A. A. Samokhin

Study of charged particle motion in fields of different configurations for developing the concept of plasma separation of spent nuclear fuel

The concept of plasma separation of spent nuclear fuel in a plane perpendicular to the magnetic field in an electric potential of special configuration is developed. A specific feature of the proposed approach consists in using an accelerating potential for reducing energy and angular spread of plasma ions at the entrance to the separator chamber and a potential well for the spatial separation of ions with different masses. The trajectories of ions of the substance imitating spent nuclear fuel are calculated. The calculations are performed for azimuthal and axial magnetic fields and model electric field configurations corresponding to different geometries of the separator chamber. It is shown that, using magnetic fields with a characteristic strength of 1 kG and electric potentials of up to 1 kV inside a region with a linear size less than 100 cm, it is possible to separate ions of spent nuclear fuel with energies from 0.2 to 3 eV. The calculations were performed for a collisionless mode in the single-particle approximation. Possible variants of the experimental facility for plasma separation of spent nuclear fuel are proposed.

Explosive boiling in water exposed to q-switched erbium laser pulses

Pressure signals generated in water under the action of erbium laser pulses (100–200 ns, 2.94 μm) are investigated with lithium niobate piezoelectric transducer. For the first time multiply short (subnanosecond) pressure pulses standing against smooth pressure background are observed when the laser intensity exceeds explosive boiling threshold.

Photoacoustic and evaporation pressure signals in water irradiated with erbium laser pulses

Pressure signals in water exposed to erbium laser pulses with a duration of 200 ns, a wavelength of 2.94 µm, and an intensity modulated with a period of ∼ 5 ns due to mode beats were studied. It was found that the amplitude of the high-frequency component of the pressure signal, caused by this modulation, reproduces the behavior of the smooth component of the laser pulse shape at low irradiation intensities. As the intensity increases, behavior of the high-frequency signal amplitude is more complicated, showing significant decrease at certain instants of laser pulse exposures. Such behavior can be caused by the simultaneous effect of photoacoustic and evaporation mechanisms of pressure generation in irradiated liquid.

Photoacoustic effect upon material melting and evaporation by laser pulses

Photoacoustic signals in laser-irradiated samples were mathematically modeled for the cases when melting and evaporation occur. In particular, it was shown that rapid melting processes induced by nanosecond laser pulses result in a rather narrow pressure peak or dip in photoacoustic pressure signals due to density changes in the moving melting front. Amplitudes of these peaks or dips depend on the melting front velocity, as well as on the magnitude of density change. Experimental detection of this effect using a piezoelectric transducer requires a uniform laser intensity distribution over the irradiation spot.

Possibility of separating spent nuclear fuel components by a plasma method in azimuthal magnetic and radial electric fields

We consider the method of plasma separation of spent nuclear fuel in a system with an azimuthal magnetic field and the electric potential produced by electrodes located in a magnetized plasma. The results of calculation of trajectories of ions simulating uranium and the first peak of its fission products in the oneparticle approximation are described. The effect of the initial position and the initial velocity of ions on their trajectories is analyzed. The conditions ensuring the spatial separation of ions in the groups of masses admissible for practical realization are specified; it is shown that currents on the order of 100 kA through the central conductor and electrostatic potentials on the order of 1 kV are required for this purpose.

Designing of a lead ion model source for plasma separation of spent nuclear fuel

Plasma sources of model substances are required for solving problems associated with the development of a plasma separation method for spent nuclear fuel (SNF). Lead is chosen as the substance simulating the kinetics and dynamics of the heavy SNF component. We report on the results of analysis of the discharge in lead vapor with a concentration of 1012–1013 cm–3. Ionization is produced by an electron beam (with electron energy up to 500 eV) in the centimeter gap between planar electrodes. The discharge is simulated using the hydrodynamic and one-particle approximations. The current–voltage characteristics and efficiencies of single ionization depending on the vapor concentrations and thermoelectron current are obtained. The experimentally determined ion currents on the order of 100 μA for an ionization efficiency on the order of 0.1% are in conformity with the result of simulation.

Transmittance jump in a thin aluminium layer during laser ablation

A jump in the transmittance (from ~0.1% to ~50% for ~1 ns) of an optical gate on a Mylar film (a thin aluminium layer on a Lavsan substrate) irradiated by nanosecond (10-7 – 10-8 s) pulses of a neodymium laser with an intensity up to 0.1 GW cm-2 has been recorded. The mechanism of a fast (10-10 – 10-11 s) increase in the transmittance of the aluminium layer upon its overheating (without boiling) to the metal – insulator phase-transition temperature is discussed.

Effect of submillisecond radiation of the erbium laser on absorbing liquid

Pressure pulses occurring in water under the effect of submillisecond radiation of the Er3+:YAG laser on the free and covered liquid surface were measured. The behavior of pressure pulses is caused by the photoacoustic effect, explosive boiling of the superheated liquid surface layer, and cavitation processes developing after laser exposure.

Analysis of explosive boiling of a liquid film on an impulsively heated substrate

Explosive boiling of a thin liquid film on a substrate heated by nanosecond laser pulse, which results in film peeling from a substrate, is considered. It was shown that, to explain the experimental data [1] on the maximum film peeling velocity, the features of evaporation kinetics in the appearing cavity and the shaking effect associated with the nonlinear thermal expansion of the film immediately before its detachment from the substrate should be taken into account.

Heavy component of spent nuclear fuel: Efficiency of model-substance ionization by electron-induced discharge

The method of plasma separation of spent nuclear fuel can be tested with a model substance which has to be transformed from the condensed to plasma state. For this purpose, electron-induced discharge in lead vapor injected into the interelectrode gap is simulated using the kinetic approach. The ionization efficiency, the electrostatic-potential distribution, and those of the ion and electron densities in the discharge gap are derived as functions of the discharge-current density and concentration of the vapor of the model substance. Given a discharge-current density of 3.5 A/cm2 and a lead-vapor concentration of 2 × 1012 cm–3, the simulated ionization efficiency proves to be nearly 60%. The discharge in lead vapor is also investigated experimentally.