[en] India has designed its three-stage nuclear power program based on domestic limited resources of uranium and vast availability of thorium, where natural and enriched uranium-dioxide fuel is utilized in Pressurized Heavy Water Reactors (PHWR) and Boiling Water Reactors (BWR) respectively in the first stage. Plutonium based fuels are implemented for Fast Breeder Reactors (FBR) in the second stage and thorium based fuels are to be utilized using indigenously developed reactors in the third stage. Considering the harsh reactor operating conditions like high temperature and pressure and neutron flux, in-core components used in the above reactors are to be manufactured with different critical materials like Zirconium alloys, Special SS materials, ODS etc. Welding the best joining technique used for joining in-core components, and can perform satisfactorily in the reactors. The welding processes used in nuclear applications have to conform to stringent quality requirements to achieve zero failures rate. In view of the stringent weld quality requirements and amenable for automation various weld joint designs and welding processes were selected for fabrication of in-core components such as Resistance Welding, Tungsten Inert Gas welding and Electron Beam Welding. In this paper, overview is given for all the major welding processes used and its specific applications for fabrication of in-core components used in nuclear reactors. The welding process intricacies are explained and weld quality evaluation techniques are briefly brought out. The joint design modifications and improvements achieved with respect to welding operations over decades of reactor operating experiences are also explained, which helped in reducing fuel and in-core structural components failures for Indian nuclear reactors. (author)

[en] Superconducting high purity niobium is important for particle accelerators in a variety of applications. Critical to the performance of superconducting accelerator devices is the quality of industrially produced niobium sheet, both in terms of low interstitial content as well as freedom from harmful chemical inclusions. At the present time Nb is the only superconductor metal of the second kind with higher critical magnetic field, reasonably high critical temperature Tc and Residual Resistance Ratio, good thermal conductivity and formability, hence of practical importance in the field of super conductivity. Three niobium-based materials make up the entire present portfolio of superconducting technology for accelerators: pure Nb metal, Nb-Ti and Nb₃Sn. This article covers details of the process developed at NFC for production of Nb sheets through multiple EB Refining of thermit–Extrusion– Rolling etc covering specific achievements, practical aspects and technological challenges in production and characterization. Achievement of the full potential of r.f. superconductivity is closely tied to further advances in Nb quality. Efforts are being put to fine tune the process parameters towards advances in quality

[en] Finite element simulation of nuclear fuel element end cap solid state resistance upset welding process is attempted using dedicated resistance welding FE simulation package SORPAS. Basic two-dimensional axsymmetric modeling has been done with temperature dependent electrical, thermal and structural properties for Zircaloy-4. The simulation results of weld bead shape and weld upset are compared with experimental values with same welding parameters. It is observed that simulation package SORPAS is very useful for modeling bulk deformation process such as end cap welding. Using the developed two-dimensional model, the simulation results are obtained with varying pre-heat and post-heat welding current, pre-heat and post-heat cycle duration. The observations are validated using experimental results with same range of varying welding parameter values. However, better modeling and analysis of complicated end cap resistance upset welding is possible in future by simulating real welding environments using SORPAS and suitable experimental arrangements

[en] The performance PHWR fuel bundle depends on the quality of resistance weld joints and individual components of the bundle. Stringent quality inspection techniques are followed, which includes visual and dimensional inspection of all resistance welds and bundle components to avoid defective components being converted to final bundle form in production stream. An automatic vision based tube inspection system is now being introduced at NFC, which identifies and separates acceptable and defective fuel tubes by carrying out multiple quality checks on a single unit. The details of the inspection system, its reliability and advantages are described in this paper. (author)

