Showing papers in "Journal of Nuclear Science and Technology in 1987"

Immobilization of Cesium into Pollucite Structure by Hydrothermal Hot-Pressing

Abstract: In order to immobilize Cs into pollucite structure, hydrothermal reactions of Cs with amorphous aluminosilicate (siliceous sinter) and with mixtures of low-quartz (silicastone) and Al(OH)3, were performed. In both cases, pollucite was formed in 5-N NaOH solution above 200°C for 10 min. Synthesized pollucite was solid solution between pollucite and analcite. Waste forms in which Cs was immobilized in pollucite structure were successfully produced by the hydrothermal hot-pressing method using the silica matrix (mixture of low-quartz and amorphous aluminosilicate) containing Al(OH)3 and NaAlO2. Effect of hot-pressing conditions on leachability of the waste forms was investigated. The waste form containing 10w/o CsOH produced at 300°C and 49 MPa for 24 h, had Cs leach rate of 3.15 g/m2·d by Soxhlet leach tests for 7 d. The waste form was porous, but had high compressive strength and thermal stability.

Thermal Creep of Zircaloy-4 Cladding under Internal Pressure

Abstract: Creep characteristics of Zircaloy-4 stress-releaved cladding under internal pressure were studied. Creep tests were conducted under 21 conditions chosen from the temperature range of 603∼693 K and the hoop stress of 49∼314 MPa. The maximum accumulated test period was 3,000 h. Diametral creep data were analyzed by separating the primary (transient) and the secondary (steady-state) creep, based on Darn's quasitheretical model, and the following equations were derived: Total creep strain: e= eS P {1--exp(−-52( s t)0.5)}+ s t Saturated primary creep strain: eS P=2.16 × 10−2 ( s cal)0.109 Steady-state creep rate: s= 1.57 × 1013(E/T) {sinh(1.13 × 103σ/E)}2.1exp (−-2.72 × 105/RT). The apparent activation energy of the steady-state creep, which is 2.72 × 105 J/mol, is in good agreement with these of self-diffusion of Zr in Zr-Sn alloys and suggests the self-diffusion is the control mechanism.

Influence of Functional Sulfonic Acid Group on Pyrolysis Characteristics for Cation Exchange Resin

Abstract: Pyrolysis of spent ion exchange resins is used to reduce radioactive waste volume and to make the final waste form more stable. The weight loss of cation exchange resin after pyrolysis is only 50w/o, while that of anion exchange resin is 90w/o. Fundamental experiments were performed to investigate the reason for the small weight loss of the former. The cation resin consists of base polymer and functional sulfonic acid groups. Chemical analyses of the pyrolysis products showed that 65% of the functional groups decomposed at about 300°C and generated SO2 gas. However, only a small amount of the base polymer was pyrolyzed even at 600°C and the weight loss was only 50w/o. The IR and XPS studies on the residue showed that 35% of the functional sulfonic acid groups was converted to sulfonyl and sulfur bridges between the base polymers during pyrolysis. These bridges made the base polymers thermally stable. Therefore, the small weight loss of the cation resin was attributed to formation of bridges, which origina...

Empirical Formulas for 14-MeV (n, p) and (n, α) Cross Sections

Abstract: Empirical formulas for the 14 MeV (n, p) and (n, α)cross sections given by Levkovskii were modified separately In three ranges of mass number, in each of which, coefficients modifying Levkovskii's formulas were determined by least-squares fitting to experimental cross sections. The resulting modified formulas yielded cross sections representing markedly smaller chi-square deviations from experimental values, and moreover gathered closer to unity, compared with calculation using Levkovskii's original formulas.

Drift-Flux Parameters for Upward Gas Flow in Stagnant Liquid

Abstract: The drift-flux model is widely used for gas-liquid two phase flow analysis, because it is applicable to various flow patterns and a wide range of void fractions. The drift- flux parameters for upwa...

Extraction of Pentavalent Neptunium with Di-Isodecyl Phosphoric Acid

Abstract: As a fundamental study for separating neptunium from high-level radioactive waste, the mechanism and the rate of extraction of pentavalent neptunium with DIDPA were investigated. From the analysis of oxidation state of neptunium in organic phase, it was proved that disproportionation reaction of Np(V) was concerned in the extraction. The reaction order of the extraction with respect to neptunium concentration was larger than unity. The extraction rate was much reduced by the decrease of DIDPA concentration. The dependence of the rate on nitric acid concentration and on the temperature was also examined.

