TECHNOLOGICAL ACHIEVEMENTS

My contributions cover a wide ranging research and development programmes having direct and immediate bearing on the development of technology for the setting up of fast breeder reactors in the country. I was responsible for setting up metallurgy and materials related laboratories and nurturing one of the most vibrant research and development groups. This group at Kalpakkam is today recognised both nationally and internationally as a well respected and leading school in the area of mechanical and physical metallurgy, welding and fabrication metallurgy, corrosion science and technology and non-destructive evaluation of engineering materials and components. Our efforts in the area of materials technology have led to the indigenous development of a special (D-9) stainless steel stabilized with titanium with the most stringent requirements of cleanliness for fuel cladding and wrapper application in fast breeder reactors and extra clean nuclear grade 9Cr-1Mo steel for steam generators.

I have been responsible for the design and commissioning of a highly sophisticated laboratory (Radio Metallurgy Laboratory(RML) for post-irradiation examination of fuel elements and other highly radioactive materials. Equally significant contribution involves the setting up of the Materials Development Laboratory for characterisation of reactor materials currently in use and evaluation of potential candidate materials for future applications. Realizing the importance of neutron radiography, a Neutron Source Reactor KAMINI has been set up at RML, IGCAR which has added significantly to our capability of non-destructive evaluation of radioactive materials and other materials of strategic importance for defence and space programmes.

My extensive research efforts have provided excellent R&D support in the area of materials for Fast Breeder Test Reactor (FBTR) project as well as arriving at selection of materials and their specification for Prototype Fast Breeder Reactor (PFBR). The work in some key areas like determining permissible degrees of cold work in fabricated components of stainless steels without resorting to solution treatment, identification of welding parameters and processes for producing sound welds and the influence of the number of weld passes and specimen dimensions on the mechanical properties has provided vital and invaluable information that facilitated taking decisions during fabrication of FBTR components.

I have planned and conducted an extensive programme on the testing and evaluation of various materials used in the construction of FBTR. These studies, in addition to assuring the designer about the long term properties assumed in the design of the reactor have generated base line information against which have deterioration in properties due to sodium exposure and irradiation would be assessed. Recognising the importance of conducting long term creep tests with a view to refining life prediction techniques for components operating at elevated temperatures and for determining metallurgical stability of the materials under plant operating conditions, creep tests running more than 12 years have been performed on stainless steels procured for FBTR. It is established that minor variations in chemical composition from heat to heat can lead to major changes in the mechanical properties. These studies have aided in arriving at specifications for nuclear grade steels for PFBR and provided much needed information for assessing the life of reactor components subjected to creep and creep-fatigue interaction.  

The engineering components at high temperatures encounter during operation, conditions simultaneously of creep and fatigue. For accurate prediction of life, it is essential that these interactions are clearly understood. My work on austenitic stainless steels and ferritic steels has clearly identified various damaging processes in low cycle fatigue at high temperatures. Through very carefully and meticulously planned experiments, it has been shown that damage depends on micro-structural parameters like grain size, prior cold work, precipitates and various test variables like strain range, temperature, frequency of load application and hold periods. A notable contribution to this area is the finding that creep and fatigue properties of thick components like tube sheet forgings are inferior to properties of bar and tube products of 9 Cr-1Mo steel. New design curves for such components have been generated thus ensuring high confidence and improved reliability of the components. These studies have broadened our understanding of the development of damage during high temperature low cycle fatigue which is vital for both development of materials resistant to high temperature fatigue and accurate prediction of life of components.

I have made important contributions to the welding metallurgy of stainless and special steels and in non-destructive testing and development. Activities in these areas were initiated from scratch at Kalpakkam and the pre‑eminent position at Indira Gandhi Centre for Atomic Research today in these specialisations is a noteworthy achievement.

It is recognised that welds are weak links in structures. Owing to the lack of understanding of the behaviour of welds and information about their mechanical properties, the design codes use empirical rules for welded structures often with unrealistic conservatism. I have made singular contributions both to the understanding of the mechanical behaviour of welds at elevated temperatures and micro-structural evolution in stainless steel weldments on thermal ageing and during thermal cycles seen in multi-pass welding. This work has been recognised by the Indian Institute of Welding (IIW) by conferment of research awards on me as well as Keith Hartley Memorial (Lecture) Medal of IIW. An investigation of particular significance relates to the study of effect of weld defects on low cycle fatigue of welds. It is now understood what kind of defects are most damaging and should be avoided for improved performance.

