Deuterium-tritium Fusion Reaction Research Articles

Electrical conductivity of Li 2TiO 3 ceramics

The microstructure of Li 2TiO 3 ceramics, proposed as blanket material in deuterium–tritium fusion reactors, plays an important role for this application; grain size and grain shape determine to a considerable degree the properties in question. Electrical properties may reflect certain characteristics of the microstructure to some extent. In this communication impedance spectroscopy is applied to analyse electrical charge transport in ceramics of monoclinic β-Li 2TiO 3, synthesized in different conditions. Li + ions are suggested to be the majority charge carriers. Typical activation energies for charge transport, deduced from the DC conductivity σ DC, are E A ∼ 0.6–0.9 eV and the bulk σ DC (573 K) ∼ 3 × 10 − 6 Ω − 1 cm − 1 . The DC and AC conductivities show some features of the microstructure. Anomalies in the DC conductivity at ∼ 570 K–900 K are indicative of a change in conduction which is tentatively assigned primarily to the formation of nuclei of the cubic γ-Li 2TiO 3 phase in this temperature region, well below the first order phase transition β → γ at 1425 K–1485 K.

High-sensitivity fast neutron radiography system

Introduced in this paper is a fast neutron radiography system, which is mainly composed of a scintillation fiber array and a scientific grade optical CCD. The 14 MeV neutrons produced by deuterium-tritium fusion reactions, penetrate through objects and fall into a 50 mm×50 mm scintillation fiber array, and the neutron radiation is converted to green light (496 nm). The array has a length of 100 mm, consisting of 100×100 square scintillation fibers each with a cross-section of 500 μm×500 μm. For 14 MeV neutrons, the detection efficiency is as high as 21.4%. To avoid direct radiation from neutrons, the CCD is coupled to the array by a mirror and lens optics. By taking into account the factors affecting image quality, the resolution is estimated to be 1.5 mm. Several neutron radiographs have been obtained successfully in experiments carried out on K400 neutron generator.

Fast Fission Assisted Ignition of Thermonuclear Microexplosions

It is shown that the requirements for fast ignition of thermonuclear microexplosions can be substantially relaxed if the deuterium-tritium (DT) hot spot is placed inside a shell of U-238 (Th-232). An intense laser - or particle beam-projected into the shell leads to a large temperature gradient between the hot DT and the cold U-238 (Th-232), driving thermomagnetic currents by the Nernst effect, with magnetic fields large enough to entrap within the hot spot the α-particles of the DT fusion reaction. The fast fission reactions in the U-238 (Th-232) shell implode about 1/2 of the shell onto the DT, increasing its density and reaction rate. With the magnetic field generated by the Nernst effect, there is no need to connect the target to a large current carrying transmission line, as it is required for magnetized target fusion, solving the so-called “stand off” problem for thermonuclear microexplosions. - PACS number: 28.52.-s.

Thermonuclear plasma with autocatalytic thermomagnetic current amplification by nuclear reactions from fusion neutrons

It is proposed to use the neutrons released from a deuterium-tritium or deuterium-deuterium fusion reaction to drive thermomagnetic currents in a plasma corona surrounding the fusion plasma through the heating of the corona with nuclear reactions by the neutrons released in the fusion reaction. Because the neutron reaction cross sections are larger for slow neutrons, it is proposed to slow them down in a moderator separated from the hot plasma of the corona, giving the configuration a striking similarity to a heterogeneous nuclear fission reactor. While in a fission reactor the separation makes possible a growing neutron chain reaction, it here makes possible the autocatalytic amplification of the thermomagnetic currents by an increase of the fusion reaction rate through a rise of the plasma pressure by the magnetic pressure of the thermomagnetic currents. This is expected to substantially increase the nτ product over its Lawson value.

Fusion–fission–fusion fast ignition plasma focus

A crucial advancement in the problem for the controlled release of energy by nuclear fusion appears possible by an autocatalytic fusion–fission–fusion microexplosion, where the deuterium–tritium (DT) fusion reaction of a dense magnetized DT plasma placed inside a thin liner made up of U238, Th232 (perhaps B10) releases a sufficient number of 14 MeV fusion neutrons which by fission reactions in the liner implode the liner on the DT plasma. The liner implosion increases the DT plasma density and with it the neutron output accelerating the fast fission reactions. Following the fast fission assisted ignition, a thermonuclear detonation wave can propagate into unburnt DT to reach a high gain. The simplest way for the realization of this concept appears to be the dense plasma focus configuration, amended with a nested high voltage magnetically insulated transmission line for the heating of the DT. The large magnetic field needed for the α-particle entrapment of the DT fusion reaction is here generated by the thermomagnetic Nernst effect, amplifying the magnetic field of the plasma focus current sheet.