Reduction of Plastic Anisotropy of Zircaloy Cladding by Neutron Irradiation, (II)

Abstract: Initial plastic deformation behavior of zirconium alloy fuel cladding was described quantitatively by the deformation system of single crystal of α-zirconium, and a model was proposed to simulate the yield behavior of polycrystalline material. Based on the model, effects of crystallographic texture and stress state on the plastic deformation of the cladding were evaluated. Conclusions obtained from this investigation are: (1) The proposed model shows good agreement with the von Mises' yield criteria for a material with isotropic properties. (2) Plastic anisotropy of the cladding decreases when neutron irradiation affects prism slip more strongly than the other deformation systems. (3) Dominant deformation systems for axial tension or internal pressurization of the cladding are predicted to be prism slip or tensile twin, respectively, when the stress state of the cladding reaches the yield condition.

Numerical calculation of concentration profiles within thermal diffusion column with continuous feed and draw-offs.

Abstract: Axisymmetric concentration profiles of an isotope separating thermal diffusion column with continuous feed and draw-offs were calculated by solving the convection-diffusion equation using Newton iterative method, where the flow variables are specified from the input data. Computations were performed for 36Ar gas mixture within and 40Ar the cylindrical column having inner hot radius of 0.15 mm and an outer cold radius of 7.5 mm, between which the temperature differs by 515 K. The rate of feed F, supplied into the middle-height point of the column, was varied from 2.72 × 10−4 g/s (10 cm3/min at 25°C) to 5.45 × 10−3 g/s (200 cm3/min), while the cut θ, or the ratio of the upper drawing-off to feeding rates, from 0.1 to 0.9. The pattern of concentration profile depends largely on the value of the total transport (that is, θ F in the upper section and --(1--θ) F in the lower section), and the two different patterns are linked at the feed point. The effect of changes in hot wire temperature (723∼973 K, temperatu...

Radiolytic Gas Production from Tritiated Water Adsorbed on Molecular Sieve 5A

Abstract: Hydrogen evolution from 60Co γ- and 3H β-irradiated molecular sieve 5A adsorbing HTO was measured. The results showed an additional evolution of H2(HT) gas due to energy transfer from molecular sieve to adsorbed water in both γ- and β-irradiations, and the yield at a given irradiation dose was higher than that from radiolysis of liquid HTO but lower than that in the silica gel-HTO system. The additional yield was formulated as a function of the amount of adsorbed water and irradiation dose. However a large difference in hydrogen yields was observed between γ- and β-irradiations contrary to silica gel-HTO system. A possible reason is considered.

Reduction of plastic anisotropy of Zircaloy cladding by neutron irradiation. I. Yield loci obtained from Knoop hardness

Abstract: Mesure de la durete Knoop pour etudier l'anisotropie plastique des tubes a combustible irradies. Influence de la direction de l'indentation sur la durete. Effet de la fluence de neutrons sur la durete, et sur l'anisotropie plastique. Analyse de l'anisotropie plastique dans des tubes non irradies

BWR Plants with Low Shutdown Radiation Level: Design and Construction of Plants and Current Experience with Occupational Exposure of Plants

Abstract: Occupational exposure during BWR refueling and annual maintenance periods is determined by radioactive corrosion products, such as 60Co and 58Codeposited on major components and piping of the primary cooling system The authors have investigated behavior of radioactive corrosion products, eg generation, activation and deposition processes, in the primary cooling system, and then ex- pressed the findings as mathematical equations These provide corrosion product simulation models to predict the amounts of radioactive corrosion products depositing on components and piping The effects of corrosion product reduction procedures on shutdown dose rate were evaluated using the model The procedures were incorporated into the Japanese Improvement and Standardization Program Improvements of operational procedures to control water chemistry, such as Ni/Fe ratio, as well as application of hardware improvements resulted in an extremely low occupational exposure of less than 90 man-rem/yr for currently constructed

Surface effects in simultaneous ion- and gas-driven hydrogen isotope permeation of nickel.

