Small Modular Nuclear Reactors (SMRs)

 Small Modular Nuclear Reactors (SMRs): Next Generation of Nuclear Technology?

A major challenge for engineers and scientists over the next decades is to develop and deploy power plants with sufficient capacity and flexibility to meet the growing demand for energy whilst simultaneously reducing emissions. Since clean and affordable energy is one of the united nations' sustainable development goals [1], nuclear energy is the most suited to this task as it is the most reliable clean energy source among other volatile sources like wind and solar energy [2]. But the higher construction and maintenance cost, limited baseload power production, and recent incidents like Fukushima nuclear plant meltdown prevented the deployment of new Large Reactors (LRs) in most countries and it led to the growing interest of academics, practitioners, and governments towards Small Modular Nuclear Reactors (SMRs).

SMRs are "newer generation [nuclear] reactors designed to generate electric power up to 300 MW, whose components and systems can be shop fabricated and then transported as modules to the sites for installation as demand arises" [3]. (Page 1). Currently, there are about 50 SMR designs at different stages of development [4] and some of these are claimed as near deployable. There are four SMRs in the advanced phase of construction [4] and two floating SMRs in operation (Akademik Lomonosov 1 and 2 (35 MW each) in Russia) [5]. SMR designs adopt both mature and proven technologies such as light water reactor (the technology used by the vast majority of Nuclear Power Plants in operation), less mature technologies such as sodium-cooled reactor, and "never commercially operated" technologies such as molten salt fueled (and cooled) advanced reactor [3].

SMRs provide many solutions to conventional Large Reactors. LR power plants are extremely complex and expensive buildings. The building and reactor both built on-site and that complexity Couse to a higher capital cost [7]. In SMRs, the reactor is built in a factory and placed in the building at the late stage of construction. Due to this modularity, standardized components can be used in mass-scale reactor manufacture factories and bulk ordering of these components will reduce the cost [6]. Safety and quality standards of manufacturing can also regulate with relative ease.

Due to their mobile nature and low maintenance, SMRs could be broadly used by smaller utilities, by smaller countries with financial or infrastructural constraints, in isolated regions, or for distributed power needs.

LRs rely on external power systems such as AC grid power, backup generators, and batteries to cool down their reactor core in case of a powerless which increase the points of failure. But in SMRs its passive cooling system designed to function without any automated or manual interference. They are placed in a water reservoir to use natural water circulation and in an emergency, specialized valves opened to release the steam to release from the reactor to the containment vessel. Then the condensed steam flows down and enters the reactor through another set of valves and this recirculation reduces core temperature [6]. Additionally, in a power failure, SMRs shut themselves down indefinitely. This is because the control rods are held up by electromagnets and in the event of complete power loss the electromagnets stop working completely releasing the control rods back into the core blocking the reaction instantly.[6] The current goes from 200-megawatt thermal to about 10 in second. Then passive cooling cools down the reactor to 0.4-megawatt thermal in 30 days and can remain in this stage indefinitely at this point the transition from water cooling to air cooling [6]

Conventional reactors require regular maintenance and refueling. Usually, LRs have to be shut down every 18 months for refueling in a process that usually takes a month out of energy production. SMRs solve this issue by having long refueling cycles. As an example, 5MW SMR from USN cooperation require no refueling in its 20-year operational lifetime and the Canadian 100MW ARC-100 SMR also has a similar 20-year refueling cycle.[8]
Despite its relative advantages, SMRs technology is still in the development phase and its navel approaches in the design and deployment pose challenges to the existing regulatory framework. According to International Atomic Energy Agency (IAEA), to demonstrate the safety of the design of a nuclear power plant of this kind, a comprehensive safety assessment of all plant states (normal operation, anticipated operational occurrences and accident conditions) is required. SMR designs and concepts of operation may challenge existing laws and regulations and may need to be modified or created to facilitate their licensing. [9]
In the current global situation where carbon emission should be reduced immediately, Small Modular Nuclear Reactor technology represents a promising answer to a sustainable energy portfolio with cost effective and scalable solutions. However, there is still a long process of R&D to gain technical maturity to serve its initial purpose. Nevertheless, this achievement really brings hope for a completely new generation of the most misunderstood technology ever created.

References:
United Nations. About the Sustainable Development Goals - United Nations
Sustainable Development. 2020. Available from: https://www.un.org/sustain.../sustainable-development-goals/
International Energy Agency. Global Energy & CO2 Status Report. 2019.
IAEA. Advances in Small Modular Reactor Technology Developments. 2018.
IAEA. Small modular reactors (SMR) | IAEA. 2020. Available from:
https://www.iaea.org/topics/small-modular-reactors
Mignacca, Benito, Giorgio Locatelli, and Tristano Sainati. "Deeds not words: Barriers and remedies for Small Modular nuclear Reactors." Energy 206 (2020): 118137.

Locatelli, Giorgio, Chris Bingham, and Mauro Mancini. "Small modular reactors: A comprehensive overview of their economics and strategic aspects." Progress in Nuclear Energy 73 (2014): 75-85.
Vegel, Benjamin, and Jason C. Quinn. "Economic evaluation of small modular nuclear reactors and the complications of regulatory fee structures." Energy Policy 104 (2017): 395-403.
“The ARC-100 Advanced Small Modular Reactor,” Carbon Free Energy Technology | ARC Clean Energy. [Online]. Available: https://www.arcenergy.co/technology.
M. Gaspar, “Technology Neutral: Safety and Licensing of SMRs,” IAEA, 17-Aug-2020. [Online]. Available: https://www.iaea.org/.../technology-neutral-safety-and...