SUMMARY AND R&D NEEDS

Corrosion mitigation strategies such as coatings and advanced materials are under development and qualification in liquid lead to support the operation of ALFRED LFR reactor in the later stages, where the primary cycle temperatures will be high enough to hinder the use of bare steels due to corrosion issues.

For fuel cladding structures, Al2O3 coating by PLD is the reference choice thanks to the excellent corrosion resistance in static liquid lead, the metal-like mechanical properties and the good performance under heavy ions irradiation. Long-term qualification in lead flowing conditions will be performed in the frame of GEMMA project to further validate this mitigation solution for fuel cladding structures, as well as mechanical tests in liquid lead will be performed.

Similarly, also Al2O3 layer from Detonation Gun, potentially considered as protective coating for reactor vessel, will be qualified from the point of view of the long-term corrosion in lead.

FeCrAl aluminizing such as pack cementation is considered for the protection of components with complex geometry. Although good results were obtained in recent years on aluminized steel substrates produced with small-scale pack cementation process, the need to coat large and complex components such as HXs or DHR requires the investigation of solution from industrial methods. About that, the qualification of industrial pack cementation process will be performed in liquid lead during GEMMA project.

AlTiN coating is considered for the protection of primary pump impellers for the high wear/erosion resistance, and it is industrially available. Preliminary exposure tests in liquid lead showed no evidence of corrosion but testing and qualification on prototype impeller component should be performed to assess finally the suitability for the protection of primary pumps.

Finally, short-term exposure tests of AFA steels showed that these materials are promising for their high corrosion resistance in liquid lead. Long-term corrosion tests will be performed in the future to fully qualify these materials and to investigate the need for optimizing the composition, which has to respect the requirements of corrosion resistance and preservation of the austenite structure.

ACKNOWLEDGEMENT

The results here described were obtained in the frame of several founded projects. The authors are grateful to the Italian Framework Program between ENEA and the Ministry of Economic Development (AdP MiSE-ENEA, B.3.1-LP2), the European project MATISSE (EURATOM FP7, n°604862) and the EUROFUSION Breeding Blanket project (n°633053) for the financial support.

The authors wish to thank also Dr Y. Yamamoto and Dr M. Brady from Oak Ridge National Laboratory (ORNL, USA) for providing AFA materials for corrosion tests in liquid lead.

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SOME NEW R&D FOCUS IN STRUCTURE MATERIALS LICENSING

Development and justification of service properties for materials used in reactor design and specific design solutions are inextricably connected. Special steels with increased corrosion resistance in the lead-bismuth coolant have been created and industrially mastered in Russia. A distinctive feature of these steels is the increased content of silicon as an alloying element that contributes to the stabilization of protective oxide films, limiting their diffusion permeability. Implementation of the fast neutron reactor SVBR-100 with lead-bismuth coolant required an extended study of the characteristics of radiation and corrosion resistance of the materials used. In the frame of R & D on materials substantiation, samples of reactor materials were irradiated to damage doses up to 25 dpa. As a result of performed researches the limits of the damage dose, beyond which the materials become unacceptably embrittled were determined. The basic mechanisms of radiation embrittlement and their regularities are established. Necessary measures were implemented to ensure the radiation resistance of materials for the entire design life (400 thousand hours). The second important result was the successful completion of corrosion resistance studies for the fuel rod cladding materials for a full lifetime (50 thousand hours).

At the same time, an important conclusion of the R&D program on substantiation of materials and works on project licensing was made. New focus formed on the need to expand the scope of necessary research to the field of extreme states of materials. These works are necessary to justify the project in area of severe accidents associated with beyond design basis core damage accidents.

1. INTRODUCTION

The development of the SVBR-100 reactor is based on the following basic principles:

— the project uses lead-bismuth coolant and mastered technology of dissolved oxygen control in the coolant to ensure corrosion resistance of materials;

— this is generation IV technology that can demonstrate, among other, how the inherent safety characteristic of fast neutron heavy liquid metal cooled (HLMC) reactors can be converted into cost savings;

— this technology is based on industrially available materials and technologies that have clear limits, including temperature limits, thus, design elements, materials, technological schemes, parameters and modes of operation have been optimized to exclude redundant systems and equipment, the volume of construction and finally – capital costs for plant construction.

At the initial stage of the project development the main structural materials were selected:

— EP-823 steel of ferritic-martensitic class;

— EP-302 steel of austenitic class;

— 08Х18Н10Т steel of austenitic class.

These materials meet the necessary requirements in terms of their characteristics, have been mastered by industry and tested in real operating conditions. Significant experience in BN reactors and the amount of experimental data on the characteristics of austenitic and ferritic-martensitic steels, including data on the effect of irradiation, are fully applicable to the SVBR project. Corrosion resistance and the possibility of using steels of these classes under certain temperature restrictions confirmed by both Russian and foreign studies [1,2,3].

At the same time, the existing practical experience and the volume of experimental studies performed (at the beginning of the SVBR project development) did not fully cover the new requirements for equipment lifetime and damaging factors typical for a fast neutron reactor [4].

The key issues that required confirmation at the initial stage of the project were:

— long-term corrosion resistance of fuel rod cladding materials;

— radiation resistance of reactor materials exposed to increased radiation damages.

These issues were solved at the first stage of the materials research program. The main results are presented below.

2. MAIN RESULTS OF MATERIALS CORROSION RESISTANCE JUSTIFICATION FOR SVBR -100