Gas Centrifuge Research Articles

Isotopically modified molybdenum for safe nuclear power

The possibility of applying isotopically modified molybdenum like the structural material of fuel elements for light-water and fast reactors with dispersed fuel containing granules of the metal U–Mo-alloy in Mo matrix, has been discussed. It has been shown that with isotope-modified molybdenum with the neutron capture cross-section close to natural zirconium, the improved safety of nuclear reactors, i.e., both thermal and fast-neutron reactors, due to the improvement of heat-transfer emission in fuel elements has been achieved. Assessments demonstrated that molybdenum with economic practical cost may be obtained on the existing cascades of gas centrifuges developed for the separation of nonuranium isotopes.

The computer simulation of 3d gas dynamics in a gas centrifuge

We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there.

Homotopic method applied to solving the flow field in a gas centrifuge

To investigate the flow field in a hyper-speed gas centrifuge, a hybrid difference scheme is used to discretize the axisymmetric Navier-Stokes equation. Source terms are included to simulate the injection and extraction of gas, also the mechanical drive of the scoops. The nonlinearity is obvious as the drive is strong. A Newton iteration used to solve the equation system becomes sensitive to the initial guess of the solution, which makes it difficult to converge. A homotopic method with self-adaptive steps is adopted to cope with this problem and to accelerate the iteration process. Numerical experiments simulating different strengths of scoop drive prove the effectiveness of the algorithm.

Distribution of the Transit Flow in the Rotor of a Gas Centrifuge

The present work is devoted to computation of the distribution of the transit flow in the rotor of a separation gas centrifuge. The existing transit-flow models have been considered, the equation to find the transit flow has been obtained, and the basic properties of the transit flow have been analyzed. The general equation for the transit-flow distribution has been obtained, and the transit-flow distribution for a simplified scheme of feed supply, extraction, and waste has been calculated.

Waves in a gas centrifuge

Impact of the pulsed braking force on the axial gas circulation and gas content in centrifuges for uranium isotope separation was investigated by the method of numerical simulation. Pulsed brake of the rotating gas by the momentum source results into generation of the waves which propagate along the rotor of the centrifuge. The waves almost doubles the axial circulation flux in the working camera in compare with the case of the steady state breaking force with the same average power in the model under the consideration. Flux through the hole in the bottom baffle on 15% exceeds the flux in the stationary case for the same pressure and temperature in the model. We argue that the waves reduce the pressure in the GC on the same 15%.

3D numerical study of a feed jet in a rotating flow-field

A contribution of a feed drive in the total counter-current flow in a gas centrifuge for isotope separation is an important problem in optimization of its separation performance. A 3D model is used to simulate flow structures of a feed jet in a rotating flow-field. By using a CFD code, the details of a feed jet are obtained under the axial feed jet boundary condition. It is demonstrated that because of the vacuum regime in the region near the axis of rotation, the results of numerical simulation of a CFD code bring errors. The 3D DSMC simulation is a feasible method to overcome this problem in the future.

Dependence of optimal separative power of the “high-speed” Iguasu centrifuge on pressure of working gas

The results of optimization calculations of the separative power of the ’’high-speed” Iguasu gas centrifuge are presented. Iguasu gas centrifuge has the rotational speed of 1000 m/s, the rotor length of 1 m. The dependence of the optimal separative power on the pressure of the working gas on the rotor wall was obtained using the numerical simulations. It is shown, that maximum of the optimal separative power corresponds to the pressure of 1100 mmHg. Maximum value of separative power is 31.9 SWU.

Determination of the optimal mesh parameters for Iguassu centrifuge flow and separation calculations

We present the method and the results of the determination for optimal computational mesh parameters for axisymmetric modeling of flow and separation in the Iguasu gas centrifuge. The aim of this work was to determine the mesh parameters which provide relatively low computational cost whithout loss of accuracy. We use direct search optimization algorithm to calculate optimal mesh parameters. Obtained parameters were tested by the calculation of the optimal working regime of the Iguasu GC. Separative power calculated using the optimal mesh parameters differs less than 0.5% from the result obtained on the detailed mesh. Presented method can be used to determine optimal mesh parameters of the Iguasu GC with different rotor speeds.

