Achievable Transmutation Rates for Trus and Llfps in Myrrha

SCK•CEN wants to fulfil a prominent role in the ADS field and is currently establishing a R&D programme to finalise the design of an ADS prototype. Therefore, the ADONIS system, initially intended for dedicated radioisotope production, was revisited to give birth to the Myrrha system. The need for ADS related R&D as well as the extension of current competencies within SCK•CEN and related institutes led to the study of a prototype ADS which would focus primarily on ADS related research, i.e. on materials and fuel research, on the utilisation of liquid metals and associated aspects, on reactor physics, and subsequently on applications such as transmutation and safety research on sub-critical systems. In this respect, the Myrrha system should become a new major research infrastructure for SCK•CEN supporting and enabling the international R&D programmes. Currently, the study and preliminary conceptual design of the Myrrha system is being finalised and the basic engineering phase has started. This study will also define the final choice of the characteristics of the facility depending on the selected fields of application to be achieved in this machine. The applications which are considered can be grouped in three blocks; i) continuation, and later on extension towards ADS, of the ongoing R&D programmes in the field of reactor materials, fuel and reactor physics research; ii) enhancement and triggering of new R&D activities such as waste transmutation, ADS technology, liquid metal embrittlement; iii) initiation of new competencies such as medical application (proton therapy, PET production,..), neutron beam applications. Myrrha will use an accelerator delivering a proton beam of (2 mA, 250 or 350 MeV). The spallation target is a liquid Pb-Bi volume circulating in a single closed loop. In its present design the spallation source is a windowless design. The sub-critical assembly is made of two consecutive zones of fuel rod lattices. Due to the main interest in research on the transmutation of TRUs, the first zone, consisting of MOX-type fuel rods with high Pu contents, forms a fast neutron spectrum region. In the present design, the fuel pins are inserted in a lead environment. This lead environment is either a solid block (cooled with a gas-circuit) or liquid lead, depending on the total power to be removed. The fast neutron zone is surrounded by a thermal neutron zone made of LWR UO2 fuel rods inserted in a water moderator. This thermal zone will allow to increase the multiplication factor to perform experiments related to LWR fuel research, radioisotope production and transmutation of LLFPs. In this paper we will report on the performances one can achieve in the present design of Myrrha concerning transmutation of TRUs such as Np, Pu, Am, and Cm in the fast neutron zone as well as of LLFPs such as I, Tc, Cs, and Zr in the thermal neutron zone.