A laboratory air sampler, that has high mobility and reduced operational noise, has been developed. It is used to collect the air-borne particles in such areas that are out of daily watching by stationary monitors or contaminatated accidentally by radioactivity. Primary considerations in the design of the instrument are (1) to reduce external size and weight, (2) to deduce operational noise. Noise level is less than 53-59 phones at a distance of one meter away from the instrument. Various filter paper and active carbon cartridge filter for the filteration of iodine can be installed in a filter box at the top of the instrument and easily replaced.
A few methods for neutron dose measurement have been examined. In this paper, a simple method for dose calibration by a low power reactor is introduced. Calibration with the theoretically calculated values of some neutron dosimeters was made. This calibration was based upon the neutron flux values estimated by the activation method using the neutron field of UTR-B operating at 0.1W. On The calibration with the Bendix fast neutron dosimeter and thermal neutron dosimeters, the experimental values were found to be close enough to the theoritical values to be of practical use from the operational health physics stand point.
The disposal of radioactive waste materials resulting from the operation of nuclear power reactor is a very important problem in the design and operation of nuclear power plant. This report reviews the control or regulation of liquid radioactive waste and the experimental results of the JPDR for the past three years. Origin of the radioactive waste is mainly treated water in regeneration of radioactive resin and cooling water of incore monitor. Based on the experimental results of 1000hr continuous operation, the daily liquid waste discharged was about 26m3 in volume and 900μCi in activities. These radioactive liquid wastes are treated by filteration and demineralized or storaged in the decay tank in some cases. Lastly it was measured by sampling methods. If liquid waste had less than 10-4μCi/ml, it was discharged to the discharge canal which leads to ocean. This canal carries, at the same time, the cooling water of turbin condenser, about 6000m3/hr, which dilutes the concentration of liquid waste about 3000 in factor. Then, the concentration of radioactive isotopes in the liquid wastes leaving plant site was well below the MPC limits for unrestricted areas as established by the ICRP and Japanese Government authorities.
Reduction of radiation injury and evaluation of risks following exposure are both of great importance in the peaceful use of nuclear energy. In this paper discussions are given to the latter and relevant problems are listed as to the former. For the practical purpose of radiation protection against radiation hazards it often becomes neccessary to establish levels as to the expected exposure dose, for which not only scientific but also social and economical considerations have to be taken into account. There are three categories of effect to be considered in biological evaluation: 1, early effect due to acute exposure, 2, late effect and 3, genetic effect in the population at large. Evaluation of risks requires a quantitative information about dose-effect relationship, as to which two contrastic hypotheses are available, i. e., the one which assumes a linearity and the other which proposes a threshhold dose. Present state of knowledge, in which no mechanisms of biological effect of radiation are erucidated, has to acknowledge both hypotheses to be practical and useful approach, each being complementary to another. Dose-effect relationship with regard to late effect, which is of vital importance in man, is discussed from currently available data. Several research themes which may contribute to the biological evaluation of risks are illustrated.
On the basis of results of recent experiments carried out by the members of the National Institute of Radiological Sciences, some of recent problems on recovery from radiation injuries in biologically important molecules, cells and whole organisms are briefly reviewed. At molecular level, nature of enzyms which are responsible for repair from DNA damage in microorganisms is investigated by the workers of the laboratories of Dr. K. Suzuki and Dr. S. Nakai. In order to analyze mechanism of chromosome break and reunion, fine structure of chromosomes is studied by Dr. Y. H. Nakanishi. Using synchronous cell culture system, Dr. Terasima has examined in detail effects of fractionation of radiation dose on survival of cells, and has quantitatively demonstrated recovery from sublethal damage by irradiation under various conditions. Drs. Nakamura, M. Seki, S. Ichii, T. Yamaguchi, T. Tsuchiya, K. Hirashima and their collaborators are studying recovery processes in hematopoietic tissue of animals in relation to endocrine system, immunological responses and bone marrow transplantation etc. by their own methods. Pharmaceutical research is worked out by Drs. T. Hino and M. Shinoda. Cell population kinetics in the critical organs during recovery period from radiation damage at different temperatures are studied out with poikilothermic vertebrates by Drs. H. Etoh, Y. H. Taguchi and N. Egami. From these results, importance of consideration of recovery factors in estimation of risks from radiation is pointed out as conclusion.
In a recent decade, human cytogenetics has been developed very rapidly with advancement of tissue culture technique. This review introduces the basic mechanism of chromosome aberrations in human somatic cells, especially, leucocytes and relationship between abnormalities and irradiation. However, our knowledge about relationship between dose of radiation and quantity of chromosome aberration is not enough to clearly explain. Also it is the problem which will be studied in near future to clarify the causation of leucemia and other disorders.