Magnetron sputtering of copper on thermosensitive polymer materials of the gas centrifuge rotors

Magnetron sputtering is the well-known and widely-used deposition technique for coating versatile high-quality and well-adhered films. However, the technology has some limitations, caused by high temperatures on the coating surface. The paper is devoted to the experimental development of a process of magnetron sputtering of copper on a surface coated with a thermosensitive polymer made of carbon fiber with epoxide binder. This process is applied for balancing a rotor of a gas centrifuge for isotope separation. The optimum operating parameters of the process are found and discussed. They were in quantitative agreement with data obtained by means of non-stationary modeling based on a global description of plasma in the typical geometry of the magnetron discharges obtained in independent research. The structure of the resulting layer is investigated.

Two optimal working regimes of the ”long” Iguasu gas centrifuge

We argue on the basis of the results of optimization calculations that the dependence of the optimal separative power of the Iguasu gas centrifuge with 2 m rotor has two local maxima,corresponding pressures of pmax1 = 35 mmHg and pmax2 = 350 mmHg. The optimal separative power values in these maxima differ by the value of 0.6%. Low pressure maximum is caused by the thermal drive, whereas high pressure maximum is caused by both thermal and mechanical drives. High pressure maximum is located on wide ’’plateau” from p1 = 200 mmHg to p2 = 500 mmHg, where the optimal separative power changes in the range of 0.7%. In this way, Iguasu gas centrifuge has two optimal working regimes with different sets of working parameters and close slightly different values of the separative power. Calculations show that high pressure regime is less sensitive to the parameters change than low pressure one.

Evaluating the effectiveness of dilution of the recovered uranium with depleted uranium and low-enriched uranium to obtain fuel for VVER reactors

The possibility of the recovered uranium enrichment in a cascade of gas centrifuges with three feed flows (depleted uranium, low-enriched uranium, recovered uranium) with simultaneous dilution of U-232,234,236 isotopes was shown. A series of numerical experiments were performed for different content of U-235 in low-enriched uranium. It has been demonstrated that the selected combination of diluents can simultaneously reduce the cost of separative work and the consumption of natural uranium, not only with respect to the previously used multi-flow cascade schemes, but also in comparison to the standard cascade for uranium enrichment.

Mathematical Modeling of Non-Stationary Hydraulic Process Occurring in the Gas Centrifuge Cascade During the Separation of Multicomponent Isotope Mixtures

This article presents results of development of the mathematical model of nonstationary separation processes occurring in gas centrifuge cascades for separation of multicomponent isotope mixtures. This model was used for the calculation parameters of gas centrifuge cascade for separation of germanium isotopes. Comparison of obtained values with results of other authors revealed that developed mathematical model is adequate to describe nonstationary separation processes in gas centrifuge cascades for separation of multicomponent isotope mixtures.

MATHEMATICAL MODEL OF NON-STATIONARY HYDRAULIC PROCESSES IN GAS CENTRIFUGE CASCADE FOR SEPARATION OF MULTICOMPONENT ISOTOPE MIXTURES

