capacity significantly,” said Ho.

In explorations of nuclear power options, the question sometimes arises as to whether Australia has the nuclear expertise to introduce nuclear technologies for power applications if the country ever were minded to repeal existing prohibitions.

“Because of ANSTO’s expertise in nuclear in operating Australia’s only multi-purpose research reactor and our close association with countries with nuclear expertise, there would be time to acquire the knowledge and to develop the training programs in preparation for a nuclear industry, if the Australian Government ever were to make that decision,” said Ho.

As the country explores future energy options, more discussion of SMRs is likely to take place.