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Nuclear Power Plants Dr. Ervin Rácz, Ph.D. associate professor Motivating factors 1) It is positive, if the graduating electric engineers (or engineers) have knowledge about wide spectrum of power plants nuclear power plants are part of wide spectrum of power plant knowledge transfer of nuclear power plants at Power System Department was missing so far 2) There are articles published about operation and/or failures of nuclear power plants in the media. Widen knowledge about nuclear technology helps the civilian persons to understand and see clearly the given news. 3) Forever questions: o It is good or bad using nuclear power plants? Do we need or do not need nuclear power plants? o Should we prefer or do not prefer energy generation based on nuclear power plants? o What are advantages? What are disadvantages of using nuclear power plants? 4) You might be decision makers in nuclear topics in your working place in the (near) future o You must balance correct, exact, precise information o Knowledge is needed to take decision! Lecture #1. Motivating factors 5) Energetics concept of the Hungarian Government for the near future: o New energy law What is the source of the electric current? Renewable: Nuclear energy: According to the current plans, our Government plans to cover the significant part of the energy used in Hungary using nuclear power plant(s) working within the borders of Hungary. Nuclear power reactors will generate significant part of electric energy for Hungarians. Coal: Oil: Natural gas: Import: Source: Ministry of National Development Lecture #1. Energy generated by burning of coil and oil will be decreased in the future.. Hungarian Government decided: - Lifetime extension and modernization of Paks I. Power Plant - Extension of Paks I. Paks II. project. Topics 1. 2. 3. 4. 5. Elements of Nuclear Physics Detecting nuclear radiations, radiation detectors History of Nuclear Physics; Beginning of Nuclear A Nuclear Power Plant Types of Nuclear Reactors based on usage of the reactors 6. Generations of Nuclear Power 7. Nuclear Reactors in Hungary 8. Mini or small Nuclear Power Plants 9. Reactor Safety, Radiation Safety 10. Nuclear Accidents, abnormal operations 11. Nuclear Power plants and Environmental Protection 12. Fusion, Fusion Devices, Fusion Power Plants 13. Natural nuclear reactors or Nuclear Reactors in the Nature Lecture #1. Elements of Nuclear Physics Chapter 1. Lecture #1. Structure of a Nucleus 1. Henry Antoine Becquerel (1852 – 1908): o 1898: experimental investigation of radiation of uranium pitchblende o Packaged uranium pitchblende leaved on a photopaper o Checking the photopaper great trace on the paper o Intensity of the radiation was proportional to the strength of the observed shadow o Radiation originated from the uranium pitchblende propagates spontaneously. new name: o Lecture #1. nuclear radiation (radioactive) 1903: Nobel price in Physics Generation of X-rays Generation of x-rays Source: http://www.hitachi-hightech.com/global/products/science/tech/ana/xrf/descriptions/index.html/ Lecture #1. Structure of a Nucleus 2. Marie Sklodowska Curie (1867 - 1934) és Pierre Curie (1859 – 1906) o Two new elements came out from uranium pitchblende radium and polonium o They radiate stronger then the uranium pitchblende itself o New elements: radium and polonium Lecture #1. Structure of a Nucleus • Thomson 1897: o Plum-pudding model of an atom o In the globally natural atom (like in a sphere) the positive charge distribute uniformly. o Electrons sit in the uniform positive material, like plums in pudding or raisins in a scone „pudding”– positive charged part „plums or raisins” – negative electrons Lecture #1. Rutherford Scattering Experiment Geiger – Marsden Experiment • • • • University on Manchester 1909 – 1911 Hans Geiger, Ernest Marsden Leading by Prof. Ernest Rutherford • In order to investigate of the structure of Gold some scattering experiments were designed and ran Gold foil is bombed by alpha particles (=nucleus of Helium) • Lecture #1. • Expected results: - alpha particles will slow down - alpha particles will keep direction of its propagation - alpha particles penetrate through the gold foil - alpha particles will heat the detector surface directly behind the gold foil target • Real results: - direction of the propagating alpha particles has been changed after the collision with gold - alpha radiation backscattering was observed (deflected radiation) Rutherford Scattering Experiment Geiger–Marsden