It is known that the optimal modes of gas centrifuge (GC) cascades are violated occurring the non-stationary hydraulic processes for a separation of multicomponent isotope mixtures. The perturbation arise and lead to violations of operating specifications and intolerable overloads equipment. The non-stationary hydraulic processes affect the cascade efficiency and the quality of the product. The GC cascades for the separation of multicomponent isotope mixtures have insignificant gas content, and, as a consequence, low inertia. It leads to increased influence of non-stationary processes on the cascade efficiency. In this regard, an important urgent task is the comprehensive investigation and modeling of these processes. We solved this problem by creating mathematical model and software for it. The separation stage of the GC cascade is presented in the form of four dedicated object (a feed manifold, GC, a heavy fraction manifold and a light fraction manifold). The calculation of non-stationary hydraulic amounts to replacing the first order differential equations by difference equations of the implicit Euler scheme [1] and the decision obtained by non-linear algebraic equations. The calculation is iteratively performed; the pressures and flow are determined in all objects at each time step, satisfying the equation of material balance in the cascade. These values must satisfy the balance of substances in the GC cascade. The developed mathematical model was tested for isotope separation of Si, Xe, Ni, W. The deviation of the calculated and actual values was 7.5%. As a result, this mathematical model is universal for calculation of hydraulic parameters of GC cascades for separation of multicomponent isotope mixtures by using different working substances.

Separative Power of an Optimised Concurrent Gas Centrifuge

Abstract The problem of separation of isotopes in a concurrent gas centrifuge is solved analytically for an arbitrary binary mixture of isotopes. The separative power of the optimised concurrent gas centrifuges for the uranium isotopes equals to δU = 12.7 ( V /700 m/s) 2 (300 K/ T )( L /1 m) kg·SWU/yr, where L and V are the length and linear velocity of the rotor of the gas centrifuge and T is the temperature. This equation agrees well with the empirically determined separative power of optimised counter-current gas centrifuges.

Experimental investigation of effects of the feed flow rate and “tail scoop-wall” clearance on the performance of a gas centrifuge by feeding a Freon mixture

ABSTRACTExperimental study of the performance of a gas centrifuge can be appreciably simplified if instead of isotopic mixtures, a binary mixture of gases with large molecular weight difference is used. The current study undertook this approach by injecting a 53%–47% (w/w) mixture of “Freon12-Freon22” into a gas centrifuge. The two parameters, whose investigation was the objective of the current study were: the feed flow rate (F), and the clearance between tail scoop and the rotor wall (d). The results demonstrated that changing the scoop-wall clearance has the most significant effect on the cut (θ), so that by fixing “d”, “θ” becomes nearly invariant. The head separation factor (α) exhibited the same dependency, but it was more influenced by the “F” than the “d”. Apparently the following regression exists between the inspected parameters:Decreasing “d” → Decreasing “θ” → Increasing “α”.Variations of the tail separation factor (β) with “F” or “d” was quite slight, even though similar to “α”, it was lowered with increasing of the “F”. The separation capacity (δU) as the most significant parameter of a centrifuge was optimised at the highest value of “F = 40.5 g/h”, and lowest value of “d = 3 mm”. The study achieved a separation capacity and an overall separation factor equal to 195.53 kg Freon/y and 16.87, respectively. These values are several times larger than those of the isotopic mixtures, demonstrating that application of Freons is a useful mean for magnifying the features of a gas centrifuge.

