Showing papers in "Journal of Nuclear Science and Technology in 1992"

Effect of Dry Density on Diffusion of Some Radionuclides in Compacted Sodium Bentonite

Abstract: Apparent diffusion coefficients were measured at room temperature under atmospheric condition by one-dimensional non-steady state diffusion for 3H, 90Sr, 99Tc, 129I, 137Cs, 237Np and 241Am in water-saturated compacted sodium-bentonite whose dry densities were 0.2–2.0 (x103kg/m3). Dry density of bentonite affected the diffusivity for the radionuclide and the apparent diffusion coefficient decreased with increasing dry density of bentonite. Small effect of dry density of bentonite on retardation factor which was derived from the apparent diffusion coefficient was indicated for 137Cs, 90Sr, 99Tc and 129I. On the other hand, the retardation factors of 237Np and 241Am showed a tendency of increasing with dry density of bentonite. Dominant chemical species of 237Np and 241Am in the pore water of bentonite were estimated NpO2(CO)3 5- and AmOH(CO3)3 2-, respectively and they possibly formed large anion. Distribution coefficient derived from the apparent diffusion coefficient showed a tendency of decreasing with i...

Vectorization of Continuous Energy Monte Carlo Method for Neutron Transport Calculation

Abstract: The vectorization method was studied to achieve a high efficiency for the precise physics model used in the continuous energy Monte Carlo method. The collision analysis task was reconstructed on the basis of the event based algorithm, and the stack-driven zone-selection method was applied to the vectorization of random walk simulation. These methods were installed into the vectorized continuous energy MVP code for general purpose uses. Performance of the present method was evaluated by comparison with conventional scalar codes VIM and MCNP for two typical problems. The MVP code achieved a vectorization ratio of more than 95% and a computation speed faster by a factor of 8–22 on the FACOM VP-2600 vector supercomputer compared with the conventional scalar codes.

Irradiation Effects on Corrosion Resistance and Microstructure of Zircaloy-4

Abstract: In order to investigate irradiation effects on nodular corrosion resistance of Zircaloy-4, an out-of-pile corrosion test was conducted using Zircaloy-4 specimens cut from the channel box of a fuel assembly irradiated in the BWR (Monticello reactor) up to the neutron fluence of 1.53×1026 n/m2 (E>1MeV). The corrosion test was carried out in high pressure steam of 10.3 MPa at 783 K for 24 h. No nodules appeared on the specimens cut from welded areas of the channel box and nodular corrosion resistance tended to be better with increasing neutron fluence. Microstructural evolution in the form of irradiation-induced release of Fe atoms from Zr(Fe, Cr)2 type precipitates was detected by an analytical electron microscope. It was found that the higher the concentration of dissolved Fe and Cr in the grains of Zircaloy-4, the better the nodular corrosion resistance.

Effects of Thermal Annealing on the Macroscopic Dimension and Lattice Parameter of Heavily Neutron-Irradiated Silicon Carbide

Abstract: Reaction-sintered β-SiC specimens were neutron-irradiated in fast breeder reactors to fluences from 3.0×1024 to 1.7×1027 n/m2 (E>0.1 MeV) at temperatures from 370 to 620°C. Irradiation to fluences above 4.8×1026 n/m2 caused swelling (growth) that was significantly greater in respect of macroscopic dimension than of lattice parameter. These highly irradiated specimens also showed significant broadening of their X-ray line profiles, accompanied by generation of interstitial dislocation loops. Upon annealing, all specimens, irrespectively of the fluence to which they had been irradiated, tended toward recovery of their swelled macroscopic dimension and lattice parameter. This tendency was initiated when the annealing temperature exceeded that of irradiation, with the percentage of residual swelling lowering roughly in proportion to annealing temperature. The more highly irradiated specimens, in which the macroscopic dimension had swelled significantly more than the lattice parameter, lowered their percentage...

Adsorption Characteristics of Water Vapor on Gamma-Lithium Aluminate

Abstract: Lithium aluminate (LiAl02) is one of the probable candidates for tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stabilit...

