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Components Of A Nuclear Reactor - Typical

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Components of a Nuclear Reactor - Typical Nuclear reactor core Reactor vessel Heat exchangers Boiler feed water pump Steam generators  Steam turbine Electricity generator Condenser Cooling tower  Containment building Control room Emergency Operations Facility Nuclear fuel Neutron moderator Neutron poison Coolant  Control rods

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    Components of a nuclear reactor
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    Components of a nuclear reactor - typical Nuclear reactor core Reactor vessel Heat exchangers Boiler feed water pump Steam generators Steam turbine Electricity generator Condenser Cooling tower Containment building Control room Emergency Operations Facility Nuclear fuel Neutron moderator Neutron poison Coolant Control rods
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    Materials in Nuclear Reactors Materials that are consumed - Fuel Materials that participate in energy transfer or reactions — Moderator, Coolant, control rod Materials that shield the radiations — Shielding material, steel, concrete Materials that hold the fuel — Fuel cladding Materials that hold the fuel pins or fuel bundles — Wrapper PERIODICALLY CHANGED - SHORT LIFE SPAN IN REACTORS Materials of construction of the reactor — Reactor vessels, grids, pumps, heat exchangers Materials of construction of the roof slab Materials of construction of the steam generator components - PERMANENT STRUCTURES 3
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    Materials in Nuclear Reactors Materials that are consumed - Fuel Materials that participate in energy transfer or reactions — Moderator, Coolant, control rod Materials that shield the radiations — Shielding material, steel, concrete
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    Nuclear Fuel Important Properties of Fuel Materials: Thermal Conductivity Thermal expansion Melting temperature (solidus temperature) Compatibility with clad, coolant Mechanical properties such as hardness, creep etc — Fissionable by neutrons of all energies Fissile Nuclides 235U 239pu 233U Natural U contains 0.7% 2351J • Fertile Nuclides - Can be converted to Fissile Nuclides 238U 232Th
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    • Fuels Natural I-J02 Enriched U02, (U.21 Pu.79)02, (U.28Pu.72)02 U-19Pu-l OZr Advantages: High Fissile atom density Nuclear Fuel • Chemical Form - Oxide, Carbide, Nitride, Metal or Alloy (U.45Pu.55)C, (U.30Pu.70)C PHWR BWR FBTR PFBR Future FBRs High Breeding Ratio and Low doubling time Disadvantages: + Anisotropic expansion and dimensional instability + Low melting point Low operating temperature
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    FISSION CROSS SECTION 104 105 Energy (eV) 106 Cross section (barns) as a function of neutron energy for 235U, showing increase in fission probability with lower neutron energy
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    FISSION CROSS SECTION Probability of fission events is determined by fission cross section, which is dependent upon the speed (energy) of the incident neutrons. For thermal reactors, high-energy neutrons in the MeV- range are much less likely to cause further fission. The newly-released fast neutrons, moving at roughly 10% of the speed of light, must be slowed down or "moderated", typically to speeds of a few kilometres per second, if they are to be likely to cause further fission in neighboring 2351J nuclei and continue the chain reaction. This speed is equivalent to temperatures in the few hundred celsius range.
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    Thermal Reactors Neutron sources generate free neutrons by a variety of nuclear reactions, and they are released with kinetic energies (KE) of several MeV. Neutrons, fast at birth are slowed down, ie moderated, using elastic scattering in light elements. The coolant acts as a moderator that slow down the neutrons before they can be efficiently absorbed by the fuel.
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    MODERATOR E 1 2 = —me 3 kBT 2 The energy of the neutron is lowered by predominantly elastic collisions i.e., the total kinetic energy and momentum of the system (that of neutron and nucleus) is conserved. As neutrons are very light compared to most nuclei, most efficient way of removing kinetic energy is by choosing a moderating nucleus that has near identical mass 10
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    MODERATOR Choice of moderator materials ' Low mass High scattering cross section Low absorption cross sections Commonly used moderators are light water, heavy water and graphite. Beryllium has been used in some experimental ones and hydrocarbons have also been suggested.
