A review of radiation effects in nuclear reactor materials has been made; the irradiation effects have been correlated with the crystal structure of the materials. Five phenomena, irradiation hardening, irradiation embrittlement, irradiation creep, irradiation growth and void swelling that occur in materials by neutron irradiation in a reactor environment have been discussed with a view to explaining the physics of the phenomena and the engineering consequences. Metallurgical approaches for improving the irradiation performance of materials and for developing new alloys with better resistance to radiation damage have been pointed out.
The importance of nuclear energy in meeting future energy demands has been well-recognlsed and a variety of nuclear reactor systems have been developed. Inherent characteristics of nuclear technology like neutron economy and neutron irradiation-induced degradation in properties of materials require stringent control of material purity and necessarily limit the choice of candidate materials. Hence safe, reliable and economic operation of nuclear fission reactors, the source of nuclear power at present, requires judicious choice, careful preparation and specialised fabrication procedures for fuels and fuel element structural materials. These aspects of nuclear fuels (uranium, plutonium and their oxides and carbides), fuel element technology and structural materials (aluminium, zircaloy, stainless steel etc.) are discussed with particular reference to research and power reactors in India, e.g. the DHRUVA research reactor at B~c, Trombay, the pressui'ised heavy water reactors (PHWR) at Rajasthan and Kalpakkam, and the Fast Breeder Test Reactor (FBTI~) at Kalpakkam. Other reactors like the gas-cooled reactors operating in UK are also mentioned. Because of the limited uranium resources, India has opted for a three-stage nuclear power programme aimed at the ultimate utilization of her abundant thorium resources. The first phase consists of natural uranium dioxide-fuelled, heavy water-moderated and cooled PHWR. The second phase was initiated with the attainment of criticality in the FSTR at Kalpakkam. Fast Breeder Reactors (FBR) utilize the plutonium and uranium by-products of phase 1. Moreover, FBR can convert thorium into fissile U-233. They produce more fuel than is consumed-hence, the name breeders. The fuel parameters of some of the operating or proposed fast reactors in the world are compared, rBTR is unique in the choice of mixed carbides of plutonium and uranium as fuel. Factors affecting the fuel element performance and life in various reactors e.g. hydriding of zircaloys, fuel pellet-cladding interaction etc. in PHWR and void swelling, irradiation creep and helium embrittlement of fuel erement structural materials in FBR are discussed along with measures to overcome some of these problems.
The ushering in of the era of high technology in our country witnessed the emergence and growth of several new technologies which are either totally unconventional or !ess common in otherwise well known and established areas of industrial practice. A vivid example of the second category of advances is found in the development of extractive processes for obtaining the less common metals particularly required for service in nuclear, aerospace and electronics industries. In this paper, the growth of research and development in rare metals extraction in India is surveyed from its infancy in the fifties to the present stature of a firm tboted technology accredited with several directed achievements and well-developed maturity.
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