Studies of burning plasma physics in the Joint European Torus

In burning plasma experiments, the very energetic alpha (α) particles resulting from a deuterium–tritium fusion reaction will be the dominant heating mechanism and will give rise to new physics issues. Recent experiments performed on the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] and aiming to investigate burning plasma physics are reported in this paper. In the presence of very energetic particles, the magnetohydrodynamic stability of plasmas is affected. Sawteeth will be strongly stabilized and may lead to the onset of neoclassical tearing modes (NTMs), which are damaging for the plasma confinement. 4He ions injected at 120 keV by the neutral beam injection system and accelerated by ion cyclotron resonance frequency (ICRF) waves to the MeV energy range have provided the necessary energetic particles to investigate these effects. New scenarios have been used in order to control the stability of the sawteeth even in the presence of fast particles and to prevent or delay the appearance of NTMs. Finally, in a plasma self-heated by α-particles, the thermal stability is a critical point and equilibrium will have to be maintained between the α-heating and the transport losses. Experiments have been performed where a fraction of the ICRF heating has been used to simulate the α-heating. A situation of thermal runaway has been demonstrated and successfully controlled.

Helium Production Due to Neutron Streaming through Small Circular Ducts in a Fusion Reactor Blanket by Analytical Fitting from Monte Carlo Calculation Results

The neutron streaming through a small circular duct in a shielding blanket module in the deuterium-tritium (DT) fusion reactor was evaluated, and the helium production at a plug of the cooling water branch pipe was calculated by a three-dimensional Monte Carlo method. By changing systematically the duct diameter, the blanket thickness, and the boron content in the plug, analytical representations of the helium production could be obtained as functions of these parameters based on the Monte Carlo results. Their dependencies on the blanket composition could also be clarified. The analytical formulas thus obtained were applied to clarify the shielding design condition required to satisfy the shielding design criteria for a DT fusion reactor.

Tritium Confinement Demonstration Using Caisson Assembly for Tritium Safety Study at TPL/JAERI

ABSTRACTIn order to demonstrate tritium confinement performance in DT (deuterium-tritium) fusion reactors at any accident, TPL/JAERI has carried out intentional tritium release experiments using Caisson Assembly for Tritium Safety study (CATS). Some data have been accumulated such as actual tritium behavior in the normal ventilated area and response of tritium monitors and emergency isolation valves. The experimental results of confinement of released tritium of about 3 GBq in 12m3 of the Caisson under ventilation of 50 m3/h were consistent with those of simulation by a three dimensional eddy flow calculation code modified from FLOW-3D. Using this simulation code, the tritium confinement performance in large rooms can be demonstrated for actual fusion reactors.

Neutron emission study of DT plasmas heated with tritium neutral beams

The neutron emission energy spectrum from deuterium–tritium fusion reactions has been measured in experiments carried out at the Joint European Torus for plasmas heated with high power neutral beam (NB) injection of tritium beams at Eb≈150 keV using a magnetic proton recoil neutron spectrometer. High quality data were obtained in which up to three spectral components due to different ion reactions could be distinguished with the help of dedicated model calculations of the fusion neutron emission based on Monte Carlo simulations. The analysis model involved neutrons from reactions of NB ions on passing and trapped orbits interacting with thermal bulk ions. Moreover, a narrow Gaussian component, due to neutrons from thermal d+t→α+n reactions, could be resolved in some cases. Results are presented and the plasma information obtained is discussed as an illustration of the capabilities of neutron emission spectroscopy diagnostics.

Tritium Production Rate and Tritium Breeding Ratio: A Comparative Study of Li2O and Lithium Assemblies with Different Concentrations of 6Li

In view of the blanket design of a futuristic deuterium-tritium fusion reactor, a time-dependent study of 14-MeV neutrons has been carried out in bare lithium and Li2O blanket assemblies with different concentrations of 6Li nuclei. For assemblies of different sizes, time-dependent total neutron fluxes, a tritium production rate (TPR), and a tritium breeding ratio (TBR) up to 40% concentration of 6Li (natural concentration being 7.42 at.%) have been reported. A multigroup diffusion equation and eigenfunction expansion method has been used. This study shows that for any concentration of 6Li, the values of TPR as well as TBR are higher for a Li2O assembly than those obtained for all corresponding (of same size) assemblies of lithium. However, for a given assembly of lithium or Li2O, the TBR values do not show any observable change with 6Li concentration beyond ~40%. Further, for any concentration, the values of TPR and TBR decrease substantially in both types of systems as the side of the cubic assembly is reduced from 1 to 0.5 m.

