Transformation and fragmentation behavior of molten metal drop in sodium pool

In order to clarify the fragmentation mechanism of a metallic alloy (U–Pu–Zr) fuel on liquid phase formed by metallurgical reactions (liquefaction temperature = 650 °C), which is important in evaluating the sequence of core disruptive accidents for metallic fuel fast reactors, a series of experiments was carried out using molten aluminum (melting point = 660 °C) and sodium mainly under the condition that the boiling of sodium does not occur. When the instantaneous contact interface temperature (T_i) between molten aluminum drop and sodium is lower than the boiling point of sodium (T_c,bp), the molten aluminum drop can be fragmented and the mass median diameter (D_m) of aluminum fragments becomes small with increasing T_i. When T_i is roughly equivalent to or higher than T_c,bp, the fragmentation of aluminum drop is promoted by thermal interaction caused by the boiling of sodium on the surface of the drop. Furthermore, even under the condition that the boiling of sodium does not occur and the solid crust is formed on the surface of the drop, it is confirmed from an analytical evaluation that the thermal fragmentation of molten aluminum drop with solid crust has a potential to be caused by the transient pressurization within the melt confined by the crust. These results indicate the possibility that the metallic alloy fuel on liquid phase formed by the metallurgical reactions can be fragmented without occurring the boiling of sodium on the surface of the melt.     

Prospects of using different clad materials in a material test research reactor – Part 1 – The kinetic parameters

The kinetic parameters of a material test research reactor using stainless steel-316 and zircaloy-4 as clad were calculated. For this purpose, the aluminum clad of an MTR was replaced separately with stainless steel-316 and zircaloy-4. Calculations were carried out to find the core excess reactivity, neutron flux spectrum, prompt neutron generation time and effective delayed-neutron fraction. Nuclear reactor analysis codes including WIMS-D4 and CITATION were employed to carry out these calculations. It was observed that at the beginning of life, the excess reactivity was maximum at 0.054110 Δk/k when zircaloy-4 was used as clad while it was minimum at ?0.365650 Δk/k when stainless steel-316 was the clad as compared to 0.017945 Δk/k for aluminum. The thermal neutron flux at the mid of the central flux trap increased by 59.9% and 12.5% for stainless steel and zircaloy-4 clads, respectively, from the flux of the original aluminum clad. The prompt neutron generation time was maximum at 45.36 μs when stainless steel-316 was the clad while it was minimum at 44.03 μs for the original aluminum clad. The effective delayed-neutron fraction was maximum at 0.007185 for the original aluminum clad while it was minimum at 0.007078 for stainless steel clad.     

Extraction of Lithium from Sea Water with Metallic Aluminum

Extraction of lithium from sea water was investigated. It was found that a corrosion product of metallic aluminum immersed in sea water extracts lithium from it selectively. Effects of the temperature and the pH of sea water, and of the initial concentration of lithium in it were examined. On the basis of the analysis of the surface deposit on aluminum, which is a corrosion product of aluminum, the selectivity coefficients were calculated. For the extraction of lithium from natural sea water, the values of K ^Li _Na ^Li _MgK ^Li _Ca and ^Li _K were 9.9 × 10², 1.1×10, 4.5×10 and 4.4 × 10², respectively.     

Synthesis,characterization and solubility of mixed zirconium-cerium molybdate precipitates

The reaction between fission products Mo(VI) and Zr(IV) in hot nitric acid solution during the spent fuel dissolution process leads to the formation of hydrated zirconium molybdate precipitate. This solid can include other metallic cations at the 4th oxidation state (+ IV) inside the crystal such as Pu(IV).

Precipitations in the inactive surrogate system of mixed zirconium-cerium molybdates Mo-Zr(IV)-Ce(IV) were performed all over the cerium molar percentage scale from 0 to 100%, Ce(IV) being used as a surrogate of Pu(IV). The crystal structures were identified from powder X-ray diffraction patterns and complementary investigations by SEM and elemental analyses were carried out. The solid composition pointed out two phases that are ZrMo₂O₇(OH)₂(H₂O)₂ and Ce₃Mo₆O₂₄(H₂O)₄. Each of these compounds was proved being a solid solution within which the Zr^IV and Ce^IV atoms can substitute each other.

Moreover, the influence of the cerium molar fraction on the precipitate solubility was investigated and showed a strong evolution of solubility not only with the nature of the precipitate and the Ce content, but also with the nitric acid concentration.     

