Showing papers in "Fusion Science and Technology in 1984"

Importance estimation in forward Monte Carlo calculations

Abstract: A method for estimating the importance function in forward Monte Carlo particle transport calculations is described. The importance function is estimated for every region of phase-space. Although subject to statistical fluctuations, the estimated importance function has proven to be a very valuable tool for selecting variance reduction parameters. Some deep penetration calculations are included to demonstrate applicability.

Lower Activation Materials and Magnetic Fusion Reactors

Abstract: Radioactivity in fusion reactors can be effectively controlled by materials selection. The detailed relationship between the use of a material for construction of a magnetic fusion reactor and the material's characteristics important to waste disposal, safety, and system maintainability has been studied. The quantitative levels of radioactivation are presented for many materials and alloys, including the role of impurities, and for various design alternatives. A major outcome has been the development of quantitative definitions to characterize materials based on their radioactivation properties. Another key result is a four-level classification scheme to categorize fusion reactors based on quantitative criteria for waste management, system maintenance, and safety. A recommended minimum goal for fusion reactor development is a reference reactor that (a) meets the requirements for Class C shallow land burial of waste materials, (b) permits limited hands-on maintenance outside the magnet's shield within 2 days of a shutdown, and (c) meets all requirements for engineered safety. The achievement of a fusion reactor with at least the characteristics of the reference reactor is a realistic goal. Therefore, in making design choices or in developing particular materials or alloys for fusion reactor applications, consideration must be given to both the activation characteristics of amore » material and its engineering practicality for a given application.« less

Blanket Design and Calculated Performance for the Lotus Fusion-Fission Hybrid Experimental Devices Test Facility

Abstract: The first in a series of fusion-fission hybrid blanket assemblies to be tested in the LOTUS test facility at the Swiss Federal Institute of Technology in Lausanne (EPFL) is described. The aim of the EPFL program is to conduct integral neutronic benchmark experiments with design features resembling genuine blanket design approaches. The assembly described here simulates fission-suppressed thorium blankets of the type used in direct enrichment hybrid designs. The neutronic studies on which the design is based are described in detail.The blanket assembly is a parallelepiped 85 cm thick, 100 cm high, and 140 cm wide. It is to be placed in front of a Haefely sealed neutron generator with an intensity of 5 × 1012 14-MeV neutron/s. It consists of a 2-mm-thick stainless steel sheet simulating the first wall, followed by a 100-mm-thick lead plate for neutron multiplication, a 35-mm-thick spectrum adjustment zone of lithium carbonate blocks encased in aluminum, a 277.2-mm-thick fissile breeding zone of alum...

Fast Hybrid Thermionic Blankets with Actinide Waste Fuel

Abstract: Basic performance analyses of a fast thermionic blanket driven by a deuterium-tritium fusion reactor with a wall loading of 2.25 MW/m/sup 2/ (10/sup 14/ incident neutron/cm/sup 2/s) is discussed. The basic thermionic element has been evaluated with some modifications from the German Incore-Thermionic-Reactor Project. During this study, highly enriched UO/sub 2/ fuel is replaced by the following actinide waste materials: /sup 244/CmO/sub 2/, (/sup 241/AmO/sub 2/ + /sup 243/AmO/sub 2/) corresponding to the isotopic composition of the nuclear waste materials produced in light water reactors, natural UO/sub 2/. The calculated high emitter heating values P for converters with /sup 244/CmO/sub 2/ as nuclear fuel are adequate for efficient thermionic conversion, P > 90 W(thermal)/ cm/sup 2/. Those values with AmO/sub 2/ fuel are also still in the range of interest (P > 40 to 50 W(thermal)/ cm/sup 2/) whereas they are rather low for thermionic hybrid blanket with natural uranium (P = 15 to 20 W(thermal)/cm/sup 2/).

Space-Dependent Analysis Plasma Engineering of Feedback Control to Suppress Thermal Runaway by Compression-Decompression

Abstract: Feedback stabilization of the thermal runaway by compression-decompression is studied by using a one-dimensional transport model that includes the effect of plasma profiles. The stability conditions required for the control system are derived from an eigenvalue analysis. The dynamic responses of plasma parameters to the control are also studied numerically by time integrating the transport equation with locally perturbed initial conditions. The stability conditions on the feedback control system are similar to previous results obtained from the zero-dimensional analysis. Time-dependent analysis shows that thermal runaway initiated by the local disturbances of temperature is suppressed, allowing a stationary burn of the space-dependent plasma.

