Disposal of radioactive solids or solidified wastes in the ground is at present forbidden in Japan, mainly because of the difficulties in the evaluation of the migration of leaked radionuclides and of the radiation dose to which the public would be exposed by the disposed wastes. First of all, the behavior and the migration of radionuclides in the environment is quantitatively expressed. Then, the internal dose rate received by the public is estimated under suitable assumptions.
Ten radionuclides contained in radioactive wastes and three ecological paths of the nuclides in the environment are discussed (i.e. the paths through drinking water, sea foods qnd vegetables). It is concluded that the critical nuclides in this disposal scheme are ⁹⁰Sr and ^110mAg, and that the internal dose is mainly governed by the intake through vegetables. The safety of the ground disposal of radioactive wastes is also evaluated.

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In order to improve the performance of a commercially available charcoal filtel paper (Toyo Roshi, Type CP-20) and of a charcoal cartridge (Toyo Roshi, Type CHC-50) for collecting airborne radioiodine under high relative humidity, the charcoals were impregnated with triethylenediamine (TEDA), stannous iodide (SnI₂), potassium iodide (KI+I₂) or else with potassium thiocyanate (KSCN). The impregnated charcoals were examined for their dependence of collection efficiency on the properties of airborne iodine, on the sampling period and on the face velocity, and the results were compared with unimpregnated charcoal as reference. The airborne radioiodine used as samples was obtained from the exhaust ventilation systems at the ¹³¹I production plant, and from the fuel reprocessing test plant, both belonging to the Japan Atomic Energy Research Institute.
The charcoals impregnated with TEDA or SnI₂ were found to show greatly improved performance compared with the unimpregnated charcoals; the collection efficiency of the charcoal cartridge and of the charcoal filter paper was maintainted at levels above 85 and 80%, respectively, over a period of 14hr of sampling. It was found, however. that the collection performance was impaired by the presence of chemically reactive gases such as NO₂ and organic vapor. The charcoals impregnated with (KI+I₂) and with KSCN showed almost no improvement in their collection efficiencies.

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An air-cleaning system embodying activated charcoal filters was constructed for a large-scale ¹³¹I production facility at the Japan Atomic Energy Research Institute, for the purpose of removing ¹³¹I released continuously into the exhaust air stream from the production facility.
The system was continuously operated for about 47 months, and changes in the removal efficiency of the ¹³¹I filter for the exhaust air stream was observed during this period.
In one run of ¹³¹I production, the removal efficiency changed significantly, possibly due to a change in the chemical form of ¹³¹I released, accompanying the progress of the ¹³¹I production process.
When operated at the maximum air flow rate of the filter, it showed an efficiency greater than 90% on the average over a period of 20 months.

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A small reactor simulator was constructed, utilizing an analog computer and the console of JRR-1.
The simulator TRS (Tokai Reactor Simulator) is designed for reactor operation trainee experiment. With this simulator, experiments can be performed that aim at implanting a better understanding of the spatial dependency of the in-core neutron flux, including the case of critical approach and the measurement of neutron importance. The TRS is a wide-range kinetics simulator operative continuously from start up to full power.
The article first outlines the simulator and some examples of experiments performed therewith are described.

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This articles briefly summarizes five cases of inter-university cooperative arrangements for use of government nuclear facilities in Japan.
They can be classified into three categories as follows: (a) Cooperative use of nuclear facilities of non-university government laboratories, (b) Joint university research institute, (c) Cooperative use of university nuclear facilities.
One example of category (a) arrangement has been working effectively since 1961 for university research workers. The Japan Atomic Energy Research Institute accepted a request to let universities use several research reactors and other facilities.
The γ-field facility of the Ministry of Agriculture and Forestry also is now available for university research workers.
The unique example of category (b) is the Research Reactor Institute of Kyoto University. This institute was established in 1963 and it has a tank type research reactor (5MW), an electron linac and other experimental facilities. A multi-purpose critical assembly is now under construction and plans are being made for a high flux research reactor.
There are two examples of category (c) arrangement: the Fast Source Reactor of the University of Tokyo and the JMTR Radiation facility of the Tohoku University.
Problems faced commonly by many of the above mentioned cooperative arrangements include the following:
(1) Difficulties found by private and prefectual university research workers, and graduate students in joining these organizations.
(2) Difficulties in the evaluation of research results obtained by cooperative research groups and from the use of common facilities.
(3) Compatibility between the institute staff's own research program and that for utilization of the facilities for the cooperator.
(4) Inadequacy of funds and personel for the cooperative programs.

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