The synthesis technique using the deterministic optimal linear regulator with quadratic performance index is applied to a simplified nonlinear dynamics model of boiling water reactor with forced recirculation. The controller is first formulated on the basis of the currently used technique of the linear regulator applied to a linearized model of the plant ; it is then modified by adding appropriate integration-type actions by trial-and-error to improve the controller performance.
The result of computer simulation suggests that, with simple modifications such as the addition of integration actions and the use of variable gain and reference, the linear regulator technique may be applied successfully to the control of a nuclear power plant for a change in power output without resorting to more sophisticated techniques.

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The downward progress of the advancing front of a liquid film streaming down a heated vertical surface, as it would occur in emergency core cooling, is much slower than in the case of ordinary streaming down along a heated surface already wetted with the liquid. A two-dimensional heat conduction model is developed for evaluating this velocity of the liquid front, which takes account of the heat removal by ordinary flow boiling mechanism.
In the analysis, the maximum heat flux and the calefaction temperature are taken up as parameters in addition to the initial dry heated wall temperature, the flow rate and the velocity of downward progress of the liquid front. The temperature profile is calculated for various combinations of these parameters. Two criteria are proposed for choosing the most suitable combination of the parameters. One is to reject solutions that represent an oscillating wall temperature distribution, and the second criterion requires that the length of the zone of violent boiling immediately following the liquid front should not be longer than about 1 mm, this value being determined from comparisons made between experiment and calculation.
Application of the above two criteria resulted in reasonable values obtained for the calefaction temperature and the maximum heat flux, and the velocity of the liquid front derived therefrom showed good agreement with experiment.

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A method of synthetic kernel approximation is examined in some detail with a view to simplifying the treatment of the elastic moderation of fast neutrons. A sequence of unified kernel {f_N} is introduced, which is then divided into two subsequences {W_n} and {G_n} according to whether N is odd (W_n=f_2n-1, n=1, 2, …) or even (G_n=f_2n, n=0, 1…). The W₁ and G₁ kernels correspond to the usual Wigner and GG kernels, respectively, and the W_n and G_n kernels for _n ?? 2 represent generalizations thereof. It is shown that the W_n kernel solution with a relatively small n( ?? 2) is superior on the whole to the G_n kernel solution for the same index n, while both converge to the exact values with increasing n. To evaluate the collision density numerically and rapidly, a simple recurrence formula is derived. In the asymptotic region (except near resonances), this recurrence formula allows calculation with a relatively coarse mesh width whenever h_a ?? 0.05 at least. For calculations in the transient lethargy region, a mesh width of order ε/10 is small enough to evaluate the approximate collision density ψ_N with an accuracy comparable to that obtained analytically. It is shown that, with the present method, an order of approximation of about n=7 should yield a practically correct solution diviating not more than 1% in collision density.

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Krypton-85 is a radioactive noble gas with a long half-life, and its release to the environment results in global contamination. The concentration of ⁸⁵Kr in the atmosphere is gradually increasing today, and it will reach the order of 10⁴ pCi/m³ by the year 2000 if this nuclide is continued to be released without removal. The release will likely be restricted in the future under international control, though the dose rates due to ⁸⁵Kr absorption based on the ICRP recommendation is at present being reevaluated on account of its appearing to be excessively high.
In this paper, the removal rates required for ⁸⁵Kr are estimated to cover several decades, using the linear programming method, with a selection of given constraints specifying different criteria for limiting atmospheric pollution, and based on an assumed program for nuclear electricity power generation and construction of reprocessing plants.
Some parameters contained in the objective function are difficult to fix, particularly the equipment and operating costs and the penalty for absorbed dose rate, but some results are given as indication, with these parameters tentatively assumed. As an example, adopting the constraint to limit to 10⁸ Ci the accumulation in atmosphere of ⁸⁵Kr released from reprocessing plants in Japan should require the removal of 80...90% of effluent ⁸⁵Kr at the reprocessing plants by the year 1990 at the latest.

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Annealing experiments were carried out on irradiated UO₂ in argon gas under high pressure (600 and 1, 000 kg/cm²) as well as atmospheric, at temperatures of 1, 400°1, 600°. The effects of high external pressure on the behavior of fission gas bubbles in the irradiated UO₂ were studied by comparing replica electron micrographs of fractured surfaces of specimens annealed under different temperatures and pressures. The results indicate that high pressures such as above 600 kg/cm² can be effective in surpressing the growth of fission gas bubbles in both intergranular and intragranular zones, and in inhibiting the joining together of intergranular bubbles to form direct passages for fission gas release.

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