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A plasma neutron source based on the gas dynamic trap for incineration of radioactive wastes

Final Report Summary - GDT-BURNER (A plasma neutron source based on the gas dynamic trap for incineration of radioactive wastes)

Increasing accumulation of the spent nuclear fuel from fission reactors is a problem which can be one of the main reasons to cancel the production of nuclear power, that already takes place in some developed countries. Because of exclusive importance of this problem, the optimum ways of liquidation of radioactive nuclear waste, including plutonium, minor actinides and long-lived fission products are presently studied worldwide in large-scale. Stations on processing and burning of long-living radioactive wastes on the basis of an offered neutron source can solve this problem completely. The potential consumers of such stations can be the international and national organisations on use of an atomic energy (IAEA, Euratom, Rusatom, etc.).

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 research and development (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.

In the first (incoming) phase of the project the plasma physics calculations and optimisation of the neutron source's parameters have been performed. As a result, a new improved version of the fusion neutron source is proposed and numerically simulated. The neutron source is suggested to be built as a plasma machine of gas dynamic trap (GDT) type. The GDT device in the Budker Institute (BINP), Novosibirsk, Russia is unique device of similar type and the second (return) phase was aimed to the reintegration of Dr A. Anikeev to the GDT research team as a leader of GDT-burner program. At project period, the GDT device in Budker Institute was upgraded. The GDT-U device is equipped by the new neutral beam injection system, which can generate 25 keV energy atom beams with total injection power up to 8 MW and duration of 5 ms. In a frame of the given project the modernisation of magnetic system was also completed. The magnetic field in mid-plane of the GDT-U devise was increased from 0.24 to 0.32 Tesla.

At this stage of investigations toward a powerful fusion neutron source, now a significant enhancement of plasma parameters is required and the findings hitherto collected have to be confirmed for the new plasma states. Also, the new parameter ranges raise new questions on plasma stability and equilibrium, which have to be answered. The main results of the return phase are:

- The electron temperature was increased up to the range of 200 - 250 eV. Such values of the electron temperature already allows one to build a neutron source, which will be capable of generating a moderate DT-fusion neutron flux density of about 0.3 MW/m2.
- The second important result is the demonstration of stable confinement of the two-component plasma with an electron temperature of 200 - 250 eV and related plasma pressure 'beta approximately 0.5 in special regimes, in which the density of fast ions averaged over entire length of the device was higher than the warm ion density. For this case, theories predict the possible appearance of strong ambipolar fields, which can cause a positive modification of the ion confinement mechanisms.

For observation of plasma property in GDT-U device, the wide set of plasma diagnostic and methods was used. The high-parameter experiments at the upgraded GDT device were accompanied by calculations using numerical codes, which have been developed in co-operation during the main phase of the project. The codes were adjusted to the new plasma conditions and then appropriately applied for calculating the new GDT-U experiments. The good agreement of calculation and measurement results enables to verify theoretical models included to the numerical codes and used for the proposed neutron source simulation and optimisation. The main output of the reported project is a physical demonstration of possibility of a GDT-based plasma-type neutron source with the moderate neutron emission. The next step of the GDT-burner's R&D is a new experimental device with powerful neutral beams and equivalent magnetic field up to 1 Tesla for full-scale experimental demonstration of the GDT-based neutron source properties.