Direct Cycle Light Water Reactor Operating at Supercritical Pressure.

Abstract: The concept of a direct cycle light water reactor (LWR) operating at supercritical pressure is presented. It is attractive for improving the thermal efficiency of LWRs and for simplifying the reactor system(1). The critical pressure of water is 22.1 MPa (221 bars). The density of water changes continuously above it and the concept of boiling does not exist. The system is conceptually depicted in Fig. 1. The water coolant which flows into the core is heated up and can be directly fed to turbines. Compared with the current BWRs, the recirculation system and steam separators and dryers will be eliminated. The vessel size will be greatly reduced. This will reduce the capital cost. The thermal efficiency will be also revolutionally improved. The feasibility of the system was studied through the conceptual design of the core.The axial temperature and density distribution of the coolant in the core were calculated at 25 MPa (250 bars) using a single channel model of a fuel and coolant. The density decreases continuously from the inlet (0.725 g/cm3) to the outlet (0.137 g/cm3) and the temperature increases from 583 K (310°C) to 689 K (416°C). The heat is efficiently removed due to the high specific heat of water around 658 K (385°C). The density change is mild at 250 bars than 225 bars which is close to the critical pressure. It is desirable to choose 250 bars for the stability of the flow in the core.

Macroscopic Cross Section Measurements and Defect Detection in Materials Using Neutron Radiography Technique

Abstract: Neutron radiography (NR) technique was applied to analyze behaviors of thermal neutrons in slabs, which have a wide range of the ratio r, of scattering to non-scattering cross sections. Transmittances were measured for various materials as basic data for NR study. Scattering components were estimated and subtracted from observed neutron intensities measured behind slabs. Effective total macroscopic cross sections were estimated and were found they agreed with given values of ASTM E748-80 within ±20%. Defects (voids and impurities) were also analyzed, and their detection limits for thickness t were estimated for materials of various r as a function of t.

Gadolinium Isotope Separation by Cation Exchange Chromatography.

Abstract: Displacement chromatographies of Gd adsorption band in cation exchange resin were performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagents. The heavy isotope of 160Gd was found to be enriched at the front boundary of Gd adsorption band and the lighter isotopes of 1MGd, 156Gd and 157Gd were enriched at the rear boundary in both cases of 20.1m elution with EDTA and 14 m elution with malic acid, as predicted in the theoretical relations. Observed separation coefficients are 4.9×10−5, 4.0×10−5 and 2.5×10−5for isotopie pairs of 156 160Gd, 158Gd and 160Gd, respectively, in the case of EDTA elution. In the case of malic acid elution, smaller separation coefficients were observed as 1.8×10−5, 1.6 5O−5 and 0.92×10−5 for isotopie pairs of 156 160Gd, 157Gd and158 160 respectively.

Development of ZnS(Ag)/NE102A and ZnS(Ag)/Stilbene Phoswich Detectors for Simultaneous α and β(γ) Counting

Abstract: (1992). Development of ZnS(Ag)/NE102A and ZnS(Ag)/Stilbene Phoswich Detectors for Simultaneous α and β(γ) Counting. Journal of Nuclear Science and Technology: Vol. 29, No. 9, pp. 927-929.

Precipitation Behavior of Platinum Group Metals from Simulated High Level Liquid Waste in Sequential Denitration Process

Abstract: The precipitation behavior of the platinum group metals from a simulated high level liquid waste (HLLW) was experimentally examined in a sequential denitration process with formic acid. The precipitation fractions of Ru, Rh and Pd were found to depend on pH of the denitrated solution. The precipitation fractions of Ru and Rh increased linearly with pH of the denitrated solution and became more than 98% over pH 7, and almost all Pd was precipitated at pH around 2. Results showed that more then 98% of Rh and Pd and about 80% of Ru could be recovered as precipitates from HLLW, by means of the sequential denitration process.

