A new approximate method for calculating the effectiveness of multiple control rods fully inserted in a reactor is described. This method is appicable to a bundle of many control rods, regardless of the number of rods, as well as to an array of a limited number of few rods.
Using either the sink model or the well model, a reactor equation of kernel form is obtained.The reactor equation is a two-dimensional diffusion equation with two-group diffusion kernel. In order to facilitate numerical computation of the eigenvalue, the integral equation is reduced to a set of linear homogeneous equations, by dividing the reactor into a large number of unit cells containing at most one control rod.
This method has been programmed for the IBM 7090, the code being given the designation ELC. The iterative procedure used converges much faster than the standard accelerated finite-difference programs. Using the ELC code, the effectiveness of an array of four control rods fully inserted in a cylindrical reactor was calculated. The results are in good agreement with those found by the Scaletter-Nordheim method. In the case of a large number of control rods, there is no alternative method to be compared with.

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Time optimal control of nuclear reactors has been studied using Pontryagin's maximum principle. Since the results are intended for application in a digital computer control system, restrictions on the maximum reactivity and on the maximum over (under)-shoot of reactor power are imposed to derive a practical control pattern. A study of continuous time systems is attempted in this paper with the view to deriving the basic characteristics of optimal solution and providing useful guides to future work on discrete time systems, including digital computer, to be treated in a forthcoming paper.
To facilitate synthesis of optimal control, the reactor model is simplified with the use of a one group model for delayed neutron and prompt jump approximations. As a result, the time optimal control pattern is found to be uniquely determined in a delayed neutron density (or reactor power) vs. reactivity phase plane for any range of power variation. The optimal control law is simple, and can be adopted in a feedback control system.

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As a method of rapid separation, high voltage electrophoresis(H.V.E.) was applied to analyze various ionic species of Ru(III) and Ru(IV) present in solutions. Change of the ionic forms in solution after preparation, and as well as their ultimate equilibrium state, were investigated in chloride media. In a similar manner, the effect of complexing agents, i.e. lactic acid, oxalic acid and nitrilotriacetic acid, on the ionic forms of Ru(III) and Ru(IV) were surveyed. The results obtained were as follows.
(1) Various ionic species of ruthenium coexisting in a dilute hydrochloric acid solution separated into four or five zones of migration in the case of Ru(III) and six or seven zones in the case of Ru(IV), after periods depending on their mobility.
(2) Using an equilibrated sample, it was found that the ionic species practically did not change during a separation time of 5 to 18 min. Consequently, one can follow the kinetic changes of the ionic species if the reaction rate is not too high for neglecting reactions occurring during the elapse of a few minutes.
(3) From differences in ratio between the relative amounts of several migrated ionic species according to Cl- or OH- concentration, it was attempted to estimate the composition of Ru(IV) chlorocomplexes.
(4) In crimplexing media, the ionic forms involving Ru(III) did not change, while those of Ru(IV) clearly changed due to the formation of complexes. This behavior indicated a difference between Ru(III) and Ru(IV) in the grades of complex formation.

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Determination of strong complexing species contained degradation products formed by the reaction of nitric acid on kerosene diluent was performed through: (1) observation of change in the absor-bancy of nitroparaffines (at 1563 cm^-1), of carboxylic acids (at 1694 cm^-1) and of nitrate esters (at 1640 cm-1) against γ-activity of ⁹⁵Zr-⁹⁵Nb extracted into the degraded kerosenes; (2) separation of the main complexing species from the degraded kerosene by an acid-alkali treatment; and (3) nitration of oleic acid with nitrogen oxide gases and observation of change in its extractability for ⁹⁵Zr-⁹⁵Nb. It was conclusively established that nitroparaffines were among the main complexing species, and exhibited a strong retaining power on fission products, especially ⁹⁵Zr-⁹⁵Nb. Some possible retention mechanisms for fission products are proposed and discussed on the basis of tautomeric equilibria of nitroparaffines.

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For use as uranium tracer, ²³²U was prepared by neutron irradiation of ²³¹Pa in JRR-2. Carrierfree ²³²U produced in the target material was separated by solvent extraction with TIOA in an HCl-HF system, and purified by the anion exchange method using Dowex 1×8. The radiochemical purity of ²³²U was examined by means of alpha and gamma spectrometry, and it was confirmed that the ²³²U. obtained by this method was of sufficiently pure quality as uranium tracer to be used in very low level determination of uranium isotopes in natural samples. Furthermore, with the view to efficient production and radiochemical purification of ²³²U, the relative quantities of various by-product nuclides were estimated.

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