Making use of the variational method, an expression is derived for the upper and lower bounds of the largest eigenvalue of the one-velocity transport equation, in terms of the Rayleigh quotient. It is found that the error contained in the eigenvalue thus obtained increases or decreases in keeping with the error inherent in the trial function used for expressing the neutron flux distribution.
The first approximation for the eigenvalue and the extrapolation distances of finite cylindrical reactors are determined by using the asymptotic flux shape as trial function. The second and third approximations for the eigenvalue are derived by supplementing the asymptotic function with additional orthogonal terms.
It is proposed to combine the eigenvalue determined by the variational method with the second approximation of the flux obtained by applying the integral transport operator to the asymptotic flux. Evidence is presented to prove the convergence of an iterative procedure devised for successively applying the transport operator.
The results obtained by the above method are compared with those calculated by the flat-flux approximation, the Pi approximation and the two-dimensional SN code TWOTRAN.

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A new modified one-group diffusion scheme for one- and two-dimensional calculations ofthe gross power distribution in the BWR core is presented. The particularity of the presentmethod is that the fine distribution of the ratio between thermal and fast neutron fluxeswithin each fuel assembly is estimated analytically. Since this estimation can be performedlocally and without requiring knowledge of the fast neutron distribution, the method is quiteeffective in reducing computing time. Procedures for special treatment at the two-dimensionalcore-reflector boundaries are also derived from analytical considerations. The results obtainedfrom a series of test calculations indicate that the present method assures an accuracy almostequal to the conventional two-group calculation, and without requiring much more computingtime than the conventional one-group calculation.
The applicability of the method to three-dimensional calculations is also discussed.

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In the present paper, the performance characteristics of a liquid metal MHD inductionconverter operated with two-phase mixture flow are treated experimentally and analytically in comparison with those with single-phase liquid flow as working fluid.
The experiments were performed with a flat-linear channel induction converter, through which NaK-N2 two-phase mixture was made to flow at a velocity ranging 530m/sec, with a void fraction 050%.
Data were taken over the following range of non-dimensional parameters:
Reynolds number : 3.3×10⁴2.0×10⁵ (for liquid flow alone)
Hartmann number : 12 (with magnetic field in r.m.s. and slip S=1)
Baroczy's property index : 0.00310.023 (for two-phase flow)
The electrical power output of the experimental generator showed a sudden decrease near 20% void fraction, which was attributed to change in the flow pattern, while the generator efficiency did not show such an abrupt drop, but decreased gradually with increase of the void fraction.
Coupling the electro-magnetic equations with the power law distribution for both fluid velocity and void fraction proposed by Bankoff, we have obtained numerically the performance characteristics of the liquid metal MHD induction converter operated with two-phase flow, which provided a quite satisfactory clarification of the results obtained experimentally.

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In-pile release of fission gas from sintered UC pellets in the presence of 8230 ppm of water vapor in the He sweep gas was measured over the temperature range of 160°1, 000°C.A very complex release behavior was observed and the mechanisms of release were deduced from the manner in which the release depended on the decay constant. It was established that the release of short-lived fission gases during irradiation was controlled mainly by pseudo-recoil, while chemical reaction between UC and water vapor, as well as knock-out, appeared to con-tribute much more significantly in the case of the longer-lived fission gases. The release of fission gas after reactor shutdown was shown to be governed by the UC-H₂O reaction. The ratio of the release due to this reaction in reference to the total release was found to be de-pendent not only on the concentration of the water vapor but also on the amount present of the accumulated reaction products. Also, a discussion is given on the inordinately high release of ^135mXe observed at 600°C.

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A fast neutron irradiation system was designed for performing activation analyses with fast neutrons on elements producing short-lived nuclides. The system consists of a Van de Graaff accelerator, a pneumatic transfer system, a γ-ray detection system and a control system. All the process steps of the activation analysis, such as irradiation, transfer of the sample and measurement of γ-rays are carried out in automatic sequence, governed by a programmed control system. The main part of this paper is devoted to a description of this control system. The apparatus was successfully tried for the analysis of ^207mPb (T_1/2=0.797 sec). The activity was identified with the apparatus set to measure half-life. Background can be reduced by select-ing the time sequence of analyzing processes.

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