An islandwide network for environmental radioactivity monitoring established in the Taiwan Province of the Republic of China in 1974 to provide radiation base line data for the government agencies, was described with reference to types of environmental samples taken and types of radioactivity monitored. Both gammaray spectroscopy and radiochemical methods were used to detect fission products and naturally occurring radionuclides in all environmental samples. Emphasis was placed on the analysis of long-lived fission products such as 90Sr and 137Cs. A special feature of the monitoring network is to analyze the fission products in diet of children which is a special nutritious lunch program for the primary school children. Relatively high activity from nuclear testing at Lop Nor during 1974-1978 is indicated with corresponding dates and sequence number of tests.
Being able to be determined by subtracting the gamma-ray ionization intensity from that obtained with ionization chamber, cosmic-ray ionization intensity in free air was estimated by using with 15l air-filled ionization chamber and 3″φ spherical NaI (Tl) scintillation spectrometer. Optimum applied voltage to 15l air-filled ionization chamber was determined in accordance with Scott and Greening's formula to obtain the ionization intensity caused by gamma-rays and cosmic-rays. Pulse-height distribution of cosmic-rays created in 3″φ spherical NaI (Tl) scintillation spectrometer was investigated for the precise determination of gamma-ray ionization intensity. Field measurements were carried out by using with these two instruments at about 1.5 meter above the ground in the several locations around Research Reactor Institute of Kyoto University. Cosmic-ray ionization intensity in free air was estimated from the results obtained with air-filled ionization chamber and was 3.33±0.15μR/hr equivalent in natural environment near Research Reactor Institute of Kyoto University.
An autoradiographic technique in estimating size of air-borne plutonium was studied by using ZnS(Ag) intensifier screen and Polaroid film. Effects of screen thickness, a weight percent of binder added and a particle size of ZnS(Ag) powder on a spot size of autoradiograph were examined. A calibration curve between alfa activity and spot size of autoradiograph produced under optimum exposure condition is presented. All procedures of the autoradiography can be performed without darkroom by the use of an improved Polaroid camera which has a double light-tight attachment.
During the test operations of JPDR-II (BWR), cracks were detected at primary pipe nozzle, and the inspections were made over about 2.5 years. In this report, the procedures such as shielding and removal of fuels which were taken to reduce radiation exposure during the inspections are summarized and the cost-benefit analysis of the shieldings were attempted to determine whether the optimum shieldings were made or not. The radiation doses was measured to be about 62 man·rem for 420 workers and the maximum individual dose was 1.3rem. The average cost to reduce exposures at various working areas was calculated approximately 1.4×105yen/man-rem. Especially, the provisional shielding at under core area reduced 61 man-rem and its reduction cost was 8.9×106 yen. Assuming that the economic and social detriment cost is 1, 000$/man-rem, it seems that the optimum shielding were taken, although the optimum conditions shifted depending on the economic and social detriment cost which cannot be simply determined. It was found that the optimum conditions depended on the order of combination of the provisional shields.
USEPA has conducted a series of surveys of disused U. S. radioactive waste sites at the Atlantic and Pacific Ocean. The author joined the surveys in 1976 and 1978. A characteristic method of the survey was the use of submersibles to collect samples of sediment, biota etc. and to recover radioactive waste packages at deepsea bottoms. Cement-solidified radioactive wastes packaged in drums were recovered during the surveys in 1976 at depth of 2, 800m in the Atlantic Ocean, in 1977 at 900m in the Pacific Ocean and in 1978 at 3, 800m in the Atlantic Ocean, respectively. The recovered packages have been investigated at Brookhaven National Laboratory. An 80 gallon package disposed of in 1960 and recovered in 1976 contained a cylindrical container (99×16.5cm∅) made of steel in the center of the package. Three pieces of fiber filters were enclosed in the steel container and a cement-liquid waste composite including 162μCi of 137Cs was found to surround it. It was estimated that the amount corresponding to the cumulative leach ratio ca. 56% was released during its stay on seabed for 16 years. It was found that ca. 1/3 of the drum was buried in the sediment. As a result of the investigation average corrosion rate of steel plate of the drum was 0.030±0.006mm/year for the sea water side and 0.046±0.006mm/year for the sediment side, respectively.