Rigorous Derivation of Multi-Point Reactor Kinetics Equations with Explicit Dependence on Perturbation

Abstract: Nodal kinetic equations for coupled reactors, namely multi-point reactor kinetics equations whose dependent variables are the fission sources of each reactor are derived rigorously, using kinetics parameters with the explicit dependence on a perturbation, from the time dependent multi-group diffusion equation. Exact expressions for the coupling coefficients, neutron life time and the change of the coupling coefficients due to the perturbation are given. Since the present equations are exact independent of the strength of the coupling, these equations can be used for any reactor by dividing a core into appropriate subregions. Some analytical expressions of the coupling coefficients, neutron life time and other kinetics parameters are given for some simple geometries.

Mean Atomic Velocities of Uranium, Titanium and Copper during Electron Beam Evaporation

Abstract: Mean atomic velocities of uranium, titanium and copper during electron beam evaporation of the metal were measured by a microbalance technique as a function of evaporating metal surface temperature. In the measured temperature range, the mean velocity of uranium was up to 2.1 times the thermal mean velocity vth, corresponding to the surface temperature of the evaporating metal. Mean velocities of titanium and copper increased to 1.6 and 1.3 times vth, respectively. This meant that mean velocities of uranium and titanium exceeded the maximum flow speed of an ideal gas in adiabatic expansion, i.e. 1.4 times vth, while the mean velocity of copper was almost equal to it. The electronic states of uranium and titanium were thermally excited to higher levels, then such excited energy should be converted to kinetic energy during adiabatic expansion. However, copper was rarely excited to higher levels because of the their fewer number. As a result, mean velocities of uranium and titanium were faster than the maxim...

Evaluation of Carburization and Decarburization Behavior of Fe-9Cr-Mo Ferritic Steels in Sodium Environment

Abstract: Carburization and decarburization behavior in sodium have been examined for Fe-9Cr-Mo ferritic steels exposure to flowing sodium with containing 0.0049, 0.016 and 0.16 wppm carbon at temperatures between 723 and 873 K. The Fe-9Cr-Mo ferritic steels were more resistant to carbon transfer than 2 ¼ Cr-lMo steel. The carbon transfer and its gradient in Fe-9Cr-Mo ferritic steels was closely related with carbon concentration in sodium, and carburization and decarburization behavior depended on the sodium conditions. In the case of the application of Mod. 9Cr-lMo steel to heat transfer tubes of steam generator of LMFBR, carburization behavior was observed on the conditions that sodium inlet temperature was 778 K and carbon concentration in sodium was 0.01~0.10 wppm. The mean carbon contents of heat transfer tubes after the operation of the steam generator for 200,000 h were estimated to be about 0.103~0.148 wt% comparing with initial carbon contents of 0.10 wt%. Consequently it is expected that high-temperature ...

Experimental Study of Dust Behavior during Depressurization

Abstract: A small amount of graphite dust is present in the primary cooling system of a graphite, moderated gas-cooled reactor during normal operation and condensable fission products may be absorbed on the dust. Since it is possible that the fission products are released with dust under the accident conditions such as depressurization events, they have a potential hazard of radiation exposure to the environment. In order to obtain liftoff fractions (fractional amount removed) of the graphite dust during the depressurization, an investigation was performed by the blow down test. In the test, graphite powder attached on the sample was blown down under the high speed gas flow to simulate flow condition during the depressurization accident. According to the shear ratio concept, the liftoff fraction can be described by shear ratio, which is defined as the ratio of wall shear stress in the blow down condition to the normal condition. From the test result, it is concluded that the shear ratio concept is not completely en...

Feasibility of Fast Fission System Confining Long-Lived Nuclides

Abstract: The feasibility of fast fission system confining long-lived nuclides without other supporting system as synergetics for fuel sustainment and waste incineration was studied from the aspects of nuclear material balance and neutron economy. The continuous utilization of fast fission system which confines all actinides in the reactor but discharges all FP will lead to huge accumulation of radioactive wastes such as 129I, 135Cs, 107Pd, 93Zr, 99Tc, 126Sn and 79Se in the far future. Then we studied the feasibility of the system that these long-lived seven FP are also confined in the reactor with actinides. In this scheme, all the long-lived nuclides to be disposed of were exposed with neutrons in the reactor and removed as different nuclides after nuclear transmutation. As the wastes stored in the repository was composed of only shorter-lived nuclides, total amount of radioactive wastes in the repository was suppressed to be less than a few tons per 3 GWt reactor.

