This paper deals with a new search technique for optimum using a fuzzy automaton, which has been developed for the purpose of determining a desirable rod pattern for smoothing the core power distribution. Using the algorithm thus developed, the optimal input vector applied to a controlled system whose characteristics are unknown is determined automatically from a learning operation of the fuzzy automaton when an initial guess and a hypothetical range of optimal input vector are given. The characteristics of this algorithm are examined for an example of its application to a simple problem. The optimal control rod pattern for smoothing the core power distribution is also determined by this algorithm in a simulation study using the three-dimensional boiling water reactor simulator "FLARE". It is concluded that optimum points are obtained with sufficient convergence and with only a small increase in the number of iterations and computation time accompanying an increase in the number of components of the input vector. The predicted optimal control rod pattern in the simulation study can be considered reliable.

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There occurred in 1971 an accidental exposure to γ-rays from an ¹⁹²Ir source received by persons not regularly occupied in radiation work. To serve in planning the therapeutical treatment, a method for estimating the γ-ray exposure received by these persons was devised.
The method is based on the idea of using bearing jewels collected from the patients' wrist watches as monitor sample for tests on their thermoluminescence. Applying this method, it was estimated that the exposure sustained by the three patients in question was 761, 77 and 40 R. The method thus developed should prove useful for estimating the exposure sustained by patients involved in a radiation accident.

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The synthesis method is combined with the first-flight collision probability method to treat the nonuniformity of the medium along the axial direction. The neutron flux in a three-dimensional system is expressed by the product of a known trial function in the horizontal plane and an unknown function along the z-axis. The trial function in the x-y plane is evaluated in terms of the first-flight collision probability calculated in either one or two-dimensional system. And the unknowns are determined in each axial subzone by solving simultaneous equations with use made of the first-flight collision probability in a system reduced to one dimension by adopting a homogenized cross section. As an example we calculate the flux distribution in the axial direction in a finite lattice cell composed of a moderator and a fuel rod with two different compositions in the upper and lower axial zones.

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Celluloid film, used as for α-track detection for its being one of the most sensitive solid state track detectors, was irradiated up to 3.5×10⁷ rad by ⁶⁰Co γ-rays. The radiation damage was examined by weighing a piece of the film before and after etching with sodium hydroxide solution under various conditions. Six molar sodium hydroxide solution at 50°C was found to be the most suitable etching solution for this irradiated celluloid film. On measuring the optical density, it was seen that the absorption curve for UV light shifted to the longer wavelength side accompanying an increase of absorption dose of γ-ray energy on the film. Both the gravimetric and the optical methods of determining radiation damage indicated its dependence on the γ-ray absorption dose. The sensitivity of α-track registration was also estimated by examining the appearance of α-track under the optical microscope according to etching time. The critical energy of the celluloid film for the registration of α-tracks decreased with the absorption dose of γ-rays.

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In this paper, the frictional pressure drop in an isothermal liquid metal-gas two-phase flow through a rectangular channel with large width-to-height ratio is treated semiempirically for a NaK-N₂ two-phase flow system.
The frictional pressure drop in the two-phase flow is compared with the following two reference values:
(1) The frictional pressure drop in the liquid flowing alone in single phase with the same velocity as that of the liquid in the two-phase mixture.
(2) The frictional pressure drop in the liquid flowing alone in single phase with the same mass flow rate as that of the liquid in the two-phase mixture.
The comparison with the former reference value is necessary for the prediction of friction loss in a liquid metal MHD generator channel whose medium would be two-phase mixture.
The semiempirical analysis was performed assuming the two-phase mixture to be a continuous medium with its properties, e. g. viscosity and density, defined by void fraction and the velocity determined by the total mass flow rate.
In the region of low slip and density ratio ρ_g/ρ_l, the frictional pressure drop in the two-phase flow appeared to be smaller than that due to the liquid flowing alone with the same velocity as that of the liquid in the two-phase flow.
The experiments have been undertaken with the NaK-N₂ two-phase mixture flowing through a rectangular channel (4×60mm²).
Data were taken over the following parameter range:
NaK velocity: 5∼30m/sec, Void fraction: 0∼70%
Density ratio: 0.006∼0.013, Quality: 0.07∼1.10%.

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The reactor noise analysis technique is particularly useful in reactor diagnosis for on-line monitoring if the raw noise signals can be processed in almost real time.
An on-line reactor noise analysis system has been developed with use made of the mini-computer HITAC-10. This system utilizes functions for calculating the power spectral density in almost real time, plots the output by digital incremental plotter, and displays the results by means of color graphic display equipment, in order to detect anomalous reactor conditions with the statistical technique.
Using this system, reactor noise signals have been measured and analyzed under various operational conditions in the JMTR. The variance of the power spectral density is found to fit a logarithmic probability density function. This function is independent of the frequency, but is dependent on the number of sampling functions.
A logical procedure for anomaly detection based on statistical characteristics has been developed. It is applied to a case where it is supposed that the PWR operating mode in the OWL-1 is the normal process and that the BWR mode is the anomalous. It is demonstrated as a result, that this procedure can successfully detect anomalous processes.

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The γ-radiolysis of water subjected to gas bubbling has been studied using a specially desinged gasloop. During the irradiation, N₂ gas was bubbled from the bottom of the irradiation vessel. As the N₂ gas feed rate was raised, the apparent G(H₂) valve increased in keeping therewith, from 5×10^-3 to 0.26. However in the presence of a sufficient amount of O₂ or H₂O₂, G(H₂) was raised almost to the level of the molecular yield. With reasonable assumptions, it could be concluded that 3∼5×10^-6mol/l of H₂O₂ was sufficient to reduce the back reaction of molecular products to less than 10% under the present experimental conditions. It was also found that the G(H₂) value increased with CH₃OH concentration roughly in proportion to log(CH₃OH), and reached 3.1 with 0.1mol/l CH₃OH.

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In order to study the release process of fission xenon produced by decay of the precursor iodine in natural graphite powder, post-irradiation experiments were carried out at 1, 000°C soon after 20min irradiation with UO₂ powder. In an experiment with interruption (2hr heating-10 day cooling-10hr heating), it was found that the decay of ¹³³I to ¹³³Xe caused a fraction of the ¹³³Xe produced to be released rapidly, while the remaining fraction was released gradually. This was followed by a continuous heating experiment, during which the release rates of ¹³³Xe, ¹³⁵Xe and ¹³⁵mXe were measured, and in which production and release of xenon occurred simultaneously in a manner similar to conditions prevailing under actual irradiation experiments. The rates of nuclide release were explained by assuming the same release probability for each xenon nuclide as that for ¹³³Xe in the first experiment. The origin of the initial rapid release by decay of iodine to xenon was considered mainly to be the change of chemical interaction between the defects and the atoms trapped therein. The release behavior of xenon after its production was explained by assuming that the activation energies for the release from the defects were lowered by about 10kcal/mol by the decay.

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