The possibility eliminating the thermal instability of self-sustained pure and catalyzed D-D fusion reactor plasmas is examined, using the two feedback models of (a) fueling rate and (b) power control (control by power injection or subtraction). Calculations are performed on the bases of linear stability analysis and non-linear dynamic simulation.
In contrast to D-T fusion plasma, Cat. D plasma can be stabilized by fueling rate control in all the confinement time scalings adopted in the study. Pure D plasma is not completely stabilized by fueling rate control except when the confinement times are governed by trapped-ion mode (TIM) scaling. The plasma, however, can be maintained near equilibrium state even in forms of scaling other than TIM. Among the different types of fueling rate control, the one most suitable would appear to be deuterium control, in which the rate of deuterium injection is increased [decreased] to counteract temperature increase [decrease].
With power control, temperature increase [decrease] is counteracted by subtraction [addition] of power out of [into] the plasma. Compared with fueling rate control, this method exerts a more direct effect, although it involves a more complex procedure.

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Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 28 Hz, 15 Hz and 100150 Hz for low, middle and high frequency respectively. The chug-ging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude bocomes larger. As the temperature of pool water gets higher, high-frequency component of pres-sure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional motion of water column in and out of vent tubes. As the result, the characteristics of chugging phenomenon got in the experiment coulbd well be simulated. Chugging phenomenon, accompanying back flow of water into vent tubes, is a kind of low-frequency oscillation which is predominant in the pressure oscillation in the header.

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A single heater rod PWR reflood heat transfer experiments and analyses of the PWRFull Length Emergency Core Heat Transfer (PWR-FLECHT) Group I data were carried out. The objectives of the experinients and the analyses were to evaluate film boiling heat transfer coefficients in the core during reflood phase of a postulated loss-of-coolant accident in pressurized water reactors, and to provide necessary information on heat transfer correlations for development of a safety analysis computer code.
The results of these experiments showed that the film boiling heat transfer coefficients are strongly dependent upon the local subcooling at the quench front. It was found that when the subcooling at the quench front was zero, the saturated film boiling heat transfer coefficients could be expressed by a correlation similar to the Bromley correlation by introducing a representative length which is defined as the distance between the quench front and the elevation at which the coefficients are evaluated. When the subcooling at the quench front is not zero, the subcooled film boiling heat transfer coefficients could be expressed by a simple correlation. This correlation predicted that experimental results within the error band of ±20%.

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Cross section measurements were made for (n, xγ) and (n, xn) reactions of Mo, Ti and Ni at 120° with respect to the incident neutron. The monodirectional source neutrons were obtained by the associated particle method using D-T reaction. The (n, xγ) and (n, xn) data were simultaneously measured by an NE-213 scintillator using a pulse-shape dis-crimination circuit.
The (n, xγ) cross sections obtained in this paper agreed well with other experimental data. The (n, xγ) data for Ti and Ni given by Drake seem too large in the energy range beyond 4-5 MeV. Followings were pointed out for the evaluated data in the ENDF/B-IV file.
(i) The (n, xγ) cross section for Ni and the (n, xn) data for Mo are considered to be adequate.
(2) The (n, xγ) cross sections for Mo and Ni are not adequate.
(3) The (n, xn) cross sections for Ti and Ni seem to have large errors.

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A discrete ordinates transport code ENSEMBLE in (X, Y, Z) geometry has been developed for the purpose of shielding calculations in three-dimensional geometry. The code has some superior features, compared with THREETRAN which is the only code of the same kind so far developed. That is, the code can treat higher order anisotropic scattering and employs a coarse mesh rebalancing method. Moreover it has a negative flux fix-up routine using a variable weight diamond difference equation scheme and has a ray-effect fix-up option using a fictitious source based on S_N→P_N-1 conversion technique. Formulations for these advanced features in three-dimensional space have been derived.
As the demonstration of the capabilities of the code, several numerical analyses and an analysis of an annular duct streaming experiment in JRR-4 at Japan Atomic Energy Research Institute, have been performed.
As a result of these analyses, confirmation has been obtained for the prospect of applicability of ENSEMBLE to practical shielding design.

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