[en] The inter element spacing in Pressurized Heavy Water Reactor (PHWR) fuel elements is maintained using small tiny components, known as spacer pads, to avoid any hot-spot formation due to surface to surface contact of fuel elements in reactor operating conditions. The bearing pads are welded to the outer elements of fuel bundle to provide support to it in the coolant channel. The spacer and bearing pads, made of Zircaloy-4 material, are collectively known as appendages. Indigenous capabilities for joining these appendages to empty Zircaloy-4 fuel tubes were developed by Nuclear Fuel Complex (NFC) for large scale regular mass production of nuclear fuel bundles for reactors operating all over India. The welding process is well established and standardized in various aspects for industrial scale automation and consistent quality over the last few decades at NFC. However, systematic analysis of this unique welding process is limited in literature. In this paper, an attempt is made to analyze the resistance projection welding process of appendages to fuel tube using coupled finite element analysis for studying the peak temperature, extent of joining area at the interface, projection and diametrical tube collapse and the extent of heat affected zone during the process. A two-dimensional simplified ax-symmetric model is developed to study the welding process and the simulated results are validated using experiments performed with dedicated data acquisition system for resistance welding. The study is further extended for calculating shear strength of the weld joints, which is frequently used as destructive weld quality evaluation test. The study will be helpful in prediction of weld quality for different variations in input welding parameters to avoid weld failures during regular large scale production

[en] The temperature distribution in solid-state end cap welding process is predicted using analytical heat transfer study and the results are verified using thermal imaging technique. The predicted and actual temperature rise with welding time showed similar trends. The temperature rise occurs at much faster rate in the initial phase due to high initial contact resistance between cladding tube and end cap. The peak temperature in the welding process for the current ranges of welding variables reaches around 850°C-900°C under normal operating conditions, which supports the presence of Widmanstaetten or martensitic structures at the heat affected zones in end cap welding. However, more accurate measurements of the temperature are possible in future with the use of photo-sensors with very low response time. (author)

[en] The Pressurized Heavy Water Reactor uses fuel in the form of natural UO₂ pellets, produced by powder metallurgy route from sinterable grade UO₂ powder. Ex-AU route is widely accepted process for production of highly sinterable grade UO₂ powder. The characterization of UO₂ powder is always paramount for final pellet recovery. Sinterability of UO₂ powder largely depends on precipitation and subsequent heat operation namely calcination and reduction. Ammonia flow rates during AU precipitation and temperature of calcination and reduction are critical to obtain desired UO₂ powder characteristics for achieving high sinterability during pellet fabrication. The present paper discusses the effect of critical parameters of precipitation, calcinations and reduction on final product and successful optimization of process parameters resulting in increase of production rate by 50%. (author)

[en] The paper discusses a method developed for the determination of uranium in uranyl nitrate raffinate (UNR) generated through sodium di-uranate (SDU) process using inductively coupled plasma atomic emission spectrometer (ICP-AES). High concentration of Na in UNR limits the direct determination of uranium in ICP-AES. Therefore, selective extraction of uranium from UNR using tri-n-octyl-phosphine oxide (TOPO) and stripping by ammonium carbonate was followed. Effect of sodium on estimation of uranium is discussed. The method has been validated by standard recovery of spiked real time UNR samples with known amounts of uranium CRM (Merck-HC42984673). The developed method compared well with EDXRFS and Redox titrimetric methods. (author)

[en] The present paper describes a new analytical method developed for direct determination of boron in steels using radio frequency glow discharge optical emission spectrometer. 'Single parameter alternative method' technique has been used to optimize the various experimental conditions of glow discharge plasma such as forward power, gas pressure inside plasma chamber, pre-integration time, and integration time. Different emission lines for boron were studied and inter element interference effect is also discussed in the paper. A complete statistical analysis has been done to validate the developed method. A RSD of less than ±5% is achieved for boron in the range of 0.0010-0.020% in Steels using this method. (author)

[en] Determination of rare-earth elements like Ce, Sm, Eu, Gd, Dy, Er at trace levels in uranium process stream samples has been investigated by ion-interaction chromatography using C18 column, cation exchange based pre-concentration column (PCC). A mixture of α-hydroxy-iso-butyric acid and octane sulfonic acid is used as eluent after separation of uranium by solvent extraction. The trapping of analytes by PCC is found to be maximum in the pH range of 2.9-3.7 of sample solution. The spiking standard recovery for each analyte was found to be more than 90% and the method can be employed regularly. (author)