Proportional-Integral Control Modes for a Hydrogen Isotope Distillation Column

Abstract: The dynamics and control of a hydrogen isotope distillation column are discussed. The proportionalintegral (PI) controller parameter setting method previously reported by one of the authors is further investigated and extended by applying the method to two different experimental control modes. The method accounts for the nonlinearity of the column to some extent and allows us to predict the unstable region or the region of the proportional-only control behavior. The method can also be applied to the cases where the measurement of the controlled variable is accompanied by a significant time lag. The mean delay time depends greatly on the controlled variable and manipulated variable chosen and the upset condition assumed, varying by over two orders of magnitude. The PI control presents great stability, and a rather long time lag is permissible in the measurement of the controlled variable if the flow rate of the top product is chosen for the manipulated variable. On the other hand, if the reflux ratio is manipulated for controlling the lightest key element in the bottom product, the great stability is no longer present and the time lag must be adequately short. Once several response curves of the controlled variable are calculated for differentmore » magnitudes of the manipulated variable upset, the parameter setting method proposed makes it possible to study how long a time lag is allowable in the measurement of the controlled variable.« less

Canadian Experience with Tritium—The Basis of a New Fusion Project

Abstract: Fusion power stations using the deuterium-tritium reaction will have substantial inventories of tritium in the oxide, molecular, and solid (metal hydride) forms. A new Canadian fusion engineering p...

Future Technology Requirements For Magnetic Fusion-An Evaluation Based On Conceptual Design Studies

Abstract: The future technology requirements for magnetic fusion have been identified from an assessment of the conceptual design studies that have been performed. A summary of worldwide conceptual design effort is presented. The relative maturity of the various confinement concepts and the intensity and continuity of the design efforts are taken into account in identifying future technology requirements. A major conclusion of this study is that there is a high degree of commonality among the technology requirements identified for the various confinement concepts.

The Materials Impact on Fusion Reactor Safety

Abstract: Seven potential safety concerns for deuteriumtritium fusion reactors were examined and the influence of blanket material choice determined. This influence was quantified in terms of relative consequence indices (RCIs) according to prescribed consequence criteria.Selected combinations of structural material (Type 316 stainless steel, HT-9, vanadium alloy, or TZM), primary coolant (pressurized water, helium, lithium, or flibe), and tritium breeder (LiAlO2, lithium, or Li17Pb83) were examined. The analyses and indices were structured to focus on the specific material properties that influence the results, which allows for comparison of materials not included in the present study.The safety concerns that were found to be relatively insensitive (differing by less than an order of magnitude) to material choice are the rate of temperature increase from continued plasma heating following loss of coolant and electromagnetic effects of plasma disruptions. The range of the RCIs was about an order of magnitud...

Radiation Streaming Analysis for The Beam Ports of the Laser Fusion Reactor, Senri-I

Abstract: Three-dimensional Monte Carlo analyses are performed for the three-legged beam ports of the laser fusion reactor SENRI-I. The validity of two devices for attenuating neutron flux is examined, and it is shown that the fast neutron flux attenuation of 1.4 X 10/sup 5/ can be reached by adopting these two devices in combination. The effectiveness of variance reduction techniques is also examined. It is determined that path length stretching is useful for neutron groups above 1 MeV. Adopting adjoint flux-dependent Russian roulette weight cutoff also seems useful.

Implications of Polarized Deuterium-Tritium Plasmas for Toroidal Fusion Reactors

Abstract: Spin polarization of the plasma deuterons and tritons in a magnetic fusion reactor can result in an increase in the fusion reactivity and variation of the angular distribution of emission of the fu...