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    MODERATOR Moderating efficiency gives the ratio of the macroscopic cross sections of scattering, is, weighted by divided by that of absorption, Ea: For a compound moderator, example H20 or D20: moderating and absorbing effect of both hydrogen isotope and oxygen atom is used to calculate To bring a neutron from the fission energy of Eo 2 MeV to an E of 1 ev takes an expected n of 16 and 29 collisions for 1-120 and D20, respectively. Therefore, neutrons are more rapidly moderated by light water, as H has a far higher Eso However, it also has a far higher Ea, so that the moderating efficiency is nearly 80 times higher for heavy water than for light water. 12
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    MODERATOR Graphite moderated reactors Water moderated reactors Heavy water reactors — D20 Light water moderated reactors (LWRs) - H20 Light element moderated reactors - Li or Be moderated Molten Salt reactors (MSRS) - Li or Be moderated which are constituents of the coolant/fuel matrix salts LiF and BeF2. Liquid metal cooled reactors, with Pb or Bi coolant - Beo as moderator. Organically moderated reactors (OMR) - biphenyl and terphenyl as moderator and coolant.
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    Neutron reflector Neutron reflector is any material that reflects neutrons by elastic scattering. To cut down the neutron leakage losses from core Desired properties same as moderators The material may be graphite, Be, steel and also heavy materials like lead, tungsten carbide, or other materials. A neutron reflector can make an otherwise sub-critical mass of fissile material critical. Water Heavy Water Thermal Reflectors Beryllium Graphite
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    NEUTRON POISON A nuclear poison, also called neutron poison is a substance with a large neutron absorption cross-section in reactors, when absorbing neutrons is an undesirable effect. However neutron- absorbing materials, also called poisons, are intentionally inserted into reactors in order to lower the high reactivity of their initial fresh fuel load. Some of these poisons deplete as they absorb neutrons during reactor operation, while others remain relatively constant. 15
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    CONTROL ROD MATERIALS Control rods made of a nuclear poison are used to absorb neutrons, which means that there are fewer neutrons available to cause fission; so pushing the control rod deeper into the reactor will reduce its power output, and extracting the control rod will increase it. A control rod is made of chemical elements capable of absorbing many neutrons without fissioning themselves. The elements have different capture cross sections for neutrons of varying energies. The composition of control rod should be uniquely designed for each reactor. 16
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    CONTROL ROD MATERIALS - Selection Criteria Neutron absorption cross section Adequate mechanical strength Corrosion resistance Chemical and dimensional stability (under prevailing temperature and irradiation conditions) Relatively low mass to allow rapid movement Fabricability Availability and reasonable cost
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    CONTROL ROD MATERIALS Boron, Silver, Indium, Cadmium, Hafnium, Dysprosium, Gadolinium, Samarium, Erbium, Europium or their alloys and compounds: - e.g. high-boron steel, Ag-ln-Cd alloy, boron carbide, zirconium diboride, titanium diboride, hafnium diboride , gadolinium titanate, and dysprosium titanate. Element Boron Silver Indium Cadmium Hafnium Dysprosium Gadolinium Samarium Erbium Europium Thermal Neutron Capture Cross section 767 64 194 2450 72 920 49000 5922 160 4600 B4C B4C BWR (Clad in 304 PWR (Clad in CW Ag- 50/01"+50/0Cd 304 SS, Inconel 627) LMFBR 18
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    CONTROL ROD MATERIALS Boron - Due to different cross sections of 10B and 11 B, boron containing materials enriched in 10B by isotopic separation are frequently used. The wide absorption spectrum of boron makes it suitable also as a neutron shield. Hafnium - has good mechanical strength, can be easily fabricated, and is resistant to corrosion in hot water. Hf can be alloyed with small amounts of other elements; e.g. tin and oxygen to increase tensile and creep strength, iron, chromium and niobium for corrosion resistance, and molybdenum for wear resistance, hardness, and machine ability - designated as Hafaloy, Dysprosium titanate is a new material currently undergoing evaluation for pressurized water control rods. Dysprosium titanate is a promising replacement for Ag-In-Cd alloys because it has a much higher melting point, does not tend to react with cladding materials, is easy to produce, does not produce radioactive waste, does not swell, and does not outgas. Hafnium diboride is another such new material. It can be used standalone or prepared in a sintered mixture of hafnium and boron carbide powders.
