Norikatsu Ootsuka

Radiation Damage of Fluorocarbon by Krypton-85 Beta-Rays, (II): Radiolysis of Some Fluorocarbons by Cobalt-60 Gamma-Rays

Ampoule irradiations using 60Co γ-rays were undertaken on CC12F2, C2C14F2 and C2C13F3 to gain information concerning the radiation damage of fluorocarbon, used as solvent in the recovery of 85Kr from the off-gas of fuel reprocessing plants operating on the solvent absorption process. The dose rate was varied in the range of 2.6×104~8.0×105 rad/h and the irradiation temperature in the range of −100~70°C. Identified among the numerous degradation products were six compounds deriving from CC12F2, eleven from C2C14F2, and eleven also from C2C13F3. The decomposition yield of each of these fluorocarbons increased with irradiation temperature, and decreased with dose rate. It rose roughly in proportion to the absorbed dose. Comparison of decomposition behavior between the four fluorocarbons (including CC13F covered in the preceding report) was made in reference to the irradiation temperatures corresponding to those at which these fluorocarbons would respectively be applied in practice as solvent for 85Kr absorpt...

Release of dissolved 85Kr by standing.

The experiments on the release of dissolved 85Kr by standing at room temperature were carried out to examine the influence of liquid level in a sampler and properties of solvent on the release efficiency. Six kinds of organic solvents as well as water were taken as solvents.The half-life period in case of the decrease in concentration of the dissolved 85Kr which was used as an index of release efficiency, was proportional to the liquid level in the sampler and was inversely proportional to the diffusion coefficient of Kr gas in solvent. For organic solvents belonging to homologous series, the half-life period became longer with increasing the carbon number of solvent molecule. From the relationship between the half-life period and the carbon number, the release efficiency in the dissolved 85Kr can be predicted for any commonly used solvent as a practical application. This method was found to be an effective means of removing the dissolved 85Kr of low level though it takes rather long time.

Degassing of dissolved 85Kr by N2-stripping method.

The experiments on the degassing of dissolved 85Kr by the N2-stripping method were carried out to examine the influence of temperature and properties of solvent, as well as flow rate of N2 gas on the degassing efficiency.The half-life period in case of the decrease in concentration of the dissolved 85Kr which was used as an index of degassing efficiency, was proportional to the reciprocal of temperature and was inversely proportional to the flow rate of N2 gas. It became longer with increasing the viscosity of solvent. No influence on the degassing efficiency was observed to be exercised by the solubility of Kr gas in solvent and the surface tension of solvent. For organic solvents belonging to a homologous series, the half-life period became longer with increasing the carbon number, molecular weight and boiling point of solvent, respectively.

Dosimetry in Krypton-85 Gas Irradiation Vessel

Dose rates obtained in a cylindrical vessel filled with gaseous 85Kr source were measured using blue cellophane dosimeter. Besides obtaining the dose rate distribution within the vessel, the dose rate at vessel center was correlated to the 85Kr pressure, to the shape and size of the vessel, and to the material forming the inner wall surface. The 85Kr source used in the experiment amounted to 300 Ci (11.1 TBq), with a radioactive concentration of 35.9 mCi/ml NTP (1.33GBq/m/NTP). The dose rate in the vessel was found to rise in direct proportion to the 85Kr pressure, and also to increase in keeping with the size of the irradiation vessel and with the atomic number of the material lining the inner wall. Fairly good uniformity of the dose rate was noted, a ratio of only 1.33 being registered between the values obtained at the locations of maximum and minimum dose rate. The observed relationship between the dose rate and 85Kr pressure agreed fairly well with a theoretical expression derived for spherical β sou...

Radiation Damage of Fluorocarbon by Krypton-8 5 Beta-Rays, (IV) Irradiation Experiments using Krypton-85 Beta-Rays on Trichlorofluoromethane in Batch and Flow System

A series of two irradiation experiments at -30°C were performed on CCl3F using a 282 Ci 85Kr source, with the irradiation facility arranged in (a) and (b) in flow modes of operation, to determine the decomposition yields in relation to absorbed dose, and to observe differences in the CCl3F decomposition behavior according to combination of radiation source and operating mode. The experiments revealed—among other data—that: (1) The decomposition yield of CC l3F and the yields of the individual degradation products were related linearly to the absorbed dose, with coefficients representing CC13F energy decomposition of 0.026mol/o/Mrad (G=3.2) in batch and 0.053mol/o/Mrad (G= 6.7) in flow system; (2) No significant difference in the decomposition yield was observed between irradiation by 86Kr β-rays and 69Co β-rays; (3) Compared with batch, flow operation was found to provide higher CCl3F decomposition yield; (4) Inspection of the inner surfaces of the circuit upon disassembly of the facility after the experi...

Dose measurement of 90Sr source for radiation chemical reaction.

The irradiation characteristics for a plate source of 90 Sr 222GBq (6 Ci) were examined with the blue cellophane dosimeter and the thermoluminescence dosimeter. The 90Sr source used has the active area of 35x20mm2 and the surface concentration of 31.5 GBq (0.85 Ci)/cm2. The high dose rate of 1.1 kGy (1.1x10(5) rad)/h was obtained at the distance of 5 cm from this source. At that time, the isodose curve determined by the blue cellophane was similar to a circle. The peak in depth dose curve was fairly displaced to the shallow direction in comparison with that obtained from the irradiation with an electron beam accelerator (2 MeV). The calculated dose rate attains to 800 kGy (i.0x10(7) rad)/h at the distance of 5 cm from the source when the infinite plate source with the maximum surface concentration (1.51 TBq(40.7Ci)/cm2) is placed on a plane.