Monte Carlo Studies of the Ion Cyclotron Range of Frequencies in Tandem Mirrors

Abstract: A simulation code for studying the effect on tandem mirror plasmas of waves in the ion cyclotron range of frequencies has been developed This code utilizes Monte Carlo techniques to model coulomb

System studies for a quasi-steady-state advanced physics tokamak

Abstract: Parametric studies were conducted using the Fusion Engineering Design Center (FEDC) Tokamak Systems Code to investigate the impact of variation in physics parameters and technology limits on the performance and cost of a low q{sub {psi}}, high beta, quasi-steady-state tokamak for the prupose of fusion engineering experimentation. The features and characteristics chosen from each study were embodied into a single Advanced Physics Tokamak design for which a self-consistent set of parameters was generated and a value of capital cost was estimated.

A Fundamental Study of Cryopumping Systems with Charcoal Sorption Panel

Abstract: A fundamental study of cryopumping of a charcoal sorption panel with a refrigerator was performed aimed at applications in nuclear fusion experiments. Typical pumping speeds at the cryopanel temperature of 10.4 K for hydrogen, helium and argon were obtained as 3.5 x 10/sup -1/, 1.6 x 10/sup -2/ and 1.0 m/sup 3//s, respectively, in the range of throughout less than 1 x 10/sup -4/ Pa.m/sup 3//s. The pumping speed was found to increase linearly on a semilogarithmic plots with the inverse of adsorption temperature. The activation energy of hydrogen capture on the charcoal was estimated between 100 J/mol to 240 J/mol, which is nearly equal to the heat of fusion of hydrogen. Several experiments to improve cryopumping performance were also carried out by modification of the shape of the cryopanel, and by evaporation of titanium onto the panel and etc.

Investigations of High-Energy Deuterons in a Dense Plasma Focus Device by Means of Neutrons Emitted in the 7Li + D Process

Abstract: A study of the high-energy part of the deuteron spectrum produced by the Frascati 1-MJ plasma focus device is carried out through measurements of (a) the energy distribution of prompt neutrons emit...

Tokamak fusion reactors with less than full tritium breeding

Abstract: A study of commercial tokamak fusion reactors with tritium concentrations and tritium breeding ratios ranging from full deuterium-tritium operation to operation with no tritium breeding is presented The design basis for these reactors is similar to those of STARFIRE and WILDCAT Optimum operating temperatures, sizes, toroidal field strengths, and blanket/ shield configurations are determined for a sequence of reactor designs spanning the range of tritium breeding, each having the same value of beta, thermal power, and first-wall heat load Additional reactor parameters, tritium inventories and throughputs, and detailed costs are calculated for each reactor design The disadvantages, advantages, implications, and ramifications of tritium-depleted operation are presented and discussed

Compositional Changes in Surface Region of Sic Single-Crystal Due to Hydrogen and Helium Ion Irradiation

Abstract: Compositional changes in the surface region of single-crystal SiC(0001) due to heat treatment and light ion irradiation in the keV range were studied with the use of AES. The heat treatment at 1000/sup 0/C formed a carbon enriched layer with a thickness of 20 A on the top surface and a carbon depletion layer below this layer. Both hydrogen and helium ion irradiation caused depletion of silicon atoms in the near surface region and depletion of carbon atoms in the deeper surface region. TRIM computations revealed that in the process of slowing down of incident hydrogen ions, their kinetic energy was transfered preferentially to silicon atoms in the near surface region and to carbon atoms in the deeper surface region. This tendency explains the formation of each altered layer.

Reliability Analysis of the Emergency Power Supply System of the Starfire Tokamak

Abstract: Early attention to safety will ensure that the potential safety advantages of fusion are realized. Reliability analysis techniques are applied to a major safety system, the emergency power supply system, using the STARFIRE design as an example. The median failure probability of this system is found to be 2 X 10/sup -6/ at shutdown, with an error factor of 5. This is comparable with the reliability of similar systems in existing fission power stations.

Importance Function Biasing of the Deep Penetration Monte Carlo Calculation

Abstract: The formal basis of the use of calculated importance information for biasing forward and adjoint Monte Carlo deep penetration sheilding problems is presented. The distinction between the ''point value'' and ''event value'' functions for adjoint problems is discussed. The analysis reveals that the emergent particle density, and not the particle flux density, is the proper choice of biasing function for the selection of the adjunctor's next collision site. This is analogous to the choice of the event value as the value function for the biased selection of the next collision site in the forward analysis. A numerical illustrative problem consisting of a concrete cylinder with an axial duct, a plane source on the bottom surface, and four joint detectors outside the emergent top surface is used to demonstrate this theory.