Theory of Ion-Extraction Time from a Plasma by a Static Electric Field

Abstract: When a static electric field is applied to a plasma, plasma ions are extracted and collected on the wall biased with a lower potential. The author derived a simplified formula to evaluate the ion-extraction time from a slab plasma created between the parallel plates. This formula is applicable over a wide density range.

Development of a Supermirror Neutron Guide Tube

Abstract: A supermirror neutron guide tube with a characteristic wavelength of 1.2 A was developed and installed at the Kyoto University Reactor (KUR). The apparent critical wavelength of the present supermirrors is about 250 A. The geometrical parameters of the guide tube are: 11.7 m total length, and 10 mm wide X74 mm high beam cross section. The supermirror neutron guide tube presents decisive advantages over the conventional nickel mirror guide tube higher transmission of neutrons, brought about through the contribution of neutrons of shorter wavelengths and of those presenting large divergent angles. The total neutron flux obtained from the KUR supermirror guide tube is about 5x107n/cm2·s, which is about 25 times what is obtainable with the conventional KUR nickel mirror neutron guide tube of the same geometrical parameters.

Underwater Cutting of Reactor Core Internals by CO Laser Using Local-Dry-Zone Creating Nozzle

Abstract: With a view to practical application of the CO laser to underwater cutting of thick steel plates, a nozzle for creating a local dry zone on the workpiece has been developed and tested. The nozzle directed against the workpiece surface discharges a jet of air, which forms the local dry zone, bounded by a cone of high-speed water jet discharged from a concentric annular outlet. Preliminary tests were performed to optimize the nozzle shape and operating conditions. The resulting nozzle was used with a 5 kW CO laser for actual underwater cutting tests on stainless steel plates: Entirely satisfactory cutting performance was confirmed on various workpiece geometries and working positions.

Solvent Extraction of Np (V) with CMPO from Nitric Acid Solutions Containing U (VI)

Abstract: The extraction of Np(V) in the presence of U(VI) or Nd(III) was studied with 0.2 M CMPO- decalin and with 0.2 M CMPO-1.4 M TBP-n-dodecane. Distribution ratios of Np(V) decreased with increasing the concentration of Nd(III), which was considered to be explained by the decrease in the concentration of free CMPO. On the other hand, distribution ratios increased as the concentration of U(VI) increased. The absorption spectrum of Np(V) in organic solution showed a new absorption peak which was probably attributable to the formation of cation-cation complexes of Np(V) and U(VI). Assuming the formation of cation-cation complexes, the dependence of distribution ratio of Np(V) on the concentration of U(VI) was found to be semi-quantitatively explained.

Experimental Study of CR-39 Etched Track Detector for Fast Neutron Dosimetry.

Abstract: The CR-39 detectors were irradiated with three kinds of fast neutrons and etched in several alkaline solutions. Size distributions of etch-pits were obtained from analysis of micro- photographs. An automatic image analyzer was used to obtain the density of etch-pits. When etching conditions were kept at 30% KOH, 90°C and 1 h. the sensitivity was found to be 3.8xlO−4, 4.9 xlO−4 and 2.4 x10−4for fission, Am-Be and 14 MeV neutrons, respectively. From analysis of increasing rate of the sensitivity, it was found that the track density in CR-39 roughly corresponded to the density of elastic scattering with H, C and O in the case of Am-Be and 14 MeV neutrons, however, the track density was somewhat smaller than the elastic scattering density in the case of fission neutrons. The size of etch-pits increased with neutron energy. The etching time could be reduced to less than 1/10 as a result of a rising from 60 to 90°C. After due consideration of background counts, a dose equivalent of 0.2 mSv could be measured wit...

