Prospects for small reactors

28 April 2021

NEI speaks with Hadid M. Subki, Nuclear Engineer, SMR Technology Development, within the IAEA’s Department of Nuclear Energy.

MORE THAN 70 DIFFERENT SMR designs are described in the International Atomic Energy Agency’s new booklet, Advances in SMR Technology Development. Of those, one has been recently put in operation – Russia’s floating NPP with KLT-40S reactors. The HTR-PM in China is nearing commissioning and Argentina’s CAREM-25 is approaching prototype operation.

What factors influenced the successful development and deployment of these examples?

A variety of factors will contribute to the successful development and deployment of small modular reactors. Countries need to implement strategic national programmes on the design and the technology development of advanced nuclear reactors.

This should include a steady budget flow to fund technology development. Furthermore, stringent regulatory reviews and licencing, and a robust supply chain for the manufacturing of components, construction and operation are essential.

Water-cooled designs are by far the largest category, with 31 designs including six for marine use, and HTRs are the second largest group with 14 designs. How do you assess the prospects for these two technologies?

The industry has decades of experience with water- cooled reactors in large nuclear power plants and nuclear icebreakers. Therefore, technology development for small water-cooled land-based reactors is less challenging because they will be based on either licensed designs or operating reactors.

High temperature reactor (HTR) technology is not far behind water-cooled reactors in terms of deployment readiness. HTRs have several technical advantages including higher efficiency for electricity generation, inherent safety features such as accident-tolerant fuel, cladding providing containment and reactor cores designed in ways that the probability of a meltdown ever happening is extremely low even in most hypothetical scenarios. HTRs are also highly efficient in providing nuclear heat for hydrogen production.

Both small modular reactor (SMR) concepts show tangible progress. Argentina and the Russian Federation are advanced on water-cooled SMR. China, where the HTR- PM is in the hot testing phase, is leading in developing HTR technology.

The study shows only seven designs deployed by 2030. Apart from China’s HTR-PM, these are all water-cooled designs. Could you comment on this?

According to the IAEA’s booklet, Advances in SMR Technology Development, a preliminary study taking into account vendors’ design information, there might be no fewer than a dozen SMR designs ready to start operations by 2030, for a total installed capacity of about 1600MWe.

These designs include both water cooled and non-water cooled designs, including HTR designs.

Water is an excellent material for both reactor coolant and moderator, so the industry has a long experience in operating water-cooled reactors. This long operation record reinforced the readiness of manufacturing facilities, test facilities and regulations, for water-cooled reactors.

Several other designs, such as molten-salt fuelled reactors, other liquid-metal cooled fast reactors and heat pipe cooled technology for microreactors, are currently at the stage of pre licensing activities. The goal is to deploy them by 2030. Construction of a 300MW lead-cooled reactor, intended as a demonstration plant for a future bigger model, is being prepared in Russia for a target operation date around 2026.

Of the total, around 40 are still in the conceptual design stage. Do you expect many of these to reach the final design stage by 2030?

Several designs are in pre-licensing stages with regulators, and some are likely to achieve their target start of operation by 2030.

As competition for funding is fierce, even water-cooled reactor designs with familiar technology have experienced delays in entering the market for various reasons.

Many factors affect deployment readiness. First, the vendor’s target deployment date, which may sometimes be optimistic; second, whether or not licensing engagement for the design is taking place; third, how many utilities, countries or users are interested in deploying the design within a certain time frame; and last but of key importance, government and private sector support in funding, development, licensing and deployment of the first-of-a- kind unit.

In the nuclear industry, development activities are always accompanied by a series of verification and validation tests and a stringent quality assurance framework, which require additional time and resources.

The 2020 IAEA booklet on SMRs for the first time includes a dedicated section on microreactors. What are the advantages of these designs? Why are they gaining in popularity?

As a subset of SMRs, microreactors are advanced reactors typically designed to produce up to 10MWe, to generate electricity and heat for sites and applications where higher power would not be feasible or needed.

This technology can penetrate new markets for nuclear energy with small, distributed, yet continuous electric energy demand. Their advantages include a relatively small energy output, suitable for mining in remote areas, off-grid areas and small islands, where they could help replace carbon-intensive diesel power generation.

With low power output, a long core lifetime, lower source term and design simplicity, microreactors are designed to be compact for transport, fast fabrication and installation. They could be used for hydrogen production, water desalination, refining and petrochemical production.

Microreactors would also have substantially lower upfront capital cost, compared to the higher power SMR designs, a fact that may have enhanced their recent popularity.

Apart from power production, some SMR designs are also proposed for other industrial uses such as hydrogen production – in particular, some HTR and fast reactor designs. Could you elaborate on this? Any nuclear reactor can be the platform for hydrogen production without emitting greenhouse gases and other pollutants. Existing PWRs or BWRs can produce hydrogen through conventional electrolysis of water.

One promising technology for hydrogen production is the HTGR, including its Gen-IV design, the Very High Temperature Reactor (VHTR). The first fleet of HTGRs may be deployed after the next decade. Their coolant outlet temperatures of 750-1000°C can provide pathways for massive hydrogen production.

Projects in Japan and the USA are currently developing new hydrogen production techniques that might soon be operational. So, in the near term with cogeneration, SMRs may be competitive with hydrogen generation from variable renewables and could help reduce the need for fossil power plants in producing hydrogen.

Currently, there is strong interest in SMRs for immediate hydrogen production, in competition with methane reforming powered either by fossil fuels using carbon capture and storage (CCS) or variable renewables such as solar and wind. Eventually, SMR-produced hydrogen could be among the most cost-effective methods, in addition to being carbon-free. Support for strategic development, experiment and testing, and demonstration plants are needed at this stage.

The 70+ designs include a range of different fuel types. To what extent is fuel development a factor affecting the progress of these designs?

Innovative fuel development for SMR has a different impact depending on the reactor design.

For immediate deployment of PWR technology, most designs use shorter versions of proven standard fuel assemblies used in existing large advanced LWRs. For these, some thermal-hydraulic confirmatory tests will be required, but there is no need for advanced R&D. However, R&D is being carried out on fuels with increased accident tolerance for this reactor type and also on how to optimize the refuelling interval, as this is an effective means to enhance economic efficiency.

In contrast, innovative non-water-cooled reactors using the fast neutron spectrum or other technologies will generally require brand new fuel assembly designs which take years to develop, test and make ready for use in the core.

If the demand for SMRs increases in coming years, what are the prospects for serial production of the reactors?

Up to 2030 the industry will present first-of-a-kind designs of SMRs. Tangible numbers of orders, for serial production, might be placed towards the end of this decade or in the beginning of the 2030s.

The expected game changer for SMRs is the mass production of modularised systems, components and structures in a factory, as in aviation. If realised, this will have a positive impact on reducing costs and timelines for deployment.

Serial production depends on the continuity of orders for, and capacity of, existing nuclear component manufacturers. To realize the economic benefits of mass production, it might be necessary to develop a small number of market-ready standardised designs through international cooperation.

SMRs, as a prospective nuclear energy source, must be proven to be economically affordable and competitive. They could also provide solutions where no real alternative exists, such as the deployment of microreactors in off-grid remote regions that require no refuelling interval.

The Akademik Lomonosov floating power plant. This is the only SMR of more than seventy described in the IAEA’s new report to have entered operation (Photo: Rosatom)
HTR-PM pebble bed fuel (Source: CNNC/ China-Huaneng)
HTR-PM plant (Source: CNNC/ China-Huaneng)
Control room during hot functional testing (Source: CNNC/ China-Huaneng)

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