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    Thermal neutron capture cross-sections of element 0.00019 0.0035 0.007 0.0092 0.0096 1.3 0.03 0.034 0.04 2.1 0.063 0.171 0.171 0.172 0.184 0.232 0.3326 0.38 0.43 0.53 0.53 0.6 0.626 0.675 0.72 0.96 Mg Pb Si Zr Ca Na Sn 84 83 10 n 82 14 15 40 13 37 20 16 11 58 50 18 86 1.11 1.15 1.28 1.28 1.91 2.2 2.56 2.56 2.6 2.9 3.1 3.43 3.78 4.3 4.49 4.7 4.91 5.08 Zn Sr Ru Mo Ga Cr cu Sb 78 30 41 39 38 56 19 32 44 26 42 31 24 81 29 33 28 52 51 23 6.8 6.9 7.37 7.57 8.98 11.5 11.7 12.8 13.3 15 18.3 20 20.6 23.4 23.9 25 27.2 29 Se os Ta 35 46 90 92 57 59 34 88 25 76 74 43 73 65 54 36 21 55 6.09 6.2 34.8 35.5 37.2 49 63.6 65 70.5 75.3 79 84 89.7 98.7 100 104 144.8 160 Ho Cm Lu Au 22 53 70 17 27 60 67 95 96 71 75 79 69 72 45 99 160 168.4 180 194 200.6 374 425 515 710 767 920 1017.3 2450 2900 4600 5800 5922 49000 Pm In Pa Ir Dy Pu Cd Cf Eu Sm 68 61 93 49 91 80 77 89 97 66 94 48 98 63 100 62 64
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    SHIELDING MATERIAL To protect personnel and equipment from the damaging effects of radiation e Good moderating capability Reasonable absorption cross section C Cost and space availability e Neutron, a, ß and Y shielding C Both light and heavy nuclei are preferred WATER PARAFFIN POLYETHYLENE Boral (B4C in Al matrix) Concrete 21
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    Nuclear Reactor Coolant A coolant in a nuclear reactor that is used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment. Frequently a chain of two coolant loops is used because the primary coolant loop takes on short-term radioactivity from the reactor. Low melting point High boiling point Low vapor pressure Low density Low neutron absorption cross section High thermal conductivity Non toxic Low pumping power No induced radioactivity 22
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    Nuclear Reactor Coolant Coolant Light water at 155 bar Mercury NaK eutectic Sodium F-Li-Be Lead Lead-bismuth eutectic M.pt -38.83 oc -11 oc 97.72 oc 459 0 C 327.46 oc 123.5 oc B.pt 345 OC 356.73 oc 785 oc 883 oc 1430 oc 1749 oc 1670 oc 23
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    Reactor Type BWR PWR HWR AGR HTGR GCFR LMFBR LWBR ape e s; sp Major Power Reactors and their Components A1203-B4C B4C B4C B4C B4C H20 Coolant H20 H20 D20 C02 He Primary U 02a U 02a IJ02a IJ02a UC2C (Th02) (U02) (U-Pu)02a (U-Pu)02a (U-Th)02a par IC es Fuel Alternates I-J02a, l.J02a (U-Pu)02a (U-Pu)02a (U-Pu)02C, (U- Th02)c Pu)Na, (U-Pu)02b Control Rod Primary B4C, IJ02- Gd203 Alternates U02-Gd203 Gd203-A1203, Eu203 ere-pac; c coa e


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