Yoshihide Komaki

Growth of fine holes by the chemical etching of fission tracks in polyvinylidene fluoride

Abstract Growth of holes in polyvinylidene fluoride film exposed to fission fragments in oxygen and etched in sodium hydroxide solutions was followed by measuring gas flow through the film as well as by electron microscopy. The radial etching rate was exceedingly small and it took more than a few tens of hours to obtain holes several hundred A in diameter. Electron micrographs showed the track width to be fairly constant along its length, this being consistent with quite a large ratio (the etching rate along the track)/(the redial etching rate) deduced from gas-flow data. Etched tracks viewed by an electron microscope showed a curvature. The reason for the appearance of the curvature is not clear. The chemical etching in potassium hydroxide solutions was also studied. The etching proceeded much faster than in sodium hydroxide solutions. But at high concentrations, the deposition of crystallites occurred and the etching rate decreased with increasing concentration.

Radicals in heavy ion-irradiated polyvinylidene fluoride

Abstract Heavy-ion irradiation-induced radicals in polyvinylidene fluoride films were examined using electron spin resonance (ESR) spectrometry. The films were bombarded by 79 Br 12+ (160 MeV), 35 Cl 9+ (150 MeV), 35 Cl 6+ (70 MeV) and 12 C 6+ (90 MeV) ions from a Tandem accelerator at 5.7 K and then measured at 77 K using ESR. Changes in the ESR spectrum produced by ion irradiation closely resembled that of γ-ray irradiation. With an increase in the ion fluence, the polyenyl-type radical predominates. The radicals reacted with O 2 to yield a peroxy radical when exposed to air at room temperature. The presence of oxygen-induced species was related to the etchability of the heavy ion latent track.

Growth of fine holes in polyethyleneterephthalate film irradiated by fission fragments

Growth of fine holes by chemical etching in polyethyleneterephthalate films exposed to fission fragments were followed by measuring gas flow through films. The etching rate along tracks and the radial etching rate were determined at hole diameters of 100–3000 A and hole densities of 106–108/cm2.

Scanning electron microscopy of nuclear pore filters in poly(ethylene terephthalate) and ethylene-tetrafluoroethylene copolymer

Abstract The interior of nuclear pore filters was observed by high resolution scanning electron microscopy. In poly(ethylene terephthalate) the interior of the hole with nodules of some widths was observed and the tapering angle observed from the cross section of the hole agreed with that calculated from the ratio of etching rates. In ethylene-tetrafluoroethylene copolymer the holes lie among the fibrils. Only ∼40% fission fragments penetrated and the residual remained in the 12 μm thick film from the observation of cross section of holes and from measurement of radioactive distribution of incident nuclides in the film. In either film the irregular surface was assumed to be induced by the difference of etching between the amorphous and the crystalline regions.

Thermochemical and experimental considerations of NOx composition and iodine species in the dissolution of spent PWR-fuel specimens

Abstract The NOx composition and iodine species in the dissolution of spent fuels are discussed on the basis of thermochemical calculations and experimental results. The influence of N0x sparging on the expulsion of iodine is also discussed. The dissolution of a spent PWR-fuel specimen (–3g) in 30 ml of 3.5MHNO3 at 100°C is calculated to yield a concentration of 7×10−2atm of N02, which is 80% of the total NOX in the dissolver. This N02 fraction is much higher than experimental values of 15% or less that were reported for dissolver off-gas cooled near to room temperature. The high N02 fraction suppresses the formation of iodate (IO3 −) in the dissolution. The calculations predict that IO3 −) is not formed in 3.5 M HNO3 at 100°C at an NO2 pressure ≥3×10−2 atm (3kPa). Attempts to expel iodine from the fuel solution indicated that the main iodine species in the solution was colloidal iodine and not iodate (I03 −) which earlier workers postulated. The obtained experimental results are consistent with the therm...