Isotope Effect in Cryosorption of Tritium to Molecular Sieves and Activated Carbon at 77 K

The tritium bred in a deuterium-tritium fusion reactor is removed from its blanket by using helium sweep gas mixed with some amount of hydrogen to promote the release rate. From the viewpoint of uptake capacity at the partial pressure of tritium and ease of tritium transfer to the main fuel cycle, a cryosorption bed, which uses molecular sieves or activated carbon at the liquid nitrogen temperature, is attractive for recovery of bred tritium in the blanket sweep gas. The cryosorption bed is also applicable as a transfer pump of tritium in the fuel-handling process. Tritium cryosorbed from a certain subunit of the fuel-handling system is transferred to other subunits by an increase in temperature and the operation of valves. It is necessary to know the adsorption isotherm and the mass transfer coefficient of each hydrogen isotope for estimation of breakthrough performances of tritium in a cryosorption bed because the mixture of tritium with other hydrogen isotopes must be treated. It is observed that the isotope effects in adsorption capacity and surface diffusivity have a close connection with the quantum effect that is represented by the reduced molecular weight. The correlative equation between Langmuir constants in the adsorption isotherm with reduced molecular weight of hydrogen isotopes is proposed. The correlative equation between surface diffusivity and reduced molecular weight is also presented.

Transients in D-T and D-3He Tokamak Fusion Reactors

A time-dependent, volume-averaged particle and power balance code is used to investigate reactivity transients during tokamak startup and after sudden changes in the plasma confinement, fueling rates, and impurity concentrations in deuterium-tritium (D-T) and D-3He fusion reactors. For a given H-mode factor fH relative to the ITER89-P scaling law, a very narrow range of values, limited by quenching of the fusion burn due to ash accumulation and by exceeding operational limits, is found to sustain steady fusion burn. The dependence of the large power overshoot taking place shortly after ignition due to ash accumulation on the assumed ρ and fH is examined. To alleviate the excessive external heating power requirements for D-3He-reactor startup, schemes utilizing D-T fusion reactions are considered. Because of power transients of several hundreds of megawatts in reactors operating at a gigawatt level of fusion power, triggered by very small changes in the plasma confinement (

The Impact and Status of Neutron-Activation Cross Sections for Short-Lived Reaction Products of Interest in Fusion Reactor Design

The impact and status of the cross sections for production of short-lived radioactivities in the intense high-energy neutron fields associated with deuterium-tritium fusion reactors is investigated. The main concern relative to these very radioactive species is that they may represent enhanced radiation sources not accounted for in typical transport calculations. These enhanced radiation sources may affect heat removal and shielding requirements. The status of nuclear data required to assess these issues is surveyed. Among the factors considered in defining the relevant reactions and setting priorities are quantities of the elemental materials in a fusion reactor, isotopic abundances within elemental categories, the decay properties of the induced radioactive by-products, the reaction cross sections, and the nature of the decay radiations. Attention has been focused on radioactive species with half-lives in the range from ~1 s to 15 min. Available cross-section and reaction-product decay information from the literature are compiled and examined. The evaluated data sets are collapsed using neutron spectra from three fusion reactor designs - ARIES I and II and the International Thermonuclear Experimental Reactor (ITER). The group-averaged cross-section sets are then used to produce neutron-spectrum-averaged, one-group cross sections, which are, in turn, used to produce decay heating reaction rates for each of the reactions. The decay heating rate is used as a measure of the radiation source strength associated with a given reaction. The decay heating reaction rates are compared against neutron heating reaction rates. Calculated decay heat to neutron heating ratios are required to be >10% in order for the reaction to be considered of importance for further study. The reactions of importance are identified as 28Si(n,p)28Al, with a ratio of ~10%, and 207Pb(n,n’)207mPb, with a ratio >50%. The 28Si(n,p)28Al reaction could affect heat removal requirements for reactors employing silicon carbide as a structural material. The 207Pb(n,n’)207mPb reaction could affect heat removal and shielding requirements for shield designs employing lead. Identified reactions of slightly less importance are 27Al(n,p)27Mg, 9Be(n,α)6He, 52Cr(n,p)52V, 16O(n,p)16N, and 204Pb(n,2n)203mPb - all of which have ratios between 1 and 4%.