Description of Aerosol Release Associated with Sodium Burning

Incipient temperatures of sodium oxidation, sodium oxide aerosol release and sodium ignition were observed in relation with oxygen concentration in supplying gas by a thermobalance method. On this results, a burning rate and an aerosol release fraction were determined by burning about 0.5 g of sodium samples on a crucible in a burn tube under conditions ranging 400 to 600°C in sodium temperature, 0.1 to 1.0 Nl/min in the supplying gas flow rate and 2.5 to 20v/0 in the oxygen concentration.

Particle sizes of sodium aerosols released from the samples made a log-normal distribution, of which mass median diameter ranged from 0.6 to 2.0 μm. The burning rate increased with the increases of the sodium temperature, of the gas flow rate and of the oxygen concentration, and the aerosol release fraction also increased in proportion to the burning rate at fixed oxygen concentrations. It was found that the aerosol release rate defined as a product of the burning rate and the aerosol release fraction describes fairly well not only the present experimental data but also reported ones.     

Comparative analysis of the low-energy He+ ions scattering on Al and Al2O3 surfaces

Using the Anderson–Muda–Newns approach, the neutralization rate and the ion survival probability have been calculated for the large angle scattering of low-energy He⁺ ions by Al and by Al₂O₃. The two-band model of the electronic energy spectra is applied for the case of alumina. The electron promotion has been shown to play an important role in the processes of the He⁺ ions scattering by aluminum and alumina. The experimentally observed absence of the matrix effect is discussed on the basis of the obtained results.     

The solubility of deuterium in lithium-lead alloys

The solubility of deuterium in lithium-lead alloys was measured as a function of temperature and atomic fraction of lithium, X_Li. It was found that, at the atom fraction X_Li = 0.78, corresponding to the composition “Li₇Pb₂”, the solubility in the solid phase is lower by a factor of a few hundred than that in the liquid phase. The solubility of deuterium in the Li-Pb system decreases drastically with decreasing X_Li. At about X_{Li = 0.17}, which corresponds to the eutectic “Li₁₇Pb₈₃”, the solubility is independent of temperature. The transition from exothermal to endothermal dissolution occurred at about X_Li ? 0.17.     

Incipient Boiling of Sodium in an Annular Channel Heated by a Single-Pin with Blockage

Abstract

In simulation of partial failure affecting a fast breeder core, experiments on sodium boiling were performed in a single vertical channel of annular cross section (15 mm I.D.), indirectly heated by high flux heater pin (6.5 mm O.D., 60 cm heating length) and provided with a blockage disk (11mm O.D., 1mm thick, obstructing 42% of the channel area). The experimental conditions were; Pressure of cover gas: 1.0 kg/cm² abs., Heat flux: 0–80 W/cm², Flow rate of sodium: 1–4/l min.

The results revealed that the degree of incipient boiling superheat is reduced to a fraction of the value obtained previously for direct joule heating under similar conditions, and that, consequently, the intensity of pressure pulses is correspondingly reduced. On the other hand, the incipient boiling superheat increases, together with the extent of its scattering, with rising intensity of the heat flux.

Local boiling was observed to precede the onset of bulk boiling, causing small pressure spikes to be detected by all three pressure sensors installed along the test channel. The pressures evaluated from the measured velocities of the liquid sodium column based on single-bubble model were compared with the measured pressure signals, and a fairly good agreement was obtained.     

Composition and structure of fission product precipitates in irradiated oxide fuels: Correlation with phase studies in the Mo-Ru-Rh-Pd and BaO-UO2-ZrO2-MoO2 Systems

Composition and crystal structure of fission product precipitates in irradiated oxide fuels were studied by X-ray microanalysis and X-ray diffraction using instruments shielded for α-contamination and β-γ-radiation. Pin cross-sections, fuel micro-samples from 300 μm hollow drillings and residues from the dissolution of irradiated material in HNO₃ were investigated. The metallic phases found are hcp ?-Ru(Mo,Tc,Rh,Pd) solid solutions with broad variations in concentration of the components, bcc β-Mo(Tc,Ru) and fcc α-Pd(Ru,Rh). The dominating ceramic precipitate is composed of ($\text{Ba}{}_{\mathrm{1-x-y}}\text{Sr}{}_{\mathrm{x}}\text{Cs}{}_{\mathrm{y}}$)(U,Pu,RE,Zr,Mo)O₃ which crystallizes in the cubic perovskite type. The Mo fraction of these phases is related to the local oxygen potential of the fuels. The in-pile observed results agree well with phase studies in the quaternary Mo-Ru-Rh-Pd system where complete solid solubility exists between hcp Ru and the hexagonally stabilized Mo-Rh and Mo-Pd phases. Agreement is further attained with phase studies in the pseudoquaternary BaO-UO₂-ZrO₂-MoO₂ system which is characterized by a cubic perovskite phase Ba(U,Zr,Mo)O₃.     

