C. Mallika

New Data on Activity Coefficients of Potassium, Nitrate, and Chloride Ions in Aqueous Solutions of KNO 3 and KCl by Ion Selective Electrodes

Ion selective electrodes (ISEs) are used to measure the single-ion activity coefficients in aqueous solutions of KNO3 and KCl at 298.15K against a double-junction reference electrode. The EMF responses of ISEs up to 0.01m are plotted to obtain the slope and intercept values. The obtained slopes and intercepts are used in Nernst equation for higher concentrated solutions for calculation of individual ion activity coefficient. The mean ionic activity coefficients are estimated from single ion activity coefficient, and the obtained results are compared with the literature values.

Destruction of soluble organics generated during the dissolution of sintered uranium carbide by mediated electrochemical oxidation process

Abstract The destruction of soluble carbonaceous compounds formed during the dissolution of sintered uranium mono carbide pellets in 11.5 M nitric acid at 65 °C has been investigated by employing mediated electrochemical oxidation (MEO) method, in which process 0.05 and 0.01 M Ag(II) and 0.1 and 0.06 M Ce(IV) were used as the regenerable catalysts. The current density and temperature of the process for maximum destruction efficiency were optimized to be 25 mA/cm2 and 75 °C respectively. The electro-oxidation behaviour of the mediator ions Ag(II) and Ce(IV) with respect to their concentration in the removal of organics and the dependence of temperature on the stabilities of the two electrochemical catalysts were compared. The effect of fission product elements in a synthetic dissolver solution on the performance of Ag(II) mediator in oxidizing the carbon content was discussed. The destruction efficiency of MEO process in eliminating the soluble organics was ascertained to be better than that of direct electrochemical oxidation method as well as prolonged oxidation of the organics with concentrated nitric acid.

Corrosion Behavior of Structural Materials in LiCl-KCl Molten Salt by Thermogravimetric Study

Spent metallic fuel from future fast-breeder reactors would be processed by non-aqueous pyrochemical reprocessing. Different unit operations of pyrochemical reprocessing demands various structural materials that are compatible with molten salt medium at high temperatures. In the present study, the corrosion behavior of the candidate materials stainless steel (SS) 410, alloy 600 and 9Cr-1Mo (9% chromium and 1% molybdenum) steel was investigated in molten lithium chloride–potassium chloride (LiCl-KCl) salt by thermogravimetric studies under inert and reactive atmospheres. The test specimens, along with molten salt, were isothermally heated at 500 and 600°C for 24 h in both atmospheres. Alloy 600 showed marginally higher weight gain than 9Cr-1Mo and SS410 under both atmospheres at 600°C. Higher weight gain was observed under reactive atmosphere than in inert atmosphere at 600°C. All of the samples investigated under both atmospheres at 500°C showed insignificant weight loss. The surface morphology and energy...

Corrosion Behavior of Zirconium, Titanium, and Their Alloys in Simulated Dissolver Solution of Fast Breeder Reactor Spent Nuclear Fuel Using Zircaloy-4 Mock-Up Dissolver Vessel

Abstract Long-term corrosion testing of a mock-up dissolver vessel to be employed in the aqueous reprocessing of spent nuclear fuels of fast breeder reactors has been initiated. In this work, a Zircaloy-4 (Zr-4) mock-up dissolver vessel was used as the testing facility to evaluate the corrosion rate of several candidate materials based on zirconium and titanium in the boiling and vapor phases of simulated dissolver solution (SDS) comprising fission and corrosion product ions in 11.5 M nitric acid. Several campaigns of 100, 250, 500, 1000, and 2500 h of operation were completed. The corrosion rates of the candidate materials are expressed both in micrometers per year (μm/yr) and mils per year (mils/yr). Zirconium-702, Zr-4, autoclaved Zr-4, and commercial pure titanium (CP-Ti) exhibited low corrosion rates of 0.08 to 0.23 μm/yr (0.003 to 0.009 mils/yr) in the as-received and welded conditions exposed to the boiling liquid phase of the dissolver solution for 2500 h. Whereas the CP-Ti and CP-Ti weld exhibited marginally higher corrosion rates of 1.0 μm/yr (0.04 mils/yr) and 1.9 μm/yr (0.075 mils/yr), respectively, in the vapor phase of the dissolver solution, the lowest corrosion rate of 0.08 μm/yr (0.003 mils/yr) was obtained for the autoclaved Zr-4 sample exposed to boiling SDS. Scanning electron microscope investigations did not reveal any corrosion attack for the titanium and zirconium samples. Laser Raman spectroscopic analysis confirmed that the origins of passivity of zirconium and titanium samples were due to the formation of ZrO2 and TiO2, respectively. However, the CP-Ti/AISI Type 304L stainless steel (SS 304L) and Zr-4/SS 304L dissimilar welds had undergone severe corrosion. Visual inspection of the Zr-4 dissolver vessel revealed no corrosion attack after operation for 2500 h. The results of this 2500-h campaign would serve as the baseline data for the analysis of future long-term campaigns.

Effect of Laser Surface Melting on the Microstructure and Pitting Corrosion Resistance of 304L SS Weldment

The manuscript presents the effect of laser surface melting (LSM) on the microstructural variations and pitting corrosion resistance of 304L SS weldment fabricated by gas tungsten arc welding of 304L SS plates using 308L SS filler wire. The weld region was examined by X-ray radiography for defect detection. LSM of 304L SS weldment was performed using Nd:YAG pulsed laser. Microstructural evaluation was carried out using optical and electron back scatter diffraction techniques. The microstructure of 304L SS base was found to be austenitic, while the weld region of 304L SS weldment contained delta ferrite distributed in austenite matrix. The microstructure of LSM 304L SS weldment was found to be homogeneous austenite matrix with sparsely distributed ferrite. Ferrite measurements showed a decrease in the percentage ferrite in the fusion zone of 304L SS weldment after LSM. A profound enhancement in the pitting corrosion resistance was observed after LSM, which could be attributed to the homogeneous microstructure and decrease in the ferrite content. Pit density was found to be higher in the heat-affected zone of the weldment. Very few pits were observed in the LSM 304L SS weldment compared to the as-weldment.