Experiment • Explanation: Lecture #1. o If the structure of Gold atom would work according to the plum pudding model, than the backscattering (deflecting) of alpha particles cannot be observed. Particles would slow down keeping their direction. o Propagation of alpha particles deflected the plum pudding model cannot be valid. o Heavy and positively charged local scattering centers have to be presented inside the atom o The atom has nucleus. The nucleus is positively charged. The nucleus has big mass. Structure of a Nucleus 3. Sir Ernest Rutherford (1871 - 1937) • Scattering experiment o Nucleus of an atom exists or in other words there is nucleus of an atom! o Size of a nucleus can be predicted from the scattering angle of the alpha-particles. o Size of a nucleus: 2R, o Taking into account the size, the radius of a nucleus is: R Lecture #1. Radius of a Nucleus • Definition (radius of a nucleus): Radius of a nucleus can be characterized by the size of the charge distribution inside the nucleus. In other words, the radius starts in the center of a nucleus and ends at the edge of the impact area of forces acting inside the nucleus. Symbol: R • Formula of the radius of the nucleus: 𝑅 = 𝑅0 ∙ 𝐴1/3 𝑅0 = 1,2 𝑓𝑚 𝑓𝑒𝑚𝑡𝑜𝑚𝑒𝑡𝑒𝑟 , 1 𝑓𝑚 = 10−15 𝑚 In the atomic physics: 1 fermi means: 1 fm = 1 fermi 𝐴 = 𝑚𝑎𝑠𝑠 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑛 𝑎𝑡𝑜𝑚 Lecture #1. ?? What is this? Charge of Nucleus, Mass of an Atom • Antonius Johannes van den Broek (1870 - 1926): o 1913: Charge of nucleus comes out as the multiplication of the charge unit and the atomic number (of an atom). • Francis William Aston (1877 - 1945): o 1919: Mass of an atom is always proportional to an atomic mass unit (AMU) multiplicated by a positive integer (it came out from mass-spectrometer measurements lead by Aston) o The atomic mass unit was higher than the electron mass. It was comparable to the mass of the ground state Hydrogen atom. o Mass of an atom can be characterized by the atomic mass. Symbol: A (it is called after Aston) • Definition (atomic mass unit, AMU): o A1 o later: 1/12 part of the mass of the ground state carbon atom 12 C. In other words: o 1 𝐴𝑀𝑈 = 931,5 Lecture #1. 𝑀𝑒𝑉 𝑐2 = 1,6603 ∙ 10−27 𝑘𝑔 AMU, Mass Number of an Atom The atomic mass unit, AMU: 𝑀𝑒𝑉 1 𝐴𝑀𝑈 = 931,5 2 = 1,6603 ∙ 10−27 𝑘𝑔 𝑐 Mass of one proton : 𝑚𝑝 = 1,007 𝐴𝑀𝑈 Definition (mass number of an atom): The mass number of an atom (signed by A) is the atomic mass which is rounded to integer numbers and denoted by atomic mass unit. For proton and Hydrogen: Ap = AH = 1 Definition (signed the chemical elements): In order to show the chemical elements, we use the following form: Lecture #1. A: mass number Z: proton number X: chemical symbol A X Z Mass Density of a Nucleus • Taking the nucleus as a sphere, the volume: 𝑉 = 4 3 𝑅 𝜋 3 • The radius of a nucleus is (see it before): 𝑅 = 𝑅0 𝐴1/3 , so 𝑅3 = 𝑅0 3 𝐴 , It means that 𝑉 = • Mass density of a nucleus: 4 𝑅0 3 𝐴 3 𝜋. 𝑚 𝐴 3𝐴 3 𝜌= = = = 3 𝑉 𝑉 4𝑅0 𝐴𝜋 4𝑅0 3 𝜋 • For example: if 𝑅0 = 1,2 𝑓𝑚, 𝑡ℎ𝑒𝑛 𝜌 = 2,3 ∙ 1017 𝑘𝑔 𝑚3 • Consequence: Mass density of a nucleus is independent of the mass number (A). Lecture #1. Parts of a Nucleus • At the beginning of XX. century: Nucleus consists protons only. • But: 𝐴 ≈ 2𝑍. The nucleus cannot hold protons only, because this way the nucleus cannot be electrically natural. • Suppose of Rutherford: the nucleus holds electrons, too. This contradicts to the Heisenberg inequality proof. • James Chadwick (1891 - 1974): o 1932: discovery of a new particle: neutron . • Werner Karl Heisenberg (1901 - 1976) and Igor Yevgenyevics Tamm (1895 - 1971) o They found the neutron in the nucleus o Theory of: Nucleus consists of protons and neutrons Lecture #1. Definitions • Definition (nucleon): Protons and neutrons consist the nucleus calls as nucleon. We use to sign the number of nucleons by N. • Consequence: The mass number of an atom can be defined by the number of nucleons of the nucleus. As it is given here: A=Z+N • Definition (isotopes): Nuclei with same proton numbers but different mass numbers are isotopes. • Definition (isobars): Nuclei with same mass numbers but different proton numbers are isobars. • Definition (isotones): Nuclei with same neutron numbers use to call as isotones. Lecture #1. Map of Isotopes • • • Map of nuclei Small squares symbolize the nuclei Stable nuclei: black squares • Close to the stable nuclei: nuclei with longer half-life Far from stable nuclei: nuclei with fast decay • Proton drop-off line (it is the upper border of nuclei with fast decay. Above