Small Modular Reactor – SMR

Small modular reactors (SMRs) are nuclear fission reactors which 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 which produce power output of less than or equal to 300 MWe. It must be noted, 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 the context of SMRs refers to its scalability and to the ability to fabricate major components of the nuclear steam supply system (NSSS) in a factory environment and then transported to the site. Its scalability means that some of 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, its scalability, modularity, robust design and enhanced safety features of the SMR offers great advantages over large commercial reactors. It must be noted, this reactor design is currently (2018) at the stage of development, however their technology is similar to proven naval reactors.

SMRs have potential in expanding countries for enhancing the energy supply security both and embarking countries, which have inadequate infrastructure or less established grid system (not suited for large commercial reactors). However, SMRs have 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.


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 taken into account during decision making.

Possible Advantages

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 very important safety feature in the SMR. Therefore there is less reliance on active safety systems and additional pumps, as well as AC power for accident mitigation. These passive safety systems are able to dissipate heat even after loss of offsite power. The safety system incorporates an on-site water inventory which operates on natural forces (e.g. natural circulation). In reactor engineering, natural circulation is very desired phenomenon, since it is capable to provide reactor core cooling without coolant pumps, so that no moving parts could break down.


As was written, the term “modular” in the context of SMRs refers to its scalability and to the ability to fabricate major components of the nuclear steam supply system (NSSS) in a factory environment and then transported 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 key problems of the larger units. Moreover, the in-factory fabrication and completation of major parts of the nuclear steam supply system can also facilitate 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 nuclear steam supply system can significantly reduce the on-site preparation and also reduce the construction time. This in turn can lead to easier financing compared to that for larger plants.

Possible Disadvantages

Large-scale Production

Most of the economic benefits (especially lower capital cost) stated are valid for n-th unit produced. In order to achieve these economic benefits, large-scale production of SMRs and initial orders for tens of units is required.


One of 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. The licensing process for new reactor designs is a lengthy and costly process.

Reactor Physics and Thermal Hydraulics:

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