Verónica Castro-AllendeSmall Modular Reactors (SMRs) present a promising solution for Sweden’s growing electricity demands, offering a smaller, more flexible alternative to traditional nuclear reactors. Developed within the ANItA project, SMR designs are poised to increase Sweden’s nuclear capacity. These reactors have multiple applications, from electricity generation and district heating to hydrogen production. The SMR designs identified for Sweden include innovative features such as passive safety, novel reactor containment designs, and boron-free water chemistry, all of which simplify reactor construction and operation. Unlike traditional light-water reactors, SMRs can be rapidly constructed using prefabricated modules and offer the advantage of dry storage for nuclear waste, reducing the need for expansive wet-storage facilities. However, further research is essential to address the licensing, operational, and financial challenges posed by these novel technologies. Understanding these innovations and the technical, legal, and economic obstacles is crucial for SMRs to be successfully deployed across Sweden. As ANItA continues its investigations, Sweden moves closer to embracing this next generation of nuclear power technology, contributing to a sustainable energy future.
Small Modular Reactors designs that are ideal for Sweden’s electricity production are identified in the work carried out within the ANItA project, which also highlights the need for additional research.
One of the ongoing initial projects at the Swedish national competence center for nuclear power technology, ANItA, is the identification of small modular nuclear reactor ( SMR ) designs that are appropriate for Sweden’s relatively soon-to-be-achieved electricity generation. The aim is, however, to point out novelties compared with the recent Swedish reactor fleet that might need more investigation.
Ideal SMR designs
SMRs are regarded as a potential way to increase Sweden’s radioactive capacity. The SMRs can be used for various purposes. The heat generated can be used for district heating to heat homes and industrial buildings as well as for electricity generation, as well as for hydrogen production. Within ANItA, all of these applications are being investigated.
SMRs of different types have been suggested, some based on the technology of the present nuclear reactors and others designed for use in the upcoming Generation IV atomic power systems. Generation II I + reactors are typically classified as the types based on the technology of existing nuclear reactors. IAEA has compiled design descriptions for some, but not all, proposed SMRs. ¹
As the name suggests, SMRs differ from large-scale reactors in that they are smaller and more flexible. This results in smaller real dimensions, lower power output, and a greater use of prefabricated modules that will be assembled at the reactor construction site. These features imply possible advantages over large-scale reactors. Reactors that are easier to design and operate generally result in smaller size and output that are easier to use for purposes other than producing electricity. Notably, the increased modularity even allows for shorter construction times.
There are now six functional large-scale reactors in Sweden, and six completely shut down. All of these started operating between 1972 and 1985, and they are of the type light-water reactor, which means that they use light water ( i .e., regular water ) as the coolant and to reduce the neutron energy released during the fission process that is taking place in the nuclear fuel. The term light-water reactors is used to distinguish them from heavy-water reactors, which use heavy water instead ( i. e. water enriched in the hydrogen isotope deuterium ).
There are two main varieties of light-water reactors: boiling water reactors ( BWRs ) and pressurised water reactors ( PWRs ), both of these are used in Sweden. The most widely used reactor technology is light-water, not just in Sweden but also all over the world.
As the legislation in Sweden is adapted to land-based ( as opposed to marine-based ) light-water reactors, it will, from a licensing perspective, be less of an effort to deploy this type of SMR compared with other types. Secondly, to be easily transportable, the design needs to be at an advanced stage. Additionally, the SMR should be created by a company with the ability to deliver the reactor and that is based in a nation where atomic technology is socially acceptable.
More than 25 land-based light-water SMR designs have been proposed. One BWR and four PWRs are used as reference designs in the research carried out for this project. The five SMRs are ( with the developing organization inserted into parentheses ):
1. BWRX-300 ( GE-Hitachi )
2. Rolls-Royce SMR ( Rolls-Royce )
3. AP300TM ( Westinghouse )
4. VOYGRTM ( NuScale )
5. NUWARDTM ( EDF)
Novelties in proposed SMR designs
In contrast to the current and past Swedish reactors, the proposed light-water SMR designs have a number of significant novel features. Some of these features are fascinating to the world, while others are used in various reactors outside of Sweden. Some of the innovations are anticipated to result in simpler reactor construction or operation. However, it is important that the novelties are well understood from a professional standpoint and that there are no legal repercussions for implementing them before they can be used in a genuine reactor.
