Final Report Summary - GDT-BURNER (A plasma neutron source based on the gas dynamic trap for incineration of radioactive wastes)
The issue of the transmutation of long-lived radioactive nuclear waste including plutonium and minor actinides (MA) represents a highly important problem of nuclear technology and is presently studied worldwide. Sub-critical systems seem to be a promising option for efficiently burning plutonium and minor actinides provided a sufficiently high-intense neutron source is available. Recently, the idea of coupling a sub-critical system and a plasma fusion device generating 14 MeV neutrons for the incineration and transmutation of long-lived isotopes of nuclear waste has attracted increasing interest. Reported project was aimed at R&D of the fusion neutron source for the transmutation of long-lived radioactive waste in spent nuclear fuel. The projected plasma type neutron source is based on the Gas Dynamic Trap (GDT) which is a special magnetic mirror system for the plasma confinement. The plasma physics calculations and optimisation of the neutron source's parameters have been performed with the Monte-Carlo method using the Integrated Transport Code System (ITCS). ITCS was developed for GDT simulations and includes different modules for plasma, particles transport and neutron production modeling. As a result, a new improved version of the fusion neutron source is proposed and numerically simulated. The proposed source is an axially symmetric mirror machine of the GDT type, 16 m long, and having a mirror ratio of 15. The plasma confined in the GDT includes two ion components with very different energies. One of the components is the background deuterium plasma with an isotropic Maxwellian distribution. The self-consistent electron and ion temperatures of this component extend up to 2 keV. This component is characterised by a gas-dynamic confinement regime because the mean free path of the ion scattering into the loss-cone is smaller than the mirror-to-mirror distance. So-called "fast" ions with energies of several tens of keV represent the second plasma component. It is built up by 65 keV neutral beams of deuterium and tritium injected into the target plasma under 30 degree to the axis of the device. This component is confined due to the conservation of magnetic moment and energy of the ions. The fast deuterons and tritons generate neutrons via fusion reactions. The parameters of background plasma and injected atoms are in such a relation that the characteristic slowing down time of the fast ions appears to be much smaller than the characteristic time for their scattering. Therefore, the fast ions retain a small angular spread close to that of the injected neutral beams while oscillating between the turning points near the end magnetic mirrors. Under these conditions the longitudinal profile of the fast ion density and the resulting fusion neutron flux are strongly peaked in the regions of the particle's reflection near the magnetic mirrors (n-zones), and the absolute values of the neutron flux in these regions is much greater than in the rest of the plasma chamber. The oblique injection of neutral beams thus enables to spatially separate the regions of the beam trapping and the neutron generation. The proposed neutron source has two n-zones of 2 m length with a neutron power of 1. 6 MW/m and a neutron production rate up to 1E18 n/s each. The machine requires a power input estimated as 120 MWel. This GDT neutron source can be used for application to a fusion driven system (FDS) for the burning of MA in spent nuclear fuel. One GDT-driver can be used for two sub-critical burners placed around the neutron emission zones. The considered sub-critical burner configuration was based on the reactor design of the European Facility for Industrial Transmutation (EFIT). As a result, the hybrid system with the two MA burners driven by one GDT neutron source can produce about 1 GW of fission power (~ 500 MWth at each side). Such system can incinerate in a year about 150 kg MA that corresponds to waste production by 5 LWRs.