Masao Ohta

Nuclear Characteristics of D-D Fusion Reactor Blankets, (I) Survey Calculation

In this paper, neutronic and photonic calculations are undertaken covering several blanket models of the D-D fusion reactor, using presently available data, with a view to comparing the nuclear characteristics of these models, in particular, the nuclear heating rates and their spatial distributions. Nine models are taken up for the study, embodying various combinations of coolant, blanket, structural and reflector materials. About 10 MeV is found to be a typical value for the total nuclear energy deposition per source neutron in the models considered here. The realization of high energy gain is contingent upon finding a favorable combination of blanket composition and configuration. The resulting implications on the thermal design aspect are briefly discussed.

Effects of nuclear elastic scattering on ignition and thermal instability characteristics of D-D fusion reactor plasmas

Nuclear elastic scattering is included in the analysis of ignition condition and thermal instability in pure and catalysed D-D fusion reactor plasmas. Nuclear-elastic-scattering events take place, to some extent, during the slowing-down of energetic fusion products and enhance the heating of the background ions. The inclusion of this effect relaxes the minimum of the confinement requirement for self-sustained D-D plasmas by about 15%. It enhances, however, the thermal instability of the plasma, leading to an increase in the critical temperature.

Time dependent multigroup analysis of nuclear elastic scattering effects in advanced fuel fusion plasmas

Effects of nuclear elastic scattering (NES) on the slowing down of charged fusion products in a typical deuterium plasma and the burn dynamics of ignited Cat-D and D-D-3He plasmas are investigated on the basis of a linear Boltzmann-Fokker-Planck equation. A multigroup method is used to obtain the distribution functions for the fusion products and their recoils. It is shown that an adequate treatment of the slowing-down process, especially the consideration of NES and of the slowing-down time delay, is essential for an accurate prediction of the dynamic behaviour and the thermal instability of plasmas. NES enhances the thermal instability and accelerates the temperature excursion from the equilibrium. The inclusion of NES results in a 20-30 keV increase in the critical temperature for thermal stability.

Nuclear characteristics of D-D fusion reactor blanket. II. Thermal blanket and blanket-shield designs.:Thermal Blanket and Blanket-Shield Designs

The nuclear characteristics of the thermal blanket and blanket-shield designs are analyzed to provide a basis for optimizing the blanket design of D-D fusion reactors. The thermal blanket is devise...

Calculational Method for Neutron Heatingin Dense Plasma Systems, (II) Application to Burning D-T Pellets.:Application to Burning D-T Pellets

The effect of neutron heating on the burn characteristics of inertial confinement fusion pellets is investigated by applying the calculational method developed in an earlier paper (Part I). The basic equations are time-dependent transport equations for fusion neutrons and recoil ions, being written in terms of the modified Eulerian coordinates originally proposed by Wienke (1974). After incorporating these equations into the one-dimensional hydrodynamics code MEDUSA, burn simulations are made for isobaric D-T pellets models compressed to 1,000 times the liquid density. It is found that in reactor-grade pellets, the inclusion of neutron heating decreases the fuel gain from the values obtained by neglecting the neutron heating

Boiling detection experiments by acoustic analysis applying linear discriminant function

Abstract The detection of the boiling is examined by acoustic analysis applying the pattern recognition technique. The subcritical assembly was used as a sham reactor vessel. The vapor bubbles at the surface of the stainless steel heater generate the sound when they vanish in the subcooled water. These sound are detected by the hydrophone and then transformed to the power spectral densities(PSD). The theory of linear discriminant function is applied to classify the PSD data. The generation of the boiling is detected by the computer which distingwish the PSD with boiling sound from that without boiling sound. The accuracies of discriminations were very high when the PSD of 2 to 6 KHz range were discriminated in these experiments.

Fuel Cycle Characteristics of D-T Fusion Reactor and Base-Satellite System

The fuel-cycle characteristics are presented for the D-T fusion reactor and for the base-satellite fusion reactor system. The latter is a combination consisting of D-T base reactor and D-3He satellite reactors, which offers the potential advantage of considerable flexibility in meeting our expanding energy needs. For the D-T fusion reactor, the fuel-self-sufficiency condition and doubling time are determined with account taken of fuel separation efficiencies. It is found that differences in the fuel separation efficiency for the plasma waste gas, in particular, appreciably influence the conditions of fuel-self-sufficiency and the doubling time. To satisfy the fuel-self-sufficiency condition, the efficiency must attain 97–99.% or so. For the base-satellite system, calculations are presented for various combinations of this system and for different system parameters such as critical support ratio (maximum allowable ratio between base and satellite reactor power outputs), tritium stockpile inventory, neutron...

Neutronics Calculations for Gas-Suspended Boron Carbide Cooling D-D Fusion Reactor Blankets

An examination is made of the dependence shown by the nuclear characteristics of a D-D fusion reactor blanket cooled by particles of boron carbide (B4C) suspended in gas, on the design variations such as 10B enrichment in B4C and the B4C concentration in the coolant channel. The results of calculation reveal that the flow of B4C particles containing 10B with the natural abundance and loaded to the maximum attainable concentration is an optimal choice as coolant in terms of nuclear characteristics: the blanket cooled by the flow exhibits the maximum nuclear heating, the minimum neutron energy leakage and the minimum induced activity. The flow also would have the advantage of the lowest cost on account of no need of additional processing to enrich or deplete 10B.

A method of analysis of neutron inelastic scattering by heavy nuclei and its application to cross section evaluation for Th-232

Abstract In an effort to resolve the apparent discrepancies between the measured and calculated inelastic scattering cross sections as well as among different evaluations for actinide nuclei, a method of analysis has been proposed which enalbles calculation of the inelastic scattering caross section taking into account both the direct and compound-nuclear processes. The coupled-channel and Hauser-Feshbach medels were combined in a consistent manner by employing Satchlers generalized transmission coefficient for the entrance channel. The neutron transmission coefficient calculated with the spherical optical model was used for the exit channels. This approximation greatly simplified the calculation and was found to give good results in the anlaysis of neutron inelastic scattering by heavy nuclei. This method has been applied to cross section evaluation for th-232.

Nuclear Design of Heliotron Fusion Reactor Blankets

A study is made of the nuclear characteristics of blanket designs intended for a heliotron fusion reactor that employs an 1=2 helical heliotron field and no toroidal coils. The blankets in front of the superconducting magnet (shielding blankets) are utilized for neutron shielding, and the other blanket regions (breeding blankets) for tritium breeding. A number of notable features inherent in this blanket concept are revealed: The stipulated tritium breeding ratio could be attained in the breeding blanket by utilizing lithium lead (Li7Pb2) as breeding material and helium as coolant, with a breeding zone thickness of 1 m. The shielding blanket should pose more difficult problems in satisfying the adopted design criteria: Holding the total blanket thickness to within the stipulated limit of 1 m would necessitate the incorporation of expensive material (e. g., W or Ta) in the blanket. The final choice between (a) thus enhancing the attenuating power of the material and (b) relaxing the limitation on blanket t...