The MYRRHA-FASTEF cores design for critical and sub-critical operational modes (EU FP7 Central Design Team project)

On April 2009, a three-year-project was launched within the 7th Framework Programme (FP) of the European Commission: the Central Design Team (CDT) for a FAst Spectrum Transmutation Experimental Facility (FASTEF). The main goal was to achieve an advanced level of design for an irradiation facility, cooled by lead-bismuth, operating in both critical and sub-critical modes. In continuity with the research studies on fast nuclear systems carried out in the 5-6th FPs, the CDT had the further ambitious objective to define a preliminary design of the MYRRHA reactor, planned to be built at the SCK.CEN research centre in Mol (Belgium). In addition to being a multi-purpose irradiation facility, MYRRHA should be able to demonstrate the Acceleration Driven System concept at 100 MW power level and an efficient transmutation of minor actinides, as main contributors to high-level long-lived radioactive wastes. This paper describes the design of cores able to operate the MYRRHA-FASTEF plant in both critical and sub-critical modes. The design studies were performed by detailed neutronic analyses (with deterministic and Monte Carlo methods) and by accurate thermal-hydraulic evaluations (at the fuel assembly and pin sub-channel level), by taking also into account thermo-mechanical and safety constraints. Among the most significant core features, the fast flux level (Phi(>0.75 MeV) similar to 10(15) Cm-2 S-1), the high flexibility for irradiation purposes and the limited overall dimension (impacting on the cost of the plant) can be noticed. The transmutation of minor actinides, enhanced by the high fast flux, reaches values of about 32 kg(HM) TWh(-1) in both operational modes. (C) 2013 Elsevier B.V. All rights reserved.