Small modular reactors (SMRs) are nuclear fission reactors that are smaller than conventional reactors. The term “small” in the context of SMRs refers to design power output. As per the International Atomic Energy Association (IAEA) classification, small modular reactors are defined as reactors that produce a power output of less than or equal to 300 MWe. It must be noted that most of the commercial reactors operating around the world are large reactors with power output ranging between 1000 MWe and 1600 MWe. The term “modular” in SMRs refers to its scalability and the ability to fabricate major components of the nuclear steam supply system (NSSS) in a factory environment and then transport them to the site. Its scalability means that some SMRs are to be deployed as multiple-module power plants.
SMR designs include:
- Light Water Reactors
- High-Temperature Gas-Cooled Reactors
- Liquid Metal Cooled Reactors
According to their promoters, the scalability, modularity, robust design, and enhanced safety features of the SMR offer great advantages over large commercial reactors. It must be noted that this reactor design is currently (2018) at the stage of development. However, its technology is similar to proven naval reactors.
SMRs have the potential to expand countries to enhance the energy supply security and embarking countries which have inadequate infrastructure or less established grid systems (not suited for large commercial reactors). However, SMRs have the potential to become a key part of the energy mix even in developed countries that often face problems with the construction of large commercial reactors.
See more: ADVANCES IN SMALL MODULAR REACTOR TECHNOLOGY DEVELOPMENTS, a supplement to ARIS, IAEA, 2014.
Advantages and Disadvantages of Small Modular Reactors
Small modular reactors are very specific. Their size and modularity offer many advantages. On the other hand, they have some disadvantages, which must be considered during decision-making.
Enhanced safety and security
Lower thermal power of the reactor core, compact architecture, and employment of passive concepts have the potential for enhanced safety and security compared to earlier designs and large commercial reactors. The passive safety systems are a very important safety feature in the SMR. Therefore, there is less reliance on active safety systems and additional pumps and AC power for accident mitigation. These passive safety systems can dissipate heat even after the loss of offsite power. The safety system incorporates an on-site water inventory that operates on natural forces (e.g., natural circulation). In reactor engineering, natural circulation is a very desired phenomenon since it can provide reactor core cooling without coolant pumps so that no moving parts could break down.
As was written, the term “modular” in SMRs refers to its scalability and the ability to fabricate major components of the nuclear steam supply system (NSSS) in a factory environment and then transport them to the site. This can help limit the on-site preparation and also reduce the construction time. This is very important since the lengthy construction times are one of the key problems of the larger units. Moreover, the in-factory fabrication and completion of major parts of the nuclear steam supply system can also facilitate the implementation of higher quality standards (e.g., inspections of welds).
Construction time and financing
Size, construction efficiency, and passive safety systems (requiring less redundancy) can reduce a nuclear plant owner’s capital investment due to the lower plant capital cost. In-factory fabrication of major components of a nuclear steam supply system can significantly reduce the on-site preparation and construction time. In turn, this can lead to easier financing than that for larger plants.
Most economic benefits (especially lower capital cost) stated are valid for n-th unit produced. Large-scale production of SMRs and initial orders for tens of units is required to achieve these economic benefits.
One of the very important barriers is licensing of new reactor designs. For example, in regulating the design, siting, construction, and operation of new commercial nuclear power facilities, the NRC currently employs a combination of regulatory requirements, licensing, and oversight. Historically, the licensing process was developed for large commercial reactors, and the licensing process for new reactor designs is a lengthy and costly process.