Improvement of reactivity coefficients of metallic fuel LMFBR by adding moderating material

For a metallic fuel liquid metal fast breeder reactor, we studied a core concept for improving the Doppler coefficient and the sodium void reactivity without much sacrificing the breeding ratio and the burnup reactivity loss. In the concept, several ordinary fuel pins in all fuel assemblies of a core are substituted by pins containing only zirconium hydride (ZrH). A parametric survey for the ZrH fraction from about 1 to about 5% was performed in this study to investigate the reactivity coefficients and the associated demerits in order to search the optimum fraction of ZrH. The metallic fuel core containing about 3% of ZrH showed the good results for all parameters. Following the parametric study, the effect of hydrogenous material in a metallic fuel core was experimentally confirmed. Doppler reactivity, sodium void reactivity and sample reactivity worths of plutonium and B₄C were measured in a series of critical experiment at FCA of JAERI. The experimental results showed that the hydrogenous material significantly improved the Doppler and the sodium void reactivities. Analysis of experimental results was performed to check the applicability of the present design codes for a fast reactor with hydrogenous materials.     

Effect of LiNO3 on Corrosion Prevention of Aluminum Wastes after Their Land Disposal

After their land disposal, LiNO₃ added to cement solidified miscellaneous wastes inhibits hydrogen gas generation due to alkaline corrosion of aluminum contained in the wastes. We considered the presence of an Li-Al preservation film prevents hydrogen gas generation, and then, we assumed a scenario in which the amount of LiNO₃ included in the waste packages is lowered by underground water penetration, resulting in dissolution of the Li-Al preservation film. This dissolution allows the alkaline underground water to reach and corrode the aluminum materials. The loss of Na₂O and K₂O in cement by underground water penetration lowers the pH, so that the aluminum corrosion in the waste packages with LiNO₃, expected when the Li-Al preservation film dissolves, is less than that without LiNO₃.

To test this scenario, we measured solubility of the Li-Al preservation film, Li⁺ ion concentration, pH variation by underground water penetration, and aluminum corrosion when the Li-Al preservation film had dissolved. The measured solubility of the Li-Al preservation film was 3 × 10^?4 _M at 283 K. At that time, pH was lowered from 12.9—13.0 to 12.2—12.3. As a result, with LiNO₃ addition the aluminum corrosion amount was reduced to 10% of that without LiNO₃ addition, because of the pH decrease.     

Evaluation of precipitates used in strainer head loss testing: Part II. Precipitates by in situ aluminum alloy corrosion

Vertical loop head loss tests were performed with 6061 and 1100 aluminum (Al) alloy plates immersed in borated solution at pH = 9.3 at room temperature and 60 °C. The results suggest that the potential for corrosion of an Al alloy to result in increased head loss across a glass fiber bed may depend on its microstructure, i.e., the size distribution and number density of intermetallic particles that are present in Al matrix and FeSiAl ternary compounds, as well as its Al release rate. Per unit mass of Al removed from solution, the WCAP-16530 aluminum hydroxide (Al(OH)₃) surrogate was more effective in increasing head loss than the Al(OH)₃ precipitates formed in situ by corrosion of Al alloy. However, in choosing a representative amount of surrogate for plant specific testing, consideration should be given to the potential for additional head losses due to intermetallic particles and the apparent reduction in the effective solubility of Al(OH)₃ when intermetallic particles are present.     

Carbonate Complexation of Np(VI) in Near-Neutral Solutions

Abstract

A spectroscopic study of Np(VI) was performed in carbonate solutions. The characteristic absorption bands were observed at 625, 670 and 703 nm and examined for the dependence on pH and carbonate concentration. The absorbances showed no dependence on pH but proportionally increased with the increasing carbonate concentration. From the observations, the result was analyzed by considering the reaction of NpO₂(OH)2_(s)+CO₃ ^2-=NpO₂ (OH)₂CO₃ ^2-. By measuring the solubility, the equilibrium reaction constant was calculated to be log K=- 2.49±0.15. The stability constant of NpO₂(OH)₂CO₂ ^2- was predicted to be log β= 20.21±0.15 by taking the literature value of solubility product of NpO₂ (OH) _2(s).     