Oxidation of Pentavalent Neptunium by Nitrous Acid in CMPO-TBP-n-Dodecane Organic Solution

Abstract: The oxidation of Np(V) by nitrous acid was investigated spectroscopically in 0.2 M CMPO—1.4 M TBP—n-dodecane and the oxidation rate constant of Np(V) was estimated assuming the first-order reaction. By using the obtained oxidation rate constant as well as taking account of the Np(V) oxidation in aqueous phase and the distribution ratios of Np(V) and Np(VI) cited from literature, extraction kinetics of Np from 4 M nitric acid solution was calculated, and was compared with the extraction kinetics measured experimentally.

JENDL-3 Fission Product Nuclear Data Library

Abstract: Neutron nuclear data in the energy range between 10−5 eV and 20MeV have been evaluated for 172 nuclides from 75As to 169Tb in the fission product mass region to provide data for the JENDL-3 fission product nuclear data library. Evaluation was made on the basis of recent experimental data reported up to 1988 and the nuclear model calculations. Resonance parameters have been evaluated on the basis of measured data set and a REPSTOR system developed in JAERI. The spherical optical model and statistical theory were applied to calculation of the total, capture, elastic and inelastic scattering cross sections, and the multistep evaporation model and pre-equilibrium theory were used for threshold reaction cross section calculations. For the even-even nuclides around fission yield peaks, direct inelastic scattering cross sections were calculated with the distorted wave Born approximation. Nuclear model parameters, such as optical model parameters, level density parameters, x-ray strength functions and Kalbach con...

Experimental and Analytical Studies of Flow Instabilities in Pressure Tube Type Heavy Water Reactors

Abstract: The aims of the study are to correlate instability data in ATR (Advanced Thermal Reactor) channels using dimensionless parameters, and validate the ATRECS-II code. Various kinds of experiments were conducted with the 14 MW Heat Transfer Loop (HTL) and the 6MW ATR Safety Experimental Loop (SEL). Experimental ranges of parameters are listed below: — Natural circulation or forced circulation with channel flow rate of 0.5~3.6kg/s Pressure ranging 0.2~7 MPa — Subcooling ranging 5~70°C — Outlet pipe of 9 m in length and 5 in. in diameter, or 25.5 m in length and 3 in. in diameter — Axial power distributions of 3.7 m heaters are uniform, inlet peak and so on. For relatively high exit steam quality conditions (Type-II), instability boundaries are obtained as a function of exit quality and Reynolds number at the core inlet by processing various data, and cladding dryout occurs in conjunction with the Type-II instability. There is another type of instability (Type-I) at the nearly zero exit quality region. In this ...

Selective Exchange of Pu4+ and Am3+ by Titanium and Tin Antimonates Cation Exchangers

Abstract: The selectivity for Pu4+ and Am3+ has been studied as a function of [HNO3] on titanium and tin antimonates cation exchangers at 30°C A large selectivity toward Pu4+ and Am3+was discovered on tin and titanium antimonates cation exchangers, while they showed low selectivity for 4f elements such as La3+ and Nd3+ The log-log plot of the distribution coefficients vs [HNO3] showed the linear relationship with a slope nearly equal to the valence of exchanging ions It indicates that the adsorption predominantly proceeds through the ion exchange The ion-exchange rate in the initial stage of adsorption was about the same as that of a commercial strong acid-type organic cation exchange resin Highly selective uptake of Pu4+ has also been demonstrated in a simulated high level nuclear waste solution containing 05 M HNO3

Migration of Cesium, Strontium and Cobalt in Water-Saturated Inada Granite

Abstract: Diffusivities of Cs, Sr and Co were measured in a water-saturated granite in an attempt to investigate the migration of radionuclides into the matrix of the rock. The measured penetration profiles of every tracer were composed of two parts. There were a steep slope near the surface and a gradual slope in the deeper part. These profiles were successfully explained by considering two diffusion paths in the granite. One diffusion path was fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for all nuclides were 10-11 to 10-12 m2/s through the fissure and 10-14 m2/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This calculated ratio suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.