Neutronics Analysis of the International Fusion Materials Irradiation Facility High-Flux Test Volume

The purpose of the International Fusion Materials Irradiation Facility (IFMIF) is to provide irradiation conditions of a typical deuterium-tritium (D-T) fusion reactor for small material samples, but with higher irradiation levels. An extensive code and data development has been performed, allowing a comprehensive neutronic analysis of the high-flux test volume. New data evaluations for neutron interactions and responses at high energies (20 to 50 MeV) were performed and processed, and a Monte Carlo neutron source model for the Li(d,xn) reaction was developed for use with the MCNP neutron transport code.The neutron flux density was found to be >1014 n·cm-2·s-1 throughout the anticipated high-flux test volume with a high-energy fraction (>14 MeV) of ~20%. The available test volume with >20 dpa/full-power year in iron was found to be 550 ± 180 cm3. This uncertainty is due almost entirely to the uncertainty in the total neutron yield. Hydrogen and helium production rates were calculated and a helium/dpa ratio between 10 and 12 appm/dpa was found, which is similar to that found in a D-T fusion reactor. IFMIF was found to provide an adequate environment for the simulation of D-T fusion reactors, but more work is required to extend and improve the current data and tools.

Thermal Breeding of Tritium: A Comparative Study of the Li + C and 3He + C Systems

Results are reported for the space-dependent neutron spectra and tritium breeding ratio (TBR) in a proposed Li + C blanket of a deuterium-tritium fusion reactor. The multigroup diffusion equation is solved as an eigenvalue problem for three concentrations of lithium in graphite. The effect on the value of TBR of increasing the fraction of low-energy neutrons in a completely thermalized source is studied. A comparison of neutron spectra as obtained in the Li + C and 3He + C systems is also made. The results show that TBR increases with the concentration of lithium in graphite as well as with the fraction of low-energy neutrons in the source. [Essentially the same value of TBR (= 0.277) is obtained for the Li + C system with a lithium to graphite concentration of 4 x 10-2 as for a 3He + C system with a natural density of 3He.] Moreover, TBR attains an almost constant value for assembly thicknesses greater than -20 cm. Also, if a source with an increased fraction of low-energy neutrons is used, the effect is more pronounced in the 3He + C system for the range of lithium concentrations considered.

Plasma Exhaust Purification by Thermal Swing Adsorption: Experimental Results and Modeling

For several years at the Joint Research Centre-Ispra laboratories, cyclic adsorption processes have been developed for the purification of the plasma exhaust stream of a deuterium-tritium fusion reactor. A purification process consisting of two coupled thermal swing adsorption systems seemed to be the most convenient process. In this context, a screening study was carried out to select the most suitable adsorbent materials and appropriate working temperatures. This was mainly done by experimental measurements of adsorption isotherms of the single components of the plasma exhaust stream and by a careful evaluation of the multicomponent adsorption equilibria. Experiments on adsorption dynamics were carried out in a pilot plant to demonstrate the feasibility and to evaluate the performance of the process. The experimental apparatus was designed to treat gas mixture flow rates up to 20 to 30 standard temperature and pressure l/h. A mathematical model was developed and tested against the experimental results to describe the adsorption process and, in particular, to evaluate and to optimize the process cycle time. 27 refs., 4 figs., 9 tabs.

Mass Transfer Coefficients in Cryosorption of Hydrogen Isotopes on Molecular Sieves or Activated Carbon at 77.4 K

The tritium bred in a deuterium-tritium fusion reactor is removed from its blanket by using helium sweep gas. From the viewpoint of adsorption capacity and pressure of tritium at release, a cryosor...

The effect of neutron energy on defect production in alumina

In a deuterium-tritium fusion reactor, neutrons are produced at an energy of about 14 MeV. When these neutrons and other lower energy neutrons from (n, xn) reactions travel through insulating materials in the reactor, displacement damage will occur. Using the Monte Carlo code, TRIM (Transport of Ions in Matter), calculations using aluminum (Al) and oxygen (O) ions at energies that simulate expected recoil energy levels in alumina (Al 2O 3) were performed. This study focuses on recoil energies ranging from 100 eV to 10 MeV. In addition, recoil energy spectra for Al and O were calculated for 1 MeV and 14 MeV neutrons using the computer code, SPECTER. Combining the TRIM and SPECTER calculations, it was possible to determine the number of aluminum and oxygen vacancies created in alumina resulting from a specific neutron energy.

Performance characteristics of a compact D-T neutron generator system

A new pulsed neutron generator system has been introduced which uses the deuterium-tritium fusion reaction to produce 14 MeV neutrons. The new system incorporates the latest technology in its electronics, sealed tube neutron head and computer control. The system is extremely flexible and adaptable to a wide range of applications in the field of materials non-destructive analysis.

Study on a Method to Recover Tritium from Blanket Sweep Gas

The tritium bred in a deuterium-tritium fusion reactor is to be extracted from the tritium breeding blanket by sweep gas. To be used as fuel for the reactor, the tritium must be recovered in a form that is easy to transfer to the main fuel cycle. The feasibility of a cryosorption method that uses a porous adsorbent, such as molecular sieves or activated carbon, at liquid nitrogen temperature (77.4 K) is discussed.