1 Copyright © 2014 by ASME Proceedings of the 2014 22nd International Conference on Nuclear Engineering ICONE22 July 7-11, 2014, Prague, Czech Republic ICONE22-31026 MOLTEN SALT FAST REACTOR BLANKET DESIGN AND PROLIFERATION RESISTANCE ASSESSMENT Valentyn Bykov Swiss Federal Institute of Technology in Zurich ETHZ, 8092 Zurich, Switzerland BykovV@student.ethz.ch Jiri Křepel Paul Scherrer Institut PSI, 5232 Villigen, Switzerland Jiri.Krepel@psi.ch Andreas Pautz Paul Scherrer Institut PSI, 5232 Villigen, Switzerland Andreas.Pautz@psi.ch ABSTRACT Molten Salt Reactor (MSR) designs are frequently accompanied by a blanket salt. This way the irradiation of the outer reactor wall will be strongly reduced. On the other hand, the barrier between the core and blanket will undergo higher irradiation and it will be necessary to replace it several times during the reactor lifetime. Furthermore, this blanket salt will also have a positive impact on neutron economy by improving the breeding performance. In this paper a blanket of a generic two fluid molten salt reactor utilizing fast thorium-uranium cycle was investigated. This was done by tracking the evolution of uranium, neptunium and plutonium isotopes with burnup, which was then influenced by removal of uranium from the blanket. A significant reduction in the production of minor actinides was observed. The uranium vector removed from the core was then investigated for proliferation resistance, using NUREC proliferation resistance metric and comparison with other weapon designs. The evaluation concluded that while the presence of U-232 increases radiological hazard associated with this uranium, thereby erecting a radiological barrier, it cannot be treated as “self-protecting” based on IAEA and NRC standards, requiring 1 Sv/h at 1m dose rate. Moreover ideas on how an interested party could reduce this radiological hazard were discussed. INTRODUCTION Molten Salt Reactors (MSR) is a class of nuclear reactors in which the fuel is dissolved in a molten salt, acting as a coolant. The fact that the fuel is liquid makes the MSR design a very unique one. This is reflected in certain advantages over solid fuel reactors, but also in a unique behavior during transients, which needs to be well understood in order for these reactors to be deployed [1-3]. Compared with other reactor designs, MSRs offer an excellent neutron economy, ability to burn transuranic elements and operated on a thorium-uranium cycle. Moreover its unique design offers inherent safety against certain types of accident. One cannot have a core melt in a molten core reactor. However, the molten salt can leak through molten structures, e.g. piping. The MSR design also raises several engineering challenges, which need to be resolved before the reactor can be deployed. These challenges mainly relate to the hostile environment inside the reactor and its effect on materials: namely the combination of irradiation damage and corrosion. One way to reduce irradiation damage is by reducing the neutron flux. This can be done by introducing a blanket salt, which will reduce neutron leakage. Furthermore, this blanket salt will also have a positive impact on neutron economy by improving the breeding performance [1]. In this way the irradiation of the outer reactor wall will be strongly reduced. On the other hand, the barrier between the core and blanket will undergo higher irradiation and it will be necessary to replace it several times during the reactor live time. This report will investigate the effect of the blanket salt on both neutron leakage and breeding performance. Different sizes of the blanket salt will be analyzed in order to determine the optimum size for the desired function. Another aspect analyzed in this report is proliferation resistance of the blanket. This is a concern frequently raised in connection with blankets, as they may be designed to breed very high purity fissile material. Specifically, in this report the