Abstract: Recombination coefficient kR for hydrogen on Ni was evaluated experimentally by measuring the permeation rate of ion-driven deuterium in the temperature range of 573–873 K, with impurities on the specimen surface controlled at nearly the same composition prior to deuterium implantation. Calculation showed that kR ′s of upstream and downstream-side surface had an apparent activation energy of negative values, but of different values, and that of upstream-side surface Increased as much as two orders of magnitude due to the deuterium ion implantation.

Chemical composition of crud depositing on BWR fuel surfaces.

Abstract: Deposition profiles of corrosion products on fuel surfaces and products chemical compositions were determined at Shimane Nuclear Power Plant, a low-crud BWR. The deposited amounts were expressed as functions of crud concentration in the reactor water, fuel burnup and flow velocity in a fuel channel. The results could be predicted satisfactorily by the crud deposition model based on microlayer evaporation and drying out phenomena. The amount depositing at high flow velocity gave saturated values which were inversely proportional to the flow velocity (∝ 1/v), while those at low velocity did not reach saturated values, but rather were proportional to 1/v 3. The depositing corrosion products could be divided into two layers, inner and outer, with more Co ions being taken into the former layer.

Leach Rates of Composite Waste Forms of Monazite- and Zirconium Phosphate-Type

Abstract: Leaching behavior of simultaneously synthesized composite waste form of monazite- and zirconium phosphate-type was investigated by making use of simulated high level waste (HLW). The obtained results showed that the leach rates of the composite forms are very low compared to that of the borosilicate glass waste form, indicating that the composite is regarded as being significant to immobilize HLW grossly like vitrification.

Water Quality Control at Primary Cooling System of Crud Concentration Suppressed Boiling Water Reactor, (II): Evaluation of Cobalt-58 Behavior in Iron Crud Suppressed BWR

Abstract: A possible accumulation mechanism of Ni and radioactive 58Co ions in the reactor water of a low iron crud concentration plant was modeled based on a direct deposition of Ni ion on fuel cladding surfaces as a form of NiO, followed by the solid phase reaction between NiO and iron crud (α-Fe2O3) to produce NiFe2O4. The calculated results agreed satisfactorily with measurements in the first Japanese standard BWR, Fukushima 2-2 (1,100 MWe). These calculations showed that controlling the Fe/Ni corrosion products ratio in the feed water to a value larger than 2 was effective to suppress 58Co activity in the reactor water as well as Ni ion concentration.

Radiolytic Environments in Boiling Water Reactor Cores

Abstract: Radiolytic, environments in the BWR primary system were evaluated by using a theoretical model. Reactor core was divided into two regions, boiling and by-pass (non-boiling) channels. The major findings are summarized as follows: (1) Under normal operation without hydrogen addition, dissolved hydrogen and oxygen concentrations had their maximum values at the height where boiling started. Their concentrations in the boiling channel were lower than those in the by-pass channel because of hydrogen and oxygen release from liquid phase to gas phase. (2) The most efficient oxygen suppression by hydrogen addition was expected in the non-boiling regions of the reactor core where injected hydrogen was confined in the liquid phase. (3) When the bulk decomposition of water in the reactor core is represented by the coefficient decreased as hydrogen injection rate increased, but B hardly changed at a low hydrogen addition rate.

Uranium adsorption properties of hydrous titanium oxides in seawater.

Abstract: Some characters on micro structure and chemical composition of hydrous titanium oxide (HTO) and its granules crosslinked with polyacrylic acid hydrazide (PAH) were measured. And by using agitated tank system, seawater uranium adsorption properties of HTO and its granules were evaluated. Based on these results, the mechanism of adsorption and the effect of granulation were discussed. Pore diffusion appeared to occur in macro pore and adsorption seemed to occur mainly on inner surface of the macro pore. The pore diffusion coefficient and adsorption capacity of the granulated HTO were found to be little affected by crosslinking or by granule diameter. With increase of granule diameter the liquid-film mass transfer coefficient of the crosslinked granule increased. It was shown that PAH is a binder with good seawater permeability.

New method to analyze equilibrium cycle of pebble-bed reactors.

Abstract: A new computer code PREC was developed to solve neutron and nuclide density distributions at the equilibrium cycle of pebble bed reactors. The PREC code has the following special advantages. 1. To provide a direct solution of the equilibrium cycle 2. To fix the effective multiplication factor as an input 3. To treat continuous fuel movement 4. To treat r-z two-dimensional geometry, leading in turn to the following special advantages: (4-1) Ability to treat the cavity at the top of the core (4-2) Ability to treat the curved fuel stream-line.