Liquid Metal Extraction for Removal of Molybdenum from Molten Glass Containing Simulated Nuclear Waste Elements

Laboratory-scale experiments for removing Mo and MoO3 from molten borosilicate glass were performed using liquid Cu as an extractant. Removal of Mo from the simulated HLW glass containing oxides of Nd, Fe, Zr, Mo, Sn, Ni, Sr, Cd, Ru, and Se was also performed, and the fractions of these elements transferred into Cu were examined. Mixtures of Cu anda ternary SiO₂-B₂O₃-Na₂O glass containing metallic Mo or MoO₃ were heated in an alumina crucible at 1,673K in an Ar environment. The amounts of Mo and MoO₃ added to 10 g of the ternary glass were fixed at 0.1 and 0.15 g, respectively. As for the glass containing metallic Mo, more than 90% of Mo was extracted into liquid Cu. Spherical Cu metal buttons containing Mo formed on the bottom of the crucible when Cu was added at more than 10 times that of Mo on a mass basis. Removal of Mo from the glass containing MoO3 was also achieved by the addition of Si as a reducing agent for the reduction from MoO₃ to Mo. The fraction of Mo extracted into liquid Cu depended on the molar ratio of Si to Cu added to the glass. The fraction increased up to 84% with an increase in the molar ratio of Si/Cu. However, the excess addition of Si may enhance the chemical interaction between the metal phase and the glass phase, and some of the metal phase containing Mo remained in the glass phase without forming a metal button. The optimum molar ratio of Si/Cu that produces the highest removal fraction was found to be approximately 0.5. Almost the same removal fraction of 88% was obtained from the simulated HLW glass under the condition of Si/Cu = 0.5. Nearly 100% of Ru was extracted into Cu with Mo, while Sr, Zr, and Nd were hardly extracted and remained in the glass.     

Deposition of Alumina Films on Si (1 0 0) Substrate Using a Low Energy Dense Plasma Focus Device

A 1.5 kJ pulsed low energy Mather type plasma focus (PF) is used to deposit thin films of alumina (α-Al₂O₃) on Si (1 0 0) substrates. The PF device with its anode made of aluminum was operated with argon-oxygen mixture as the filling gas. The Al₂O₃ thin film samples were prepared using 10, 20 and 30 successive shots with substrates placed at 60 mm from the top of the anode at approximately zero angular position with respect to the anode axis. The crystallography of the as-deposited and annealed samples was studied by X-ray diffractometry (XRD). Raman Spectroscopy studies verified the formation of α-Al₂O₃ phase in the annealed films. Scanning electron micrographs (SEM) of the annealed films present many different sized particulates (50–300 nm) distributed upon the film surface. The cross-sectional SEM micrographs show that the thickness of deposited alumina film is linear with a typical rate of 45 nm/shot at focus storage energy of 850 J.     

Effects of different surfaces on the transport and deposition of ruthenium oxides in high temperature air

In order to understand the behaviour of ruthenium oxides in the reactor coolant system during an air ingress accident, new tests were performed in the frame of the RUSET (RUthenium Separate Effect Test) experimental program. These aimed to ascertain the effects of different surfaces (quartz, stainless steel (SS), zirconium alloy, alumina, oxidised metal, and surfaces with Mo or Cs deposits) on the transport and decomposition of ruthenium oxides in air stream along the temperature gradient zone (1100–100 °C). The results demonstrated that the heterogeneous phase decomposition of RuO₃ and RuO₄ to RuO₂ is catalysed more efficiently by the quartz surface than by the SS or alumina surfaces. The presence of MoO₃ layers decreased the RuO_x precipitation extent on all investigated surfaces. The trapping effect of Cs deposit on Ru in the temperature gradient zone was proved in the case of the SS surface. On the contrary, presence of Cs precipitate on alumina and especially on quartz surfaces was found to decrease their catalytic effect on the decomposition of ruthenium oxides, and thus increased the RuO₄ concentration in the outlet air. Similarly to the effect observed for Cs deposition, the presence of other fission products in the evaporation area (at 1100 °C) decreased the partial pressure of RuO₄ in the outlet air at the SS surface and increased it at quartz and alumina surfaces. When zirconium (E110) cladding material was placed in the temperature gradient zone, no Ru transmittance occurred until the high temperature end of the zirconium tube was completely oxidised. After the intense oxidation of E110, Ru release occurred only in the presence of other fission product species. Pre-oxidation of SS surfaces in steam had no significant effect on the Ru passage.     