The effect of coexistent gases during fission fragment irradiation on track etching in polyvinylidene fluoride film

Abstract We have studied the fabrication of a porous-membrane filter made from polyvinylidene fluoride film which was irradiated by fission fragments and etched chemically. Then, the effect of coexistent gases during fission fragment irradiation was examined. There has been no previous reference to the use of fluoropolymers as nuclear track detectors for examining the effect of coexistent gas during irradiation for the track emergence. It was found that the etching rates of tracks increased with O 2 and NO, decreased with NH 3 and SO 2 , and were unchanged with N 2 , in comparison with those in vacuum. The hole diameters were determined by measurement of gas flow rate through the holes. It was inferred that with O 2 and NO, some oxygenated species were formed, in vacuum and with NH 3 the crosslinkings proceeded, especially with NH 3 , and with SO 2 the acidic products adsorbed into the tracks neutralized the alkali solution. The effect on the track etching rate corresponds also to the shapes of each etched track in the micrographs.

Interaction of Iodine with an Extractant of 30% TBP/70% n-Dodecane

The interaction of iodine species with “To-irradiated extractants of 30% TBP/70% n-dodecane was examined to infer the behavior of iodine downstream of the dissolution step in reprocessing. When a simulated spent-fuel solution (in which the main iodine species was colloidal iodine) was contacted with the extractant with irradiation dose of 2.8x102C/kg or less at 25°C, 70 to 80% of iodine was transferred to the organic phase together with 100% of uranium. About 50% of the iodine was retained therein during back-extraction of uranium by water at 60°C and transferred to aqueous phase in the solvent cleaning by alkaline solution. Only 4 to 5% of iodine was finally fixed in the organic phase. When the extractant was irradiated to 103C/kg or more, a “third phase” appeared in extraction step and the majority of iodine (about 65%) was sorbed in this phase. Over 90% of elemental iodine (I2) in a UO2(NO3)2-HNO3 solution was extracted to the organic phase regardless of irradiation dose of the extractant and half of i...

Heavy ion track registration in polyvinylidene fluoride

Abstract The paper presents some results on the tracks of heavy ions registered in polyvinylidene fluoride film. Polyvinylidene fluoride has a registration sensitivity to reveal the tracks for ions heavier than the Cl ion after etching. The estimated threshold value for the track registration was more than 12–13 MeV amu -1 . Clear-cut etched holes were obtained for the films perpendicularly irradiated by 150 MeV 58 Ni 10+ and 115 In 10+ ions. This films also seems to be promising as a nuclear track microfilter.

Influence of NOx and HNO2 on iodine quantity in spent-fuel solutions

The quantity of iodine in spent-fuel solutions tends to decrease with an increase in the dissolution rate. This phenomenon is ascribed to the presence of nitrous acid (HNO 2 ) generated in the dissolution process because of the following three findings: (a) in a hot nitric acid solution, the steady-state HNO 2 concentration increases with an increase in the rate of its production and decreases with an increase in temperature, (b) the HNO 2 decreases the quantity of colloidal iodine (the main component of residual iodine in a simulated spent-fuel solution) in proportion to its concentration up to ∼3.0 x 10 -3 M, and (c) a higher dissolution rate of UO 2 causes a higher HNO 2 production rate, hence, a higher HNO 2 concentration in the solution. The HNO 2 did not appear (i.e., [HNO 2 ] < 2 x 10 -4 M) in the dissolution of a UO 2 pellet (∼1g) with a low dissolution rate, 0.4 g/h of UO 2 at 100°C. When high concentrations of I 2 and NO 2 (263 parts per million of I 2 and 38% of NO 2 ) in an N 2 flow were passed through a simulated spent-fuel solution at 100°C, the predicted colloid of AgI was produced as a chemical equilibrium product of the reaction AgI(s) + 2HNO 3 (aq) = 1/2I 2 (aq) + AgNO 3 (aq) + NO 2 (g) + H 2 O(l). This finding suggests that colloidal iodine may be produced secondarily in the dissolver of reprocessing plants; this can be one of the reasons why the residual iodine quantity in spent-fuel solutions is higher in reprocessing plants than in laboratory-scale experiments.

Effects of gamma rays on etching of heavy ion tracks in polyimide

Abstract It was found that exposure of polyimide, bombarded by heavy ions, to gamma rays in the presence of oxygen increased the emergence of etched heavy ion tracks. The degree of increase was larger for the lighter ions than for the heavier ions. The effect was remarkable only for the track etching rate and the large ratio of V t V g obtained. At doses of more than 4 × 108 rad the track etching rates converge to a certain value, regardless of the kind of ions. The presence of oxygen during gamma-ray exposure was considered to inhibit cross-linking and form some oxygenated compounds in the polymer that accelerate the dissolution of the tracks.