When a country is deciding on whether it should implement anew nuclear power programme, or expand an existing one, it will need to consider which type of reactor to acquire. Much like any consumer choice, there are a number of factors which come into play.
Questions need to be asked such as how much will it cost; is the vendor offering a finance deal; what is its reliability; what is its power output; what is the guarantee period?
Another factor to take into account is its size.
You wouldn’t buy a large car if you lived somewhere with a poor road infrastructure. Equally, a large reactor is no good if the electrical grid capacity isn’t there to support it. So what would the choice of reactor be if that were the case?
Some countries are exploring the use of so called SmallModular Reactors (SMRs) which are defined (by the IAEA) as advanced reactors that produce up to 300 MW(e). 
By way of comparison, the UK’s new Hinkley Point C twin-reactorEPR will generate 3,260 MW(e), enough electricity to supply six million homes. Rolls-Royce is developing a 440 MW(e) SMR design (although a “medium” sized reactor in IAEA terminology) which will “supply a city the size of Leeds”.
What are SMRs?
As mentioned, SMRs are defined as advanced reactors that produce less than 300 MW(e). There are many current designs that fall into the less than 300 MW(e) capacity, including many of the UK’s now defunct Magnox reactors, but they wouldn’t be classed as SMRs. So what is special about them?
The key is the use of the term “advanced”, which describes features such as integrated design (which dispenses with the need for large coolant piping), modularity of manufacture and installation, passive safety (meaning fewer moving parts that can go wrong and a reliance on natural circulation of the coolant if something does), underground containment (sometimes) and reduced nuclear fuel requirements.
Are they ready for market?
There are about 50 SMR designs under development globally, with four under construction in Argentina, Russia and China.
Most designs fall into four broad types: water cooled land based, water cooled marine based (floating), high temperature gas cooled, fast neutron and molten salt. A description of these can be found in the IAEA 2018 publication, Advances in Small Modular Reactor Technology Developments.
There is currently additional SMR activity in the following countries:
UK: Rolls-Royce has a target date of 2029 for the commissioning of its design (according to a recent statement from its chief technology officer); this would be at a cost of £1.75b.
Ukraine: NuScale has just signed an agreement with Ukraine’s State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS) for the implementation of its 60 MW(e) design.
Saudi Arabia: The government of South Korea and the King Abdullah City for Atomic and Renewable Energy (KACARE) have signed an updated agreement to create a joint venture for the construction of a low-power SMR in Saudi Arabia.
United States: In December 2019 Oklo Inc. received permission to construct its 1.5 MW(e) “Aurora Advanced Fission Clean Energy Plant” at Idaho National Lan (INL). Also, the Tennessee Valley Authority (TVA) obtained approval in the form of an Early Site Permit (ESP) for the potential construction of up to 800 MW(e) SMR capacity utilising four SMR designs. Design reviews by the US Nuclear Regulatory Commission (USNRC) are being progressed for the NuScale SMR, and together with the Canadian Nuclear Safety Commission they are reviewing the Terrestrial Energy’s Integral Molten Salt Reactor (IMSR®).
Poland and Estonia are both looking to deploy GE Hitachi SMRs.
What are the benefits over larger scale reactors?
In order to maintain grid stability, the practical limit to the maximum capacity of any single generating unit is around 10% of the minimum electrical demand of the country. For countries with a small grid capacity, an SMR thus presents an ideal solution over a larger reactor design.
A further benefit is the ability to deploy them in remote locations which may have no national grid connections at all. As they are generally designed to be load-following they can cope with variable electricity demand, unlike the larger units which are very good for base load supply.
In terms of physical size, they are small, and some can even be transported on the back of a truck or by barge. The Russians connected their first floating nuclear heat and power plant (FNHPP) to the grid in December 2019, into the isolated network of the Chauny-Bilibino hub in the Far East.
The modularity aspect means they can be manufactured in modules in factories and assembled at site, and so will benefit from economies of volume production. This also means that second or more units can be built at the same location as demand increases.
From a financial perspective, which we will look at in more detail in the next article, building a first reactor can generate revenue which can then finance a second reactor, and so on.
What can SMRs be used for?
As well as the obvious generation of electricity to supply to a local community, SMRs have a number of non-electricity generation capabilities. These include district heating supply (see here for an example project in Finland), seawater desalination and various oil and gas applications, such as methanol and hydrogen production.
What are their disadvantages?
Although four units are under construction, any new deployment not involving those designs would be the first of a kind. This has disadvantages, of course, in that it will essentially be a test bed for the next of a kind, so that the full benefits may not be achieved for some time.
As with any nuclear facility, the question always arises as to the management of operational radioactive waste, management of the spent nuclear fuel and the SMR’s ultimate decommissioning and disposal at the end of its life. In order to use existing or planned disposal routes, SMRs must not produce novel waste forms that may compromise the safety case for an existing disposal facility.
Although this is unlikely to happen, a bigger question is what to do with the spent nuclear fuel. Should this be directly disposed of or reprocessed? If reprocessed, where should the disposal facility be? Should it be in the country of origin or the country of deployment? In the case of the latter, there may not be the infrastructure or even the geology.
In two further follow-up articles we will look at other aspects of this growing market, including the financial, contractual, infrastructure, regulatory and legal aspects of deploying SMRs.
 New nuclear power plants are currently under construction or planned in countries including China, USA, UK, UAE and Finland. These are “conventional” large scale units of between 1000 and 2000 MW(e).