IRSN, Institut de radioprotection et de sûreté nucléaire

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Generation IV nuclear energy systems: IRSN presents an overview of the "safety potential" of the systems studied in the context of the Generation IV International Forum


The « Generation IV International Forum » (GIF), created in 2000 by the United States Department of Energy (US/DOE), coordinates research and development work aimed at deploying Generation IV nuclear energy systems (reactors and the related fuel cycle facilities), by the second half of this century.

In this framework, the GIF has selected six systems among those proposed by the participating countries, including France:

  • Sodium-cooled Fast Reactors (SFR);
  • Very High Temperature Reactors, with thermal neutron spectrum (VHTR);
  • Gas-cooled Fast Reactors (GFR);
  • Lead-cooled Fast Reactors or Lead-Bismuth Eutectic (LBE) cooled Fast Reactors (LFR);
  • Molten Salt Reactors (MSR), with fast or thermal neutron spectrum;
  • SuperCritical Water Reactors (SCWR), with fast or thermal neutron spectrum.

IRSN carried out a review of these systems from the point of view of safety and radiation protection.

The difficulties of performing a “balanced” safety and radiation protection review of the nuclear systems selected by GIF should be underlined, as some concepts have already been partially tried and tested, while others are still in the early stages of development. Moreover, the safety of a nuclear facility depends both on the intrinsic characteristics of the facility in question and the design and operating provisions implemented. For that reason, it is impossible to make a comprehensive assessment of the different systems at this point in time and designs currently under consideration may not necessarily be those ultimately selected for Generation IV reactors and the related fuel cycle.

IRSN’s assessment thus seeks to measure the “safety potential” of the systems in question as far as can be determined on the basis of current knowledge.

Download IRSN report « Review of Generation IV Nuclear Energy Systems » (PDF, 4,45 Mo)


On the basis of its examination, IRSN considers the SFR system to be the only one of the various nuclear systems considered by GIF to have reached a degree of maturity compatible with the construction of a Generation IV reactor prototype during the first half of the 21st century; such a realization, however, requires the completion of studies and technological developments mostly already identified.

The main advantage of SFR technology in terms of safety is the use of low-pressure liquid coolant. The normal operating temperature of this coolant is significantly lower than its boiling point (margin of about 300°C), allowing a grace period of several hours during loss-of-cooling events. The advantage gained from the high boiling point of sodium, however, must be weighed against the fact that the structural integrity of the reactor cannot be guaranteed near this temperature.

The use of sodium also comes with a number of drawbacks due to its high reactivity with water and air. While it seems possible for SFR technology to guarantee a safety level at least equivalent to that targeted generation III pressurised-water reactors, IRSN is unable to determine whether it could significantly exceed this level. The nuclear system associated with the SFR has been the focus of considerable R&D, both in France and abroad, including the ASTRID  reactor project, which should enable safety improvements.

The VHTR benefits from the operating experience feedback obtained from High Temperature Reactors (HTR) and could bring about significant safety improvements compared with Generation III reactors, especially regarding core melt prevention. The feasibility of the system, however, has yet to be determined; it will chiefly depend on the development of fuels and materials capable of withstanding high temperatures, the currently considered operating temperature of around 1000°C being close to the transformation temperature of materials commonly used in the nuclear industry.

No operating experience feedback from the other four systems studied can be put to direct use. The technological difficulties involved rule out any industrial deployment of these systems within the time frame considered. Nevertheless, a distinction can be made between the LFR and GFR systems on the one hand, for which small reactors could be built during the first half of this century, and the MSR and SCWR systems on the other, where it seems hard to imagine any reactor being built before the end of the century.

At the present stage of development, IRSN does not notice evidence that leads to conclude that the systems under review are likely to offer a significantly improved level of safety compared with Generation III reactors, except perhaps for the VHTR, whose feasibility is however not acquired.

There is still much R&D to be done to develop the Generation IV nuclear reactors, as well ass for the fuel cycle and the associated waste management which depends on the system chosen. In any case, IRSN considers that the future generation of nuclear facilities would benefit from the development of “tolerant” concepts that are not highly sensitive to events liable to occur inside or outside the facility.

Lastly, for IRSN, regardless of economic competitiveness issues, it should be borne in mind that any decision to deploy a particular type of Generation IV reactor on an industrial scale will be based on its advantages not only in terms of the operation and safety of the reactors, but also in terms of the coherence and performance of the associated fuel cycle, including aspects related to safety, radiation protection, materials management and minimization of the quantities of radioactive waste produced.

Download IRSN report « Review of Generation IV Nuclear Energy Systems » (PDF, 4,45 Mo)

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