Investigating mechanical behavior and radiation resistant of fuel rods clad in nuclear power plant

The important factors for selection of material for use in nuclear reactors is similar to those for other engineering applications. There are however other parameters which are of importance when materials are going to be used in high radiation environments. These parameters are compatibility in intense nuclear radiation field, high resistance against corrosion and other characteristics such as thermal conductivity, machinability and suitable welding properties. This factors discussed in chapter one. In additions to the materials used as fuel, moderator, controls, etc., which have clear and stringent nuclear requirements, other materials may be necessary in a reactor to provide structural strength and other desired properties. For a materials used in a reactor core, the single most important property is its capacity for neutron absorption. Other properties, such as temperature and radiation stability, mechanical strength, corrosion resistance, etc., also receive much attention in selecting material for a specific application. Obviously, far more can be said about each of the potential metals than is possible in chapter two. We shall limit our attention to those metals of current nuclear interest, i.e., aluminium, beryllium magnesium, zirconium, austenitic stainless steels, nickel base alloys, and in factory metals (Nb and Mo). Interactions between matter and different radiations like Neutrons, protons, Gamma , Beta and Alpha rays in nuclear reactors induced important changes in properties of materials.There are five mechanism responsible for radiation induced changes in solids: ionization, vacancy formation, interstitial formation, creation of impurities caused by nuclear reactions and displacements spikes under the local thermal environment. Due to presence of many electrons in metals ionization does not play a major role in metals only the other four mechanisms are relevant to metals and their alloys. Generally speaking formation of many vacancies and interstitials in metal lattice under irradiation causes increased strength and hardness but decreases ductility in metals.The increase in strength and hardness depends on obstacles that prevent the motion of dislocations. The clustering of point defects are responsible for these changes. Irradiation also induces instabilities in phases due to enhancement of diffusion, solute segregation, precipitate formation, order- disorder transformation and resolution of small precipitates. From the microscopic point of view accumulation of vacancies accompanied by formation of He and H2 gases under irradiation cause an increase in volume which results in swelling and eventually ends up with embrittlement of metals. This subject was described in chapter three Zirconium and its alloys are the best structural materials for fuel cladding of BWR and PWR reactors core. The working condition in the core of nuclear reactor are very serve, respect temperature and radiation dose. It should be realized that, if fuel cladding receive damage and get cracked, the first cooling cycle and the maine equipment will be contaminated with active materials which cause additional environmental problems. Furthermore, replacement of fuel rods are very costly. Therefore, for increasing life time of fuel cladding and minimizing damage, the effect of radiation and heat on Zirconium and its alloys must be investigated. This subject was described in chapter four.The mechanical behavior and radiation resistant of fuel cladding in PWR reactor (specifically WWER ) have been investigated which is described in chapter five. Result, discussion and final conclusion are summarized in last chapter and also several points for improvement have been offered