Aside from the smaller size and increased flexible construction, the proposed SMR designs have some significant novel characteristics in comparison to the present and past Swedish reactors:
• Enhanced use of organic circulation
• Increased silent safety
• Novel reactor containment designs
• Integral PWR designs
• Novel types of water chemistry
• Having various reactors housed in a typical reactor building and controlled from a typical control room
• Increased load-following capability
• Dry storage of used radioactive fuel
No pumps are used to circulate the reactor coolant, which is achieved by normal circulation. With fewer components and less maintenance required, it is possible to design and operate a reactor more effectively. Secondly, it allows for increased safety, not relying on the pumps.
Passive safety, for that no operator action, additional supply of electricity, or other ancillary systems are needed to keep the reactor core cooled for three days or more, is implemented in the SMR designs. Passive safety is, to a big extent, enabled by the use of healthy circulation. Gravity and pressurized systems are additional features that enable silent safety.
A structure called a reactor containment serves the purpose of containing radioactivity in the event of an accident. While the SMR designs have containments made of steel or steel–concrete fiberglass materials, all Scandinavian reactors have containments made of pre-stressed concrete, unlike the SMR designs.
In integral PWR designs, some of the major components, e. g., steam generators, drive mechanisms for control rods, and pressuriser, are located inside the reactor pressure vessel. The reactor is intended to be delivered as a single unit that is connected to the non-nuclear parts of the power plant because internal PWRs are significantly smaller than typical PWRs.
The proposed use of boron-free PWR coolant in some SMRs is the most significant innovation in water chemistry. Boron is used in recent PWRs to control the reactivity, i. e., the rate of the fission process. Other novel forms of water chemistry are likewise suggested. To minimize material degradation, water chemistry needs to be optimized. This is necessary for the long-term operation of the reactors.
From the perspective of both construction and operation, having numerous small reactors housed in a single common building that are operated from a single common control room is effective. With fewer staff members, it is possible to run the reactors.
The ability to adjust the grid’s electronic output based on the need for electricity is known as load-following capability. To some extent, this flexibility currently exists in recent reactors. There are two main ways to reduce load-following: one is to lower the reactor’s power when the demand for electricity falls, and the other is to keep the reactor running at full power. For example, using the steam to produce hydrogen or heat another industrial processes would be beneficial.
The interim storage facility Clab in Oskarshamn houses the used nuclear fuel in Sweden in water pools ( so-called wet storage ). When is done in many other countries, some SMR designs allow for clean storage of used fuel at the reactor site. The introduction of dried storage in Sweden has two main advantages. Firstly, once its capacity is reached, there wo n’t need to expand or construct a new wet-storage facility. Second, transportation of spent nuclear fuel will be less frequent. This might be advantageous if SMRs are deployed at novel locations without maritime connections, which would be helpful.
Need for further investigation
Novel features can affect one or more of radioactive reactor licensing, construction, and operation. The maintenance of the reactor components and the disposal of nuclear waste are both regarded as essential components of the reactor’s operation.
The licensing and operation of the SMRs may be impacted by all of the novelties listed below, as well as the smaller size and the more modularity. The smaller size, the more modular design, and the new containment designs will also have an impact on the power plants ‘ construction.
It is crucial to address the possible obstacles that the novel features may present in order to effectively deploy SMRs in Sweden. The novelties must be properly understood, their functionality demonstrated, and permitted. Therefore, more investigation is required regarding both the legal framework and the technical aspects of atomic power. Moreover, the financial aspects of SMRs need to be considered. Another ANItA projects are currently being conducted, and some of the novelties and the related potential obstacles are the subjects of their discussions. In upcoming ANItA projects, additional topics are anticipated to be investigated.
Summary and conclusions
SMRs are one way to increase nuclear capacity in order to meet Sweden’s coming electricity demand. Of the numerous SMR types proposed, light-water SMRs, i. e. reactors similar to but smaller and more flexible than existing large-scale reactors, are the most likely to be built in the reasonably near future. Because of their similarities with existing reactors, the proposed light-water SMRs should, for the most part, be quite easy to license, construct, and operate. However, the proposed SMR designs have some tale technical elements that need to be investigated more in order for their successful deployment and operation in Sweden.
