الفهرس 
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Abstract
The desire to meet the needs of a high energy-hungry world without the carbon emissions associated with fossil-fuel-fired power plants has caused many companies to consider nuclear energy. According to the World Nuclear Association, as of October 2011 there were 432 commercial nuclear reactors operating worldwide with an additional 63 reactors under construction. Another 152 reactors were planned and another 350 nuclear reactors proposed for construction. These 502 additional nuclear reactors were expected to be operational by 2030 [1, 2].
According to the nuclear reactor design, removal of a quarter to a third of the nuclear fuel rods in the reactor was performed approximately every 12 to 24 months. These spent nuclear fuel rods were normally placed into a temporary on-site storage facility where the spent fuel rods were cooled for at least a year and typically several years. The spent fuel rods were kept in wet storage containers until they were sufficiently cooled to transfer them to another dry storage [2].
Many nuclear power plants have used specially designed storage racks and containers or casks made from boron-containing stainless steel as a shielding material to control the flow of thermal neutrons in the spent nuclear fuel bundles, or rods. These racks or casks were designed to hold 40 to 60 rods [1]
Nuclear power reactors are characterized by the high radiation field’s existence; high temperature and the requirement of materials possess special properties. The radiation fields and high temperature have a profound effect on the properties of the structural materials. The nuclear reactor materials must meet the specifications of strength and reliability. The demands of quality control on each component to be used in the nuclear reactor sectors are very stringent and are critical to their safe and efficient usage. Currently, new designs for nuclear reactors are coming forward and some of them are in operation because the first generation reactors come to the end of their operating lives [1-3]. In the field of design and construction of nuclear reactors, reactor structural materials play very crucial role for a safe, reliable and economic operation of nuclear power plants [4]. Materials used in nuclear reactors encounter hostile environment and aggressive medium during service, and are expected to retain their structural and metallurgical integrity over a long period of their using [5].
The major challenges of reactor materials are the effect of radiation on embrittlement, creep, erosion, corrosion, radiation induced growth, swelling, stress corrosion cracking, hydrogen and helium embrittlement, hardness and ductility [4-5]. In order to realize a high degree of reliability and at the same time meet the imposing challenges, material specification and acceptance criteria are extremely stringent and the products have to undergo a detailed testing and characterization prior to their use [4-5].
Now, it is important to produce reactor structural materials to resist harsher irradiation environment and higher temperatures to ultimately support rapid combustion. [6].
The best material that the reactor structural components are made of and has many uses in the nuclear domains is stainless steel (SS). Stainless steel alloys meet the desirable conditions because of cost, availability and manufacturing limitations. Austenitic stainless steels are the most common material used in the core of the nuclear power reactors [7-8].
2. Objectives and experimental
approach:
In the present work, a series of modified high Borated (SSB) stainless steels were developed to be used in the nuclear domains. SS304Mo and SS316 austenitic standard stainless steels were used as reference materials. All investigated samples were modified at the Central Metallurgical Research and Development Institute (CMRDI), Eltebbin, Helwan, Cairo, Egypt. Many experimental and theoretical studies were made to show the capability of the modified stainless steels to be used in many parts inside nuclear reactors.
Our aim is to develop in-house borated stainless steels alloys with stable micro-structure and mechanical properties under exposure to long-term thermal neutron irradiation as well as adequate ductility and impact resistance to be used as a structural material of the nuclear reactor.
In this regard, firstly, Six grades of stainless steel alloys with a boron addition varying up to 0.125 wt% and a Titanium content up to 0.382 wt% as well as standard stainless steel grade SS316 and standard stainless steel SS304 modified with Mo addition (SS304Mo) were prepared using pilot plant induction furnace melting unit then followed by hot forging and solution treatment.
Secondly, the effect of both boron and titanium on the structural properties of the investigated stainless steels was carried out using microstructure observation which was examined using optical microscopy.
Thirdly, the mechanical properties of the modified stainless steel alloys were investigated using, Vickers hardness test, tensile test (Yield strength, Ultimate tensile strength and Elongation) and impact absorption energy at room temperature.
Fourthly, comparing the corrosion rate (μm/y) between the modified high boron and the titanium stainless steels in 3.5 weight % NaCl, the prepared standard stainless steels was carried out.
Fifthly, the attenuation properties of the studied stainless steels were measured for pure gamma ray, slow neutron and total slow neutron fluxes and the available theoretical comparison was carried out.
3. Significance of the study
The study presented in the thesis is significant for two main areas in the nuclear science and engineering.
Nuclear materials: this study represents the study of materials used in nuclear domains like the nuclear power reactors which required materials of high hardness, ductility and high corrosion resistance, these materials that may use in various sectors inside the nuclear reactor.
Nuclear safety: the study is especially important for nuclear reactor safety and other high radiation mediums. In this regard, the attenuation capability of the selected stainless steel alloys was carried out for both gamma rays and neutrons