of it the nucleus emits proton(s) to get energetically more stable position. Above of the proton drop-off line the nuclei are not stable, but they emit protons immediately. • Neutron drop-off line ( it is the lower border of nuclei with fast decay). The nuclei do not exist here, because the nucleus emits a neutron immediately. Lecture #1. Momenta of Nuclei • • • • Definition (spin of nucleus): Net of the angular momentum (spin) and the orbital angular momentum of the nucleus is called as spin of the nucleus. Nuclei have spin with half-number. ℎ The spin of nucleus can be written as: s=n , where n is integer or 2𝜋 half-number Definition (Bohr-magneton): Quantum of the magnetic dipole momentum of an electron inside an atom calls as Bohr-magneton. 𝑒 ℎ 𝑀𝐵 = ∙ 2𝑚𝑒 2𝜋 • Definition (magneton of nucleus): Quantum of the magnetic dipole momentum of a proton inside an atomic nucleus calls as magneton of nucleus: 𝑀𝐵𝑚 Lecture #1. 𝑒 ℎ = ∙ 2𝑚𝑝 2𝜋 Forces inside Nucleus = Nuclear Force • • • • Problem: Many protons stay together inside a small nucleus. Electric forces do not destroy the nucleus. Why?? The protons do not scatter into the space. Why?? Conclusion: Due to the nucleus exists and the nucleus stays in one volume, there must be a force which stick the protons together. Definition (force inside nucleus = nuclear force): The force which acts in between nucleons (inside nucleus) use to call as nuclear force. It is a very intense force but it has a very short range inside nucleus only. Nuclear forces are independent of charges of charged particles. The nuclear force is the same in between two protons and in between two neutrons. Introduced by Hideki Yukawa (1907 - 1981): o 1935: pion: In order to describe the forces in between nucleons. o -meson or pion are „messengers” or „intermediary particles” between two nucleons. o Nuclear force is described by -mesons or pions. Lecture #1. Nuclear Forces • Nucleons are not simple but complex particles. (Quarks, gluons) • Definition (strong interaction): The interaction in between nucleons use to call as strong interaction. This interaction sticks the nucleons together. Lecture #1. Simple Models of a Nucleus 1. Bonding energy: o Definition (bonding energy): Bonding energy is the energy of 𝐸𝑏 what is released when the nucleus is being built from its nuclear components. It means that: Z pieces of protons, N pieces of neutrons separately 𝐸𝑏 nucleus in one. Where 𝑚 is the mass of the nucleus, 𝑐 is the speed of light in vacuum: 𝐸𝑏 = 𝑍𝑚𝑝 + 𝑁𝑚𝑛 − 𝑚 𝑐 2 o Definition (bonding energy for one single nucleon): 𝜀𝑏 = • • 𝐸𝑏 𝐴 It gives information how the nucleon is bonded in the nucleus. It can be measured precisely by mass spectrometry. Lecture #1. Simple Models of a Nucleus Lecture #1. 1. előadás ΔE/A (bonded energy fells for one single nucleon, [MeV]) Simple Models of a Nucleus A (Mass number = number of nucleons in a nucleus) Lecture #1. Averaged bonded energy for one single nucleus in function of the mass number (A) Lecture #1. Simple Models of a Nucleus 2. Liquid drop model (developed by Weizsäcker): o basics: • Properties of sizes on nucleus mass density of a nucleus is constant (see it before) • The nucleus can be taken into account as incompressible liquid • The nuclei can be taken as many of small size balls with same radii and they are colliding each other • Bonded energy nuclear forces are saturated, nucleons can interact with neighboring nucleons Definition (liquid drop model) : The nucleus cannot be compressed, it has electric charge. The nucleus can be taken into account as fluid with electric charge and its surface is minimized (surface tension). o Comment: • Using the liquid drop model a semi-empiric bonded formula has been described. • The semi-empiric formula describes the bonded energies of the nuclei quiet well. good, usable model ! • The liquid drop model does not describe the exotic nucleii good. In other words, the model cannot be used for describing exotic nuclei. Lecture #1. o Simple Models of a Nucleus 3. Shell model for nucleus: o About the shell model: • The shell model is the application of the quantum mechanics for nuclei. • Potential acts in between the particles of the system must be used very well. Interaction between protons and neutrons is not well known difficult to describe • Mean-field approximation: Let us take that: Every nucleon moves in the same averaged potential field of the nucleus, and the averaged potential field of the nucleus is spherical. Main task is the calculate wave functions for the nucleus. Lecture #1.