Solubility of Tributylphosphate in Plutonium Nitrate Solution and Highly Radioactive Liquid Waste Solution

Abstract

The solubility of tri-n-butylphosphate (TBP) in aqueous solutions of plutonium nitrate (PuN) and in highly radioactive liquid waste (HRLW) of PUREX nuclear fuel reprocessing was investigated. By an empirical formula the solubility of TBP in PuN solutions was described in the range of 0–0. 1 M Pu and 1–8M HNO₃ concentrations. The following items were elucidated:

(1) The logarithm of TBP solubility (S) in the solution of interest varies inversely in proportion to the concentration of Pu(IV) in the range of 0–0.1M PU(IV) at a constant concentration of HNO₃, indicating that Pu(IV) simply behaves as an electrolyte for the salting-out of TBP. Log S subsequently levels off with increasing Pu concentration, which would be due to a change in the principal dissolution form of TBP having an interaction with Pu (IV).

(2) The variation in S in PuN solutions (0–0.1M PU) with nitric acid concentration shows almost the same tendency as that in HNO₃ solution.

(3) A dependency of S on fission product metal ions in HNO₃ for HRLW similar to that for PuN was observed.

(4) The logarithm of the ratio of TBP solubility in water to that in solution of interest was nearly proportional to l/T for HRLW solution or for low concentration of PuN solution. That deviates from the linear relation at high temperature when the concentration of PuN is increased, which can be explained by the change in ionic form of Pu.     

Local Gamma-Ray Counting Efficiency of Halogen Counter with Thick Anode

A substance for solidifying waste containing ¹²⁹I is sought that effectively sorbs iodine to inhibit its release from repository into the environment. Three candidate media—commercial alumina cement mixed with calcium sulfate and/or calcium hydroxide—were investigated. The criterion applied for evaluating iodine sorption performance was the distribution coefficient Kd of iodine between solid and solution in an emulsion of sodium iodide solution and powder prepared from the alumina cement/calcium compound mixture, which was molded, cured and ground. Batch sorption experiments were performed on different combinations of the above-mentioned calcium compounds added to alumina cement. The solidified substance was also examined for mechanical strength. The highest iodine sorption performance was obtained with calcium sulfate added to alumina cement to a SC₄/Ca mole ratio of 0.16, which ensured a Kd value raised to a level of not lower than 0.2 m³/kg from the (1.8–3.2)x10^-3 m³/kg obtainable with alumina cement before calcium compound addition. The enhancement of iodine sorption with addition of calcium sulfate is attributed to formation in the substance of monosulfate (3CaO·Al₂O₃·CaSO₄12H₂O) or tetracalcium aluminate hydrate (4CaO·Al₂O3·XH₂O (X=13 to 19)).     

Reactive Wetting of Metallic Plated Steels by Liquid Sodium

Sodium wetting experiments were performed to investigate the reactive wetting of metallic plating materials by liquid sodium at 250°C for the ultrasonic sensor of the under-sodium viewer. SUS304 stainless steel specimens were electrolytically plated with four metallic materials (nickel, palladium, gold, and indium) that have different solubilities in sodium, and the spreading velocity of sodium droplets on the metallic plated specimens was measured. It was confirmed that the spreading velocity increased as the solubility increased, and the constant α on the spreading velocity on the plated specimens was unique for the plating materials and was proportional to the logarithm of the solubility of the plating materials. Furthermore, it is considered possible to select plating materials based on solubility from the result of this study.     

Radiolytic Oxidation Behavior of Neptunium in Sodium Chloride Solutions

Radiolytic oxidation behavior of neptunium was investigated in order to predict its migration behavior at the disposal site for radioactive waste. Neptunium, in 5 mol/dm³ sodium chloride solutions of several pH values, was irradiated by α-particles of ²³⁸Pu which had been placed in the solutions as dioxide powder. Solution neptunium redox behavior was compared with that of an unirradiated sample. Pentavalent neptunium, which was stable in the absence of ²³⁸Pu, was found to be oxidized to hexavalent and even to heptavalent neptunium. Oxidizing species would be chloride molecule anion (Cl^? ₂) and/or hypochlorite anion (ClO^?) which were generated by the reaction between radiolytically generated hydroxide radical (OH) and chloride ion (Cl^?). The oxidation rate of pentavalent neptunium was independent of its concentration, but dependent on solution pH. The measured rate constant was (19±4)[H] mol/dm³/d.