Gas-cooled reactors take up a strong second role in France's R&D strategy on future nuclear energy systems as priority was given in 2005 to fast neutron reactors with multiple-recycle for their potential to optimally use uranium resource and minimize the long term burden of radioactive waste. Owing to the European past experience on sodium-cooled fast reactors (SFRs), this reactor type was logically selected as reference for a new generation fast neutron reactor intended to be tested as a prototype in the 2020s and be ready for industrial deployment around 2040. At the same time, the potential merits of a gas fast reactor (GFR) with ceramic clad fuel for a safe management of cooling accident are acknowledged for the potential of this reactor type to resolve critical issues of liquid fast reactors (safety, operability and reparability). A pre-feasibility report on a first concept of GFR was issued in 2007 that summed-up results of a 5-year international R&D effort on GFR fuel technology, reactor design and operating transient analyses. This report established a global confidence in the feasibility of this concept and its potential for attractive performances. Furthermore, it suggested directions of R&D to generate by 2012 an updated concept with improved performances and taking better benefit from GFR specific technologies. A second activity on gas-cooled reactors originates from the current interest of CEA's industrial partner AREVA in high or very high temperature reactors (V/HTR) for supplying hydrogen, synthetic hydrocarbon fuels and process heat for the industry. This activity currently encompasses R&D on V/HTR key technologies such as particle fuel fabrication, high temperature compact heat exchangers and coupling technologies to various power conversion systems. R&D on V/HTR and GFR are synergistic in various respects. The GFR can be viewed as a more sustainable version of the VHTR and synergies exist in research on heat resisting materials, helium system technology and power conversion systems. Both reactors require active research in materials and spur developments of new metallic alloys and ceramics applicable to other advanced nuclear systems.

Les progres accomplis recemment dans le domaine des materiaux et des composants a haute temperature remettent sur le devant de la scene les reacteurs a caloporteur gaz qui ont deja connu un premier essor avec les reacteurs Magnox et UNGG. Dans leur version a neutrons lents, des realisations a l'echelle industrielle sont envisageables a moyen terme. Dans leur version a neutrons rapides, plus prospective, les reacteurs a caloporteur gaz offrent des perspectives supplementaires de valorisation energetique des ressources en uranium naturel, dans le cadre d'un cycle du combustible minimisant les dechets ultimes et le risque de proliferation. La presente monographie, premier ouvrage de la collection apres le hors-serie de presentation, decrit les recherches en cours sur ce type de reacteur, en montrant les enjeux, les resultats recents obtenus par le CEA et les obstacles qu'il reste a franchir.

The sodium fast reactors are the natural Generation IV candidate, thanks to their strong potential for incineration and/or breeding that allow drastic fissile materials economy and fission waste products recycling or transmutation. The question is now to make evolve the existing or past projects of reactors to systems fully compatible with Generation IV objectives, in particular with regard to the economy, durability and safety. This work must be achieved in an international frame which requires a sharing of the objectives and will allow, in the long term, the sharing of the activities. However, in order to ensure the overall coherence of the various development programs defined within the Gen-IV framework, it is necessary to define a new SFR development plan based on the experience gained in France (Phenix, Superphenix) and Europe, in the EFR project. The commonly agreed SFR system issues to be improved or further investigated are its capital cost, safety issues (sodium risks, core criticality accidents), and in-service inspection and maintenance technology. (authors)

Third generation reactors proposed to the market are mostly LWR, pressurized or boiling, with confirmed competitiveness. A special effort to increase the safety level is sensible and should be improved. At least, solutions are studied to better use plutonium. The development of a new generation of NPP’s offers opportunity to have another step towards more safety, for example in being fail-safe, and towards a minimization of ultimate waste produced. In this field, CEA dedicates its main effort to the development of a gas cooled reactor and constraint on safety, waste minimization are indicated. At least some examples of progression in the safety level of a plant are shown from an existing one to an hypothetical future reactor.