Design and first operation of the MACARON irradiation experiment of Sodium Fast reactor absorber pins in the BOR-60 reactor

Abstract The development of the next generation of Sodium-cooled Fast Reactors (SFRs) needs to integrate innovative options regarding the core design in order to comply with the objectives of the 4th generation reactors in terms of safety, cost and performance. In this framework, the aim to design fast core with economy improvements leads to limit the number of control and shutdown systems and to extend their lifetime. These objectives require choosing absorber material with maximal efficiency in terms of neutronic absorption. The French concept of absorber pin is based on the use of boron carbide (B4C) pellets with 10B various enrichments and the absorber element consists of a vented non-leaktight pin with a permanent sodium bond between the pellet column and the stainless steel clad. In order to test an innovative concept of absorber pin and with the aim to improve in one hand, the in pile behavior understanding and in the other hand, the absorber rod modelling codes, an experimental program named MACARON is undergone. This program consists in an irradiation test in the BOR-60 reactor following by a complete NDE and PIE program. Two short absorber pins are irradiated currently. This program is performed by both CEA and RIAR teams. A brief description of the experiment is first provided, in terms of objectives. The main characteristics of absorber pin with the main design criteria are detailed. The manufacturing steps and the characterization of the experimental absorber pins are given with as manufactured results. The design studies of the Irradiation Rig and the neutronic and thermal hydraulic calculations are described in details. The irradiation test has begun in September 2018 and the first experimental results are provided. The huge program of Non-Destructive and Destructive Examinations is detailed with experimental objectives and methods that will be used.