An application of Cyclotrons for subcritical Molten Salt Reactors

Advantages of the subcritical burner-reactor application In order for die closed fuel cycle to be flexible it is necessary to use burner-reactors in nuclear power in the future. In our opinion, die best candidate for the burner-reactor is a subcritical molten-salt reactor fed by an external source of neutrons from a charged particle accelerator. There are the following reasons to consider subcritical reactors: o if die subcriticality is sufficiently great the reactivity accidents are completely impossible; o once die accelerator is disconnected, the reactor stops in (0.001-1) sec, i.e. the accelerator is an additional independent means of reactor control with practically no inertia. Search for a design with safe and at the same time considerable neutron multiplication which would allow die efficient use of electron accelerators or an isochronous cyclotron led us to considering a cascade molten-salt subcritical reactor (CMSR). This reactor is based on a well known principle of neutron multiplication in the coupled subcritical fast-thermal cores. In a chosen design a reactor with thermal capacity of 1250 MW consists of two cylindrical cores. The fuel salts 53NaF-41ZrF4-6XF4 and 69LiF-28BeF2-5XF4 circulate in cores AZ-I and AZ-2, respectively, as follows, the AZ-1 melt is supplied through the piping to the bottom area of the central core and dien flows upwards along a draught section 12 m in height and 30 cm in diameter where an external source channel is inserted and than arrives at the market part of an intermediate heat exchanger. The AZ-2 melt enters the top area of the core, flows downwards in the periphery of die core and then upwards along a drought section 12 m in height and 1.2 m in diameter to arrive at the intermediate heat exchanger. The photonuclear neutrons multiply in the inner core and pass, with a noticeable probability to the outer core (D=400 cm, H=400 cm) having a thermal neutron spectrum. The majority of fission (95%) occur in die outer core. The thermal neutrons penetrating from the outer core into the inner one are absorbed mainly by samarium. Thus the thermal neutron feedback between the cores is practically turned off which is a necessary condition for implementing the cascade design. If the partition wall between the cores is destroyed, the samarium will be distributed over the thermal zone, and, therefore, the CMSR will become more subcritical. This and some other features give CMSR properties of inherent safety. To determine a possibility for decreasing the intensity of the external neutron source in an MSR with Keff=0.98 die effect of die source insertion area on the size of the source were investigated at a given thermal capacity Wt = 1250 MW. The results obtained are listed in Table 1. The minimum intensity of the external source was obtained in the case when it is inserted in the central area of a 30 cm diameter core;Smin=1.14-10l7n/s. A CMSR reactor with Keff= 0.99 possesses essentially the same safety level as a subcritical single-core thermal MSR with Keff = 0.98. According to the accepted safety standards such a reactor is practically a nuclear fuel storage facility and requires no control and protection system