Non-destructive examination (NDE)techniques play a very important role for structural integrity assessments of plants and components through quality control and inspection, during manufacture/fabrication and in-service inspection and surveillance of operating plants. Due to initiative taken by me 26yrs. ago IGCAR today has the most capable group in this area in the country. I have foreseen the importance of both established techniques and early adoption of emerging front line NDE techniques like acoustic emission, laser holography and interferometry and infrared thermal imaging and has built and guided the NDE groupto possess expertise in a wide range of NDE techniques. The expertise of this group has been repeatedly utilised by the operating nuclear power plants and heavy water plants of Department of Atomic Energy as well as by other organisations like Defence Research Development Organisation, Indian Space Research Organisation and industries.

Most of the materials and core components like fuel cladding and subassembly wrappers of FBTR have been imported. I have stressed the need to develop indigenously these materials of strategic importance. Through efforts at IGCAR, Ti-modified special stainless steel (D-9) with most stringent requirements of cleanliness for fuel cladding and wrapper applications has been developed in the country. This involved systematic investigations on laboratory scale melts before commercial production could be taken up at MIDHANI. Another remarkable success has been the development of the technology of manufacturing of thin walled fuel tubes to exacting tolerances and hexagonal cans for fuel subassemblies in collaboration with Nuclear Fuel Complex, Hyderabad.

It is well known that heat to heat variations in stress rupture properties of structural alloys is often very large. However, multiple heat stress rupture correlation has received only limited attention in the literature despite its potential benefits.In a recent comprehensive study, my group (Ray, Sasikala and Rodriguez) has proposed a novel generic method for extending any single heat rupture correlation to the corresponding multiple heat version using two heat-indexing constants. A novel single heat stress rupture correlation has been proposed that attempts to incorporate in a semi-empirical manner the broad features of the mechanisms of creep void growth; taking stress rupture data for 11 heats of a 9Cr-1Mo steel it has been shown that the efficacy of this new single-heat correlation compares favourably with the best of the more popular stress rupture parameters. The corresponding multiple heat version was successful in simultaneously correlating the data from all the eleven heats. The comprehensive study established that in this instance two linearly independent heat-indexing constants are necessary, but points out the situations in which one such constant could suffice. Empirical correlations between material chemistry and the heat-indexing constants are derived by a trial and error method which attempts to optimize between the large number of chemistry variables on the one hand and the small number of heats on the other. The strategy for characterizing a "new" heat using only three short duration rupture tests was evolved, where such predictive correlations, if available, can be advantageously utilized. The studies have been now extended to a number of stainless steels and different product forms (tubes, rolled plates, forgings etc.)

An understanding of the various mechanisms of materials ageing and degradation is a crucial component of any strategy for life assessment and extension.It is in this context that my four decades of R&D experience towards understanding damage caused by creep, fatigue, creep-fatigue interaction, irradiation, corrosion and other environmental effects, dynamic strain ageing and micro structural degradation by thermal ageing, chaaracterising the damage through micro structural and non-destructive evaluation and developing advanced approaches for structural integrity assessment (structural mechanics, fracture mechanics and damage mechanics) has been unique. My expertise has been utilised not only by DAE units but also by defence and aerospace agencies and a variety of industries both in the public and private sectors.

On December 1, 1992, I was appointed as Director, IGCAR.  In this capacity, when I held till end of October 2000,  I  guided and directed all the activities in this multidisciplinary Centre which include in addition to Metallurgy and Materials, Reactor Physics, Reactor Engineering, Chemistry and Fuel Reprocessing and Management of various projects related to the Indian Fast Reactor Programme. I have tried to provide the inspiration and motivation to all the individuals, Sections, Divisions and Groups to work as a united team in achieving the following important milestones for FBTR, which hitherto was operated at a maximum power level of  1 Mwt only:

Activities carried out at IGCAR during my tenure as Director have led to significant strides towards the readiness to start construction of PFBR in the year 2001.  The evolution of an optimised and economical design with 2 loops, four intermediate heat exchangers (IHX) and eight steam generators has proceeded concurrently with the manufacturing technology development of most of the plant components including the main vessel, the inner vessel, the primary sodium pump, the grid plate, the steam generator, the control rod drive mechanism, the roof slab and fuelling machines.

Closing the fuel cycle is an integral part of FBR development. The Lead Mini Plant (LMP) a demonstration plant for the reprocessing of the carbide fuel will soon be commissioned. Following this, the Fast Reactor Fuel Reprocessing Plant (FRFRP) for full scale reprocessing of FBTR will be completed in another two years.  In the Reprocessing  Development Laboratory (RDL) the campaign for extraction of U-233 from irradiated thorium rods is being continued.

I have established a high reputation as an effective S&T Manager and my experiences cover R&D management, Project Management, Technology Management and HRD for S&T activities.

(Placid Rodriguez)

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