CR39-BN Detector for Thermal Neutron Dosimetry

Abstract: A CR-39 plastic track detector has been applied to thermal neutron dosimetry by combining with a converter using (n, α) reactions. A ceramic boron nitride (BN) was utilized as the promising converter because of high boron-concentration and its smooth surface. The contribution of background tracks was evaluated in the region of CR-39 plastic unattached to BN converter. The detector was exposed to a reference neutron field generated by 252Cf source in a water tank in order to investigate the detection characteristics. It was found that the efficiency was (1.0 ± 0.1) × 10−3 pits/n, corresponding to the sensitivity of (9.6 ± 0.9) × 102 pits/mm2/mSv. The linear response was experimentally confirmed between 0.035 and 0.7 mSv. The minimum detectable dose equivalent was also estimated to be about 0.005 mSv.

Improvement of Accuracy of Zr/Nb Activation-Rate Ratio Method for D-T Neutron Source Energy Determination

Abstract: (1987). Improvement of Accuracy of Zr/Nb Activation-Rate Ratio Method for D-T Neutron Source Energy Determination. Journal of Nuclear Science and Technology: Vol. 24, No. 12, pp. 1076-1079.

Cross Section Measurements of 27Al(n, α)24Na and 56Fe(n, p)56Mn Reactions for Neutron Energies between 14.0 and 19.9 MeV

Abstract: Cross sections of the 27Al(n, α)24Na and 56Fe(n, p)56Mn reactions were measured precisely by foil activation in the energy range of 14.0 ∼ 19.9 MeV. For the lower energies of 14.0 ∼ 14.8 MeV, the neutron fluence rate was determined by associated α-particle counting, while the proton-recoil telescope was used for the higher energies of 15.2 ∼ 19.9 MeV. Correction was applied to account for the additional radioactivity brought by d + D neutrons from deuteron implantation in tritium target. The 24Na and 56Mn activities generated by the reactions of interest were determined using 4πβ-γ coincidence counter. In respect of the 27Al(n, α)24Na reaction, the present results agree well with the latest evaluations of Asami and Vonach and with Ryves' measurements, except in the higher energy regions, and in respect of the 56Fe(n, p)56Mn cross section, with Ryves' measurements. On the other hand, the ENDF/B-V evaluations deviate appreciably from the present results in respect of both reactions, and this applies also to...

Natural convection heat transfer in thermally stratified liquid metal.

Abstract: Natural convection tests were conducted using Pb-Bi alloy, with the view to evaluating the effects brought by thermal stratification in liquid metal on the natural convection heat transfer along an immersed vertical metal surface. The vertical metal surface was represented by a stainless steel plate 300 mm high, placed in a cylindrical vessel 400 mm in diameter filled with molten Pb-Bi. The experiment was performed with the heat flux of the plate surface maintained constant and uniform. The temperature distribution through the liquid metal filling the vessel was controlled by regulating a flow of air blown onto the vessel surface; temperature measurements were made by means of a traversing thermocouple. For the case of unstratified bulk fluid, the values obtained for heat transfer rate agreed well with corresponding data given by Sheriff for Na. With increasing degree of stratification, the thickness of the boundary layer decreased in keeping. The resulting increase of heat transfer rate indicated a defin...

Structural Material Anomaly Detection System Using Water Chemistry Data, (II)

Abstract: A calculation model was developed to predict the dose rate, caused by 58CO which is formed by the activation of 58Ni, around the recirculation pipes m boiling water reactors (BWRs). The model is characterized by considering direct deposition of Ni ion on the nuclear fuel cladding surface and the geometrical contact probability for the ferrite formation reaction between deposited Ni(Co) and Fe2O3 on fuel cladding surface. This model showed the important role of the amount of Fe crud on the surface to reduce 58CO ion concentration in the reactor water. And the necessary Fe concentration in the feedwater for reducing the dose rate in the primary system was estimated as a function of the operating time. This model also enables the quantitative predictions of the effect of prefilming treatment of the feedwater heater tubes or another methods to reduce dose rate in an Fe crud suppressed BWR.