Radiation Streaming in Penetrations of Taska

Abstract: The procedure used in setting the first wall and shield of the end cell of the TASKA tandem mirror test facility is presented. This is followed by calculations to provide radiation sources at the neutral beam injector (NBI) penetrations. Representative NBIs are modeled and radiation problems analyzed.

Chemical Shift of Graphite Basal Face Due to keV-Deuterium Bombardment

Abstract: Trapping and release of deuterium at a pyrolytic graphite basal face are studied by using X-ray photoelectron spectroscopy. The trapped deuterium density in nearly 10 atomic layers of the surface is estimated through measurement of C ls positive shift due to C-D bond formation. Most of the deuterium atoms trapped in the graphite to saturation at room temperature are not released by the heat-treatment at up to 450/sup 0/C. The trapped-deuterium density is found to reach a lower equilibrium value by the bombardment to saturation at above 180/sup 0/C than those by the bombardment at below 180/sup 0/C. The equilibrium trapped-deuterium density decreases down to one third, as the target temperature is raised above 180/sup 0/C to 430/sup 0/C. The decrease in the equilibrium trapped-deuterium density at above 180/sup 0/C is explained by the ion-induced re-emission of the deuterium.

Improvement of the Two-Temperature Radiative Transport Model

Abstract: The frequency dependence of a thermal radiation field complicates the computation of radiative energy transport in optically thin media because the spectrum may be uncoupled from local thermodynamic conditions. A model for combining the effect of the frequency dependence into a radiation temperature chosen to represent the temperature of both local and nonlocal emitting regions is described. The derived equations are much easier to solve than the frequencydependent equations and can be applied to a broad class of problems. The equations are used to investigate the response of a gas in an inertial confinement fusion (ICF) reaction chamber to target explosions. The response is compared for ambient densities of 1.77 x 10/sup 18/ and 1.77 x 10/sup 17/ atom/cm/sup 3/. The error in using the brightness temperature instead of a color temperature to evaluate the opacities is illustrated. An analytic analysis shows the cooling wave observed from energy releases > 10/sup 18/ erg will not occur in an ICF cavity. This is confirmed by the numerical calculations.

Transport of beryllium-7 in a lithium loop

Abstract: A /sup 7/Be transport test was performed in the Beryllium-7 Experimental Lithium Loop with hot leg at 270/sup 0/C and cold leg at 230/sup 0/C. The ''cold leg'' test stringer was in a rising temperature region at 250/sup 0/C. A total of 108 test coupons were included in the material compatibility and deposition test programs, containing AISI Types 304 and 304L stainless steels, Fe-2 1/4 Cr1 MO, pure iron, molybdenum, beryllium, zirconium, titanium, yttrium, three different aluminide coatings on Type 304 stainless steel substrates, and both tubular and flat butt-welds of Type 304 stainless steel. An average lithium velocity of 1.36 m/s was established during the test which was terminated after 3718 h. The /sup 7/Be activity data indicated that the deposition of /sup 7/Be is a function of temperature. The cold leg positions displayed maximum /sup 7/Be deposition followed by the intermediate temperature locations (cold leg test stringer) and the hot leg locations. Two chemical forms of /sup 7/Be are expected in lithium, namely, unbonded /sup 7/Be at a low concentration, and a fine precipitate of /sup 7/Be/sub 3/N/sub 2/ at a high concentration. The deposit in the hot leg region is presumed to be primarily /sup 7/Be, whilemore » the cold leg deposit is mostly /sup 7/Be/sub 3/N/sub 2/. The cold leg specimens of a given material showed more /sup 7/Be deposition than the hot leg specimens of the same material, consistent with the /sup 7/Be activity data on the piping. Based on the present investigations and previous data, it is concluded that /sup 7/Be produced in the Fusion Materials Irradiation Test (FMIT) facility will have sufficient nitrogen in the lithium system to form /sup 7/Be/sub 3/N/sub 2/. It is expected that the majority of /sup 7/Be will be transported to the colder parts of the loop and deposited as /sup 7/Be/sub 3/N/sub 2/. However, a small amount of /sup 7/Be in the unbonded form will be in the hotter parts of the loop and is expected to diffuse into the steel piping.« less