Tsutomu Sakurai

Summary on international benchmark experiments for effective delayed neutron fraction (βeff)

Abstract To improve the accuracy of prediction of βeff, an international program of benchmark experiments was planned. This program consisted of two parts; the BERENICE-MASURCA and the FCA XIX series of experiments. The former was carried out in the fast critical facility MASURCA of CEA, FRANCE between 1993 and 1994. The latter one was carried out in the FCA, JAERI between 1995 and 1998. In these benchmark experiments, various experimental techniques were applied to measure the βeff. Through the synthesis of the different results, a recommended value for each core was provided and the accuracy of the measurements was evaluated to be better than 3%. The calculations showed good agreement of the recommended βeff values within 3% for JENDL-3.2 and ENDF/B-VI delayed neutron data sets.

Behavior of ruthenium in fluoride-volatility process—II. Fluorination of RuO2 by F2

Abstract RuO 2 was fluorinated by F 2 in the temperature range 250–500°C. Mass spectrometry confirmed that the reaction product was RuOF 4 . Small amount of RuO 4 was produced as a by-product in the fluorination. Temperatures higher than 400°C were necessary to convert RuO 2 smoothly into RuOF 4 . IR absorption spectrum of RuOF 4 was obtained. The product is an unstable material and tends to decompose into RuF 4 , releasing oxygen. Discrepancies with earlier published literature were discussed.

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...

Behavior of ruthenium in fluoride-volatility processes—V conversions of RuOF4, RuF4, and RuF5 into RuO4

Abstract RuOF 4 , RuF 5 and RuF 4 are convertible almost completely into RuO 4 at room temperature by the repetitions of the operation consisting of their hydrolysis and the subsequent treatment of the hydrolysis products with F 2 . This is because their hydrolysis products, a large portion of which is in the form of ruthenium hydroxides, are dehydrogenated by F 2 at room temperature to produce RuO 4 , e.g. Ru(OH) 4 − yH 2 O + (2+ y)F 2 →RuO 4 +2(2+ y)HF + y 2O 2 . Since the hydrolysis products dehydrate progressively on heating, these conversions are achieved most effectively at room temperature. Mass spectrometry, IR analysis, and thermal analysis were applied to confirm these processes.

Decompositions of carbon dioxide, carbon monoxide and gaseous water by microwave discharge

Conditions for the effective decompositions of CO2, CO and H2 0(g) in microwave discharge (20–100 W) were studied in a flow method, in connection with fixation of 14C (in CO2). Carbon dioxide of 0.41 to 1.34 kPa was decomposed into CO in 73–92% yield in the linear gas velocity range of 0.01 to 0.56 m/s (the residence time in plasma, 4.50 to 0.08 s). For 0.83 kPa CO2, the maximum value of 92% was obtained at 0.04 to 0.06 m/s, and further increase in the linear gas velocity to 0.56 m/s decreased the yield to about 80%. Only 5% or less of CO (0.82 kPa) was converted to carbon under the same condition as above. Almost 100% of H20(g) of 0.82 kPa was decomposed into H2 and O2 at 0.60 m/s (the residence time, 0.08 s) and 50 W. The effective decomposition of H2 0(g) needs such a high linear gas velocity to suppress the reverse reaction. The use of the appropriate linear-gas-velocity is important for the effective decompositions of CO2 and H2 0(g). The reaction of H2 with O2 to form H2O proceeds at temperature as low as 293 K on SUS and Cu metal surfaces; this phenomenon was applied to analysis of the decomposition of H2O(g).

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...

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.

Buffer gas effect on monitoring I2 by a laser induced fluorescence method

Abstract Based on the measured N 2 pressure dependence of high resolution fluorescence excitation spectra for 127 I 2 near the He-Ne laser frequency, effects of the N 2 pressure on the I 2 detection limit and isotopic selectivity of an on-line I 2 monitor using a laser induced fluorescence method are discussed. A possible influence from NO 2 , which is contained in reprocessing off-gas streams, on monitoring I 2 is also examined. The 127 I 2 in N 2 at atmospheric pressure is detected down to a concentration of 5 × 10 12 molecules cm −3 by a 3 He- 20 Ne laser induced fluorescence method.

Fluorination of Uranium Compounds by Bromine Trifluoride Vapor, (I):Fluorination of U 3 O 8

The fluorination of U3O8 powder by BrF3 vapor was attempted. The reaction proceeded even at 67°C and under 10 mmHg BrF3 partial pressure, producing UF6. The reaction rate increases with temperature...