Aluminum phosphate sealing to improve insulation resistance of plasma-sprayed alumina coating

ABSTRACT The insulation resistance of conventional atmospheric plasma-sprayed alumina coatings with 10–15% porosity is ∼1011 Ω. The presence of pores, lamellae boundaries, and other non-fillings dampens the insulation resistance of the coating. In the present study, aluminum phosphate was used to seal the surface of plasma-sprayed alumina coating and evaluate the effect of sealing on the insulation resistance and its thermal cycling response. Sealing was carried out with three concentrations of sealant (P/Al molar ratio of 3, 10, and 15). Characterization by X-ray diffraction and scanning electron microscopy revealed the primary sealing phase as aluminum metaphosphate and effective sealing of the pores by the aluminum phosphate phases. Insulation resistance is improved by two orders of magnitude after sealing the coated samples. Sealing with P/Al molar ratio 3 exhibited maximum insulation resistance of ∼1013 Ω at room temperature. Thermal cycling studies between 650°C and 200°C on the sealed samples showed deterioration in thermal cycling life after sealing.

Evolution in physiochemical properties of alternate PUREX solvent on hydrolytic and chemical treatment

ABSTRACT Physiochemical properties such as density, viscosity, interfacial tension (IFT) and phase disengagement time (PDT) were measured after subjecting tri-iso-amyl phosphate (TiAP)-based solvent systems to hydrolytic treatment at 40 and 50°C, for 400 h. The change in viscosity between the degraded and fresh solvent was significant compared with the change in density, which could be due to the formation of intermediate compounds susceptible to hydrogen bonding. The marginal variation in the IFT values even after accelerated treatment and the absence of any new class of compounds after treatment, as evidenced by FTIR spectral analysis, revealed that the solvent exhibited good thermal and chemical stability.

Corrosion behaviour of 304LN activated tungsten inert gas and flux-cored arc weld metals

Activated tungsten inert gas (A-TIG) and flux-cored arc (FCA) weld metals were prepared using 304LN stainless steel plate. The weld metals were thermally aged at 923, 973 and 1023 K for 100 h to study the decomposition of initial δ-ferrite in A-TIG (∼10 ferrite number (FN)) and FCA (∼5 FN) weld metals into secondary phases like M23C6 carbides, χ and σ. Ferrite number is the measurement of δ-ferrite based on the principle of magnetic property using ferritescope. Preliminary microstructural studies revealed the formation of carbides in FCA weld metals aged at 923 K for 100 h, which was correlated with higher carbon content (0.04 wt-%), and also ageing at higher temperature transformed δ-ferrite into χ/σ phases. However, A-TIG weld metals showed the transformation of δ-ferrite mainly into χ/σ phases. The δ-ferrite transformation kinetics was found to be sluggish in A-TIG weld metals compared to FCA weld metals. This difference was attributed to the difference in the carbon contents of A-TIG and FCA welds. Activated tungsten inert gas weld metals showed better uniform and pitting corrosion resistance compared to FCA weld metals in as-deposited and thermally aged conditions. Presence of higher amount of initial δ-ferrite content in A-TIG weld metal helped diffusion of minor alloying elements like sulphur and phosphorous into it, thereby reducing their microsegregation at the δ/γ interface boundaries and subsequent pitting corrosion attack. Thus, A-TIG welding process was found to be superior compared to FCA welding process.

Plasma-sprayed alumina coating on Inconel 600 for fast reactor neutron detector application

ABSTRACT Alumina coating, with high electrical resistivity, has been proposed over Inconel 600 rings for application in fission chamber neutron detectors, operating at 923 K in fast breeder reactor. For improving the thermal cycling life and adhesion strength of alumina coating, selection of the suitable coating technique and bond coat, with appropriate spray parameters was pursued. In the present study, Ni–50%Cr bond coat was deposited over Inconel 600 by the high velocity oxygen fuel technique, while the top alumina coat was deposited using air plasma spray process. A dense coating with minimum porosity and a stable insulation resistance (600 V DC) of ∼1011 ohm at room temperature and ∼108 ohm at 923 K was achieved. Thermal cycling studies on coated samples and rings showed good thermal cycle life tested up to 100 cycles. The coating exhibited good bond strength and only marginal decrease in bond strength was observed with increase in thermal cycling.

Feasibility studies of using N,N-dihexyloctanamide (DHOA) for fast reactor fuel reprocessing applications

Abstract N,N-dihexyloctanamide (DHOA) is being considered as a promising extractant in the aqueous reprocessing of spent nuclear fuels. In view of rise in temperature of the solvent during reprocessing of fast reactor fuel, the present study aimed at evaluating the physical properties such as density, viscosity, and interfacial tension and Pu(IV) extraction behavior in 1.1 M DHOA/n-dodecane as a function of temperature and duration of heating. The influence of nitric acid in altering the physical properties with respect to temperature was evaluated. Physical properties and extraction behavior of the solvent changed to a remarkable extent with temperature. Quantitative amount of Pu(IV) could be back-extracted from loaded, solvent in three contacts at 313 K. FT-IR studies were carried out to evaluate the thermal stability of the solvent. Thus, the performance of the solvent, 1.1 M DHOA/n-dodecane is satisfactory at higher temperatures also.