Influence of 236U on the Efficacy of Recycling Regenerated Uranium in VVER Fuel

This scientifi c and technical communication examines the physical mechanisms of the change in the isotopic composition of regenerated uranium recycled in VVER-1000 and -1200 fuels. Modeling of the Multiple Recycling of Regenerated Uranium. An approach based on matched modeling of the neutron-physical processes occurring during the irradiation of fuel in a reactor and molecular-selective mass transfer in separative cascades of gas centrifuges for the enrichment of uranium is used to investigate the mechanisms. The approach is very similar to that used in [1, 2]. Aside from the asymptotic case, where multiple recycling of regenerated uranium with dilution of natural uranium is accomplished without restrictions on the U content in low-enriched uranium, scenarios in the presence of such restrictions are analyzed. The following recycling sequence is considered [3]. The fuel in the initial load with prescribed enrichment of U fabricated from natural uranium is irradiated in the reactor core, allowed to decay for 10 yr, and reprocessed. Natural uranium is the second feed stream of the cascade, making it possible to dilute the regenerated uranium and lower the content of U in the product. The fuel obtained in this manner is once again irradiated, after which it is allowed to decay and then reprocessed. Next, the cycle is repeated. In all, fi ve successive recycles of the regenerated uranium are considered. Multiple recycling of regenerated uranium by burnup to 48 MW·days/kg with different restrictions on the U content in low-enrichment uranium was analyzed fi rst. Three cases were considered. The U concentration did not exceed 2·10 wt.% in the fi rst case and 5·10 wt.% in the second; there were no restrictions on the U concentration in the third. The effect of U was compensated by additional enrichment with U and reactivity compensation factor 0.29 [3, 4]. The restriction on the U concentration in low-enrichment uranium at the level 0.1% was examined separately; compensation of the parasitic absorption of neutrons by this isotope is not required below this level. The burnup considered in the present work corresponds to the maximum unfavorable situation from the standpoint of the content of U and U in the regenerated uranium. For example, burnup 48 MW·days/kg with 4% enrichment is reached only in individual fuel assemblies. The average burnup with such enrichment equals 43 MW·days/kg. A model of a quasi-ideal cascade, widely used in the theory of separation of multicomponent isotopic mixtures, is used for numerical modeling of the enrichment of regenerated uranium in a cascade with two feed streams (natural uranium and regenerated uranium) [5]. This model is used as a replacement for an ideal cascade, often used in the evaluation of the parameters of cascades for enrichment of natural uranium, because regenerated uranium, in contrast to natural uranium, cannot be regarded as a binary mixture, since it contains, aside from U, a fourth component – U, U, U, or U [6]. The neutron physical processes were calculated by the Monte Carlo method using the MCNP5 code (USA).

A Game Theoretic Approach to Nuclear Safeguards Selection and Optimization

ABSTRACTThis article presents a novel application of an inspection game to find optimally efficient nuclear safeguard strategies. It describes a methodology that allocates resources at and across nuclear fuel cycle facilities for a cost-constrained inspectorate seeking to detect a state-facilitated diversion or misuse. The methodology couples a simultaneous-play game theoretic solver with a probabilistic model for simulating state violation scenarios at a gas centrifuge enrichment plant. The simulation model features a suite of defender options based on current International Atomic Energy Agency practices and an analogous menu of attacker proliferation pathway options. The simulation informs the game theoretic solver by calculating the detection probability for a given inspector-proliferator strategy pair. To generate a scenario payoff, it weights the detection probability by the quantity and quality of material obtained. Using a modified fictitious play algorithm, the game iteratively calls the simulation model until Nash equilibrium is reached and outputs the optimal inspection and proliferation strategies. The value the attacker places on material quantity and quality is varied to generate results representative of states with different capabilities and goals. Sample model results are shown to illustrate the sensitivity of defender and attacker strategy to attacker characteristics.

Mathematical Modeling of Nonstationary Separation Processes in Gas Centrifuge Cascade for Separation of Multicomponent Isotope Mixtures

Mathematical Modeling of Nonstationary Separation Processes in Gas Centrifuge Cascade for Separation of Multicomponent Isotope Mixtures

Rhie–Chow interpolation in strong centrifugal fields

Rhie–Chow interpolation formulas are derived from the Navier–Stokes and continuity equations. These formulas are generalized to gas dynamics in strong centrifugal fields (as high as 106 g) occurring in gas centrifuges.

Impact of the pulsed braking force on the axial circulation in a gas centrifuge

Impact of the pulsed braking force on the axial gas circulation in centrifuges for a uranium isotope separation was investigated by the method of numerical simulation. Two camera model has been explored. The pulsed braking of the rotating gas results into generation of waves which propagate along all length of the rotor of the centrifuge. The wavelength appears in accordance with predictions of our analytic theory. Pulsations almost doubles the axial circulation flux in the working camera in comparison with the case of the steady state breaking force with the same average power.