The concentrations of several radionuclides released from the stack of the research reactor, Kyoto University (KUR) were examined according to the modified procedure of the regulatory guidance “The measurement of released radioactive substances from a light water moderated power reactor.” It was found that the concentrations of all radionuclides detected such as tritium, iodine-131, -133 and strontium-90 etc. were sufficiently lower than the lower limit concentration in the air presented in the guidance except for the Ar-41. Then the radiation control system was established so that the average Ar-41 gas concentration for three months in the reactor room would not exceed the permissible concentration 4×10-7μCi/cm3 regulated by the law, setting the reasonable alarm level 5×10-6μCi/cm3 which is connected with the operational interval of KUR and the average Ar-41 concentration of the past twelve weeks.
It was demonstrated that DTPA (diethylenetriaminepentaacetic acid) enhanced the vascular permeability by the intradermal injection test in rats. This change was inhibited by the pretreatment of Epinephrine (vasoconstrictor). The enhancement of vascular permeability was also observed in the small intestinal tract when DTPA was injected intravenously and introduced into the gastro-intestinal tract of rats. As a result, it was considered that the enhancement of vascular permeability could induce side effects such as the decrease of blood pressure, vasodilation, hemorrhage or congestion in various organs after DTPA administration. Therefore, it was suggested that DTPA should be cautiously treated to humans.
Decontamination properties of radioactive liquid waste treatment facilities were studied from the data of radioactive concentration measured before and after the treatment. Evaporation treatment showed an excellent decontamination property, and every radioactivity of total α, total βγ and five important nuclides was not detected after this treatment. By chemical coagulation, total ã radioactivity was effectively removed, but total βγ radioactivity was not. The DFs for total βγ radioactivity distributed between one and ten according to the nuclides contained in liquid waste. DF values of about ten were obtained for 60Co, 65Zn and 54Mn, and 137Cs was almost not removed. The removal of 51Cr lay between these two cases. The treatment using organic ion exchange resin (Na+ form) removed every nuclides except 137Cs, but was not sufficiently effective for 137Cs. When 137Cs exists in liquid waste, it is necessary to use a vermiculite column after the treatment of chemical coagulation and/or ion exchange.
There is growing demand for shortend etching time of CR-39 plastics for practical use in individual neutron dosimetry. Generally, etching at high temperature makes this possible, though it has a tendency to roughen the detector surface. In this study the etch-pit diameter and surface were examined using CR-39 plates irradiated with alpha-particles and etched with aqueous solutions of 15 or 30wt% KOH or NaOH at 60-90°C for 0.4-20hr. It has been observed that etching time can be reduced to less than one tenth as a result of a rise from 60°C to 90°C without enhancement in surface roughness. Taking 30wt% KOH, 90°C as the optimum etching conditions, the diameter changes at the rate of 9.8%/°C in temperature, 7.6%/wt% in concentration and -1.0%/day in the time after preparation of etchant.
The external exposure to gamma rays from a radioactive cloud, i. e. the cloudshine, is an important exposure pathway. A computer code, AIRGAMMA, was developed to calculate quickly the cloudshine doses by interpolating normalized doses provided on the basis of the Gaussian plume model. The normalized dose is defined as the dose on the ground when a gamma-emitting nuclide is released at a rate of 1Ci/hr or the amount of 1Ci and the wind speed is 1m/sec. The code approximately takes account of depletion of the dispersing materials for calculation of the cloudshine doses, but ignores effects of the building wake and the mixing layer on the cloudshine doses. The interpolation of the normalized dose would not cause errors larger than 1% for most of the cases. The time for calculation of a dose is less than 2 msec on the computer FACOM-M380. The applicability of the approximations mentioned above is discussed in this report.
The diameter of mouth of etched nuclear track has generally been measured for the purposes of examining the properties of the incident particle, obtaining the registration characteristics of the track detector and also checking the qualities of both the etching procedures and the detector itself. For increasing the efficiency of the diameter measurement, the application of an automated TV device manufactured for image analyzation was examined for the etch pits of α-particles on CR-39 plastic track detector; a comparison with precise microphotographic method was carried out. It has been confirmed that the mean value of the diameters could be determined with a sufficient accuracy and reproducibility, if the threshold level of the darkness for the etch pit image was appropriately set. It should be noted, however, that the standard deviation of the distribution of etch pit diameters was overestimated by the magnification of 1.3-1.4, which was attributed to the fluctuation of the measured values from position to position in a single visual field.
The literature on conversion of tritium gas to tritiated water in various environments is reviewed. The conversion mechanisms and the conversion rates are as follows. 1. In the oxidation with oxygen and the isotopic exchange with water, tritium β-rays and metal catalyst are effective. The oxidation rate is -0.02%/day at initial tritium concentration ≤10-2Ci/l and -2%/day at 1Ci/l. In the presence of oxygen and water, it is not clear whether the exchange reaction occurs or not because of the small amount of data. 2. For biological conversion, soil microorganisms contribute significantly. The conversion rate is greater than 10%/hr. The tritium gas deposition velocity, which includes the uptake rate of tritium gas by soil and the conversion. rate, ranges from 0.0025 to 0.11cm/sec and is influenced by temperature and moisture of the soil. 3. Tritium gas is converted to the tritiated water througn the reaction with hydroxyl radical produced by sunlight in the atmosphere.