IRSN, Institut de radioprotection et de sûreté nucléaire

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Information memo about Small Modular Reactors (SMR)

​Nuclear modular reactors of less than 300 MWe (or small modular reactors - SMRs) have sparked growing interest in the world for several years.

For their promoters, they constitute a means of producing energy that can meet various needs, such as cogeneration1  or non-electrical applications (industrial heat, production of fresh water, of hydrogen etc.). They are a suitable solution for districts that are isolated or have limited infrastructure. Their designers also show off improved performance in terms of safety, thanks to intrinsic and passive safety systems. Some designs offer an architecture allowing the installation of several modules independent of each other to achieve a larger overall power (of the range of 600 - 800 MWe).
To answer the question of economic profitability, the SMR designers put forth a simplification of the design and a shorter duration of the construction phase by means of modular construction, standardization with the benefit of series production. Therefore, the SMR designers ask for harmonizing the safety requirements in force in countries wishing to acquire such reactors. Some of them believe that the safety requirements should be adapted due to the intrinsic safety features of these designs.
IRSN considers, on the contrary, that there is no need to revise downwards the safety requirements for SMRs. The simplification and the inherent safety features should benefit safety and the demonstration thereof through compliance with these requirements.

Download the IRSN information memo of October 07, 2021 "Small​​​​ Modular​ Reac​tors" (PDF)​


Con​siderations on the performance and reliability of passive safety systems for nuclear reactors

Pressurized water reactors currently operating in France are equipped with active safety systems requiring a power source, such as an electrical power supply, and also include passive safety features (nuclear fission reaction control and shutdown rods, hydrogen recombiners, etc.).

Due to their lower power, Small Modular Reactors can use passive residual power evacuation systems to be evacuated in the event of an accident, which do not require energy input to operate. The aim is to bring the reactor to a safe shutdown state and to be able to keep it there without the need for human intervention for a long period of time.

​The evaluation of systems that could be implemented by designers raises certain difficulties related to the justification of their efficiency and reliability. In this document, IRSN presents the characteristics of passive safety systems and sets out the questions associated with the evaluation of new systems of this type as well as the lines of research to be developed to respond to them.

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