Effect of Crossflow on Flow Distribution in HTGR Core Column

Abstract: In the thermal hydraulic design of the high temperature gas-cooled reactor core consisting of prismatic fuel elements, the regulation of the coolant leakage flows is very important because these flows decrease the effective flow rate in coolant channels and are considered to be associated with the cause of the column fluctuation phenomenon. An analysis of the coolant flow distribution in the core is carried out by a one-dimensional flow network model. Since it is difficult to model leakage flow paths theoretically, the modelling of the flow network should be based on experiments. In this paper, the air flow test in a full-scale core column with one crossflow gap was carried out to study the effect of the leakage flows on the main coolant channel flows. The numerical results based on the flow network model agreed with the experimental data. Also, it is found that the effect of the leakage flow was large especially in the column with orifices.

Temperature Coefficient of Reactivity in Light-Water Moderated and Reflected Cores Loaded with Highly-Enriched-Uranium Fuel

Abstract: Both experimental and analytical studies have been performed on the temperature coefficient of reactivity in a light-water moderated and reflected core loaded with highly-enriched-uranium fuel, which was constructed in the Kyoto University Critical Assembly (KUCA) The temperature effect on reactivity was measured for the range of 20∼70°C to investigate separately the effects of (1) the fuel pitch (H/235U atomic ratio) and (2) the core shape on this physical quantity The experimental data were analyzed with use of the SRAC code system The calculated eigenvalue k eff agreed with the measured one within 05% in the C/E ratio for both the 2- and 3-dimensional diffusion calculations The experimental data were approximately reproduced by both the eigenvalue and perturbation calculations It was found that the contribution of the core region was negative to the temperature coefficient of reactivity, whereas that of the reflector region was positive The synthesis of these contributions made the temperature c

Core Liquid Level Depression due to Manometric Effect during PWR Small Break LOCA Effect of Core Bypass

Abstract: In the previous study, it is reported that the core collapsed liquid level was depressed nearly to the core bottom and the dryout of the core was observed in the early stage of the PWR cold leg small break loss-of-coolant accident (LOCA) experiment, The manometric effect due to the liquid seal formation in the loop seal and the difference of the liquid holdup between the steam generator (SG) upflow-side and downflow-side caused a depression of the core collapsed liquid level. The core liquid level was recovered just after the loop seal was cleared. The bypass between the core side and the downcomer side affects the core liquid depression. Four 5% cold leg break experiments with the different core bypass location, configuration and size were conducted to clarify the bypass effect. When the bypass was relatively small (less than 3% bypass of the initial core flow before the break), the timing of the loop seal clearing delayed with the bypass. When the bypass was relatively large (9.2% of the core flow), the...

Ion-Exchange Property and Thermal Stability of Hydrous Metal Oxide Ion Exchangers

Abstract: Ion-exchange property and thermal stability were studied on four synthetic hydrous metal oxides from the viewpoint of applicability for the processing of liquid radioactive waste. Hydrous titanium (IV) oxide and hydrous niobium (V) oxide, consisting of metal ions having larger ionic potential, possessed large cation-exchange capacities, and showed high affinity for both the transition metal ions and the representative element ions. Hydrous tin (IV) oxide and hydrous zirconium (IV) oxide, consisting of metal ions having smaller ionic potential, were amphoteric ion exchangers possessing large anion-exchange capacities, and showed much higher affinity for the transition metal ions than for the representative element ions. The selectivity series are understood in terms of the formation of a bond partially covalent in character for the transition metals, and the purely electrostatic interaction between anionic exchange sites and unhydrated or hydrated cations for the representative elements. An examination of ...

Two-Phase Flow Pattern .and Heat Transfer during Core Uncovery

Abstract: The low and high power core uncovery patterns were observed in the high-pressure quasi-steady core uncovery experiments in a 25-rod bundle. The boundary between the two patterns was obtained in the experiments. The difference of two patterns was considered to be due to the slug-annular transition below the dryout points. The Osakabe's slug-annular transition model was the good boundary between the two patterns. The small break loss-of-coolant accident (LOCA) experiments were conducted by using the integral experimental facility with the 1,168-rod core. The transient core uncovery pattern was expected as the low power core uncovery pattern based on the quasi-steady experiments mentioned above. The transient core uncovery patterns were classified into the boiloff and hydraulic core uncovery. In the boiloff core uncovery, the dryout points were controlled with the mixture level like the quasi-steady state. In the hydraulic core uncovery, the dryout points were not controlled with the mixture level alone, and...