LECTURE 9 NUCLEAR POWER GENERATION

1. LECTURE 9NUCLEAR POWER GENERATION Dr. Rostamkolai ECE 371 Sustainable Energy Systems

2. INTRODUCTION • If the current coal usage continues, the coal supply in the world will be depleted in 155 years • Nuclear energy as it is known today was highlighted by Einstein in 1905 • E = mc2

3. INTRODUCTION Theoretical research in controlled fission resulted in the first successful demonstration of a self-sustained chain reaction at the University of Chicago in 1942 as a part of the Manhattan Project Nuclear power plants were first developed for naval propulsion and energy production in 1950s (higher-specific-energy fuels)

4. INTRODUCTION • Expansion in US halted in 1970s • Overbuilt generation • Reduction in load growth • Most nuclear plants are light water reactors • Pressurized Water Reactor (PWR) – Most Common • Boiling Water Reactor (BWR)

5. PWR 2300 psi, 315oC

6. BWR 1000 psi, 285oC

7. HISTORICAL PERSPECTIVE The world’s first nuclear-powered electric generating plant was constructed by Soviet Union in 1954 – 5 MW The first US PWR was constructed and placed in service by Westinghouse at Pennsylvania in 1957 The first US BWR was constructed and placed in service by GE at California in 1957 – 5 MW

8. HISTORICAL PERSPECTIVE The following figure shows the number of nuclear plant orders placed annually 1973: Arab Oil Embargo 1979: Three Mile Island #2

9. INTRODUCTION

10. HISTORICAL PERSPECTIVE There are 439 nuclear plants in the world, with 104 of them in 31 US states

11. HISTORICAL PERSPECTIVE

12. HISTORICAL PERSPECTIVE

13. BACKGROUND Nuclear energy is obtained from the atom nuclei through a controlled reaction The possibility of harvesting the nuclear energy was first recognized in the 1930s and early 1940s The idea of obtaining large amounts of energy from small amounts of material was very exciting to the scientists

14. BACKGROUND An element’s chemical nature is determined by the number of electrons in its atom In a neutral atom, the number of electrons is equal to the number of protons in the nucleus The positive charge of protons are cancelled by the negative charge of electrons

15. BACKGROUND Radioactive

16. BACKGROUND Mass Number = (Number of Protons) + (Number of Neutrons)

17. BACKGROUND • The number of protons in a nucleus determines the elements • The number of neutrons determines the isotope • Example • Uranium nucleus has 92 protons • If it has 143 neutrons, it is Uranium-235 • If it has 146 neutrons, it is Uranium-238

18. BACKGROUND • There are 14 known isotopes of uranium • Approximately 1000 distinct isotopes have been identified experimentally • They are grouped into 103 elements with names • There are 4 more elements shown in charts, but two are un-named

19. BACKGROUND • Of all identified isotopes, 279 of them are stable • They are nuclei that do not experience natural decay (disintegration) • The rest have some intrinsic nuclear imbalance which eventually causes them to change their structure • Such changes always lead to a more stable isotope and involve the emission of some disintegration product

20. BACKGROUND • The emitted particles are • Electron beta decay • Helium nuclei alpha decay • All nuclei, except hydrogen H1, can be excited without altering its basic nuclear structure • They eventually return to their natural state by emitting one or more protons

21. BACKGROUND • These protons are very high energy and called gamma rays • Nuclei can be excited artificially by bombarding them with • Photons • Neutron • Helium nuclei

22. BACKGROUND Nuclei can also have their isotopic identification changed by bombardment and capture These changes are called isotopic transmutation and play a central role in the physics of nuclear reactors

23. BACKGROUND A chemical reaction is a reaction which involves electrons Nuclear reaction is a reaction which involves the nucleus of an atom Nuclear reactions produce more energy per atom than chemical reactions

24. BACKGROUND This is because nuclear forces holding the nucleus together are much stronger than the electrostatic forces that are holding electrons The most commonly observed from a nuclear reaction is the radioactive decay The radioactive decay causes a heavy atom to transform to a lighter atom of a different element

25. BACKGROUND For example, in the following a radioactive decay of Uranium 238 decomposes it to Thorium with the release of an alpha particle (He nuclei)

26. NUCLEAR REACTION • It is a reaction that changes the number of protons or neutrons in the nucleus of an atom • There are several kinds of nuclear reactions • Fragmentation of large nuclei into smaller ones • Nuclear fission • Building up of small nuclei into larger ones • Nuclear fusion

27. NUCLEAR FISSION • It is a nuclear reaction in which nucleus of an atom splits into smaller parts • This process often release neutrons • Self-sustaining chain reaction, if slowed (concept of “moderator” invented by Fermi) • It also releases enormous amount of energy in the form of heat

28. NUCLEAR FISSION Barium Krypton In 1939 Hahn and Strassman in Berlin bombarded a Uranium-235 isotope with neutrons and demonstrated nuclear fission for the first time

29. NUCLEAR FISSION • The naturally mined uranium contains 0.7% of U-235 and 99.3% of U-238 • Separation is difficult • Bohr found that nuclear fission was much more likely to occur in Uranium-235 isotope than in Uranium-238 • The process of “enrichment” was developed to increase concentration of U-235 in the mixture

30. NUCLEAR POWER PLANT In a nuclear power plant, a nuclear reactor produces and controls the release of energy from splitting the atoms of elements such as uranium and plutonium The energy released as heat from the continuous fission of the atoms in the fuel is used to make steam

31. NUCLEAR POWER PLANT

32. CORE Reactor core is the portion of the nuclear reactor which contains the nuclear fuel where the nuclear reaction takes place The main function of a core is to create an environment which establishes and maintains the nuclear chain reaction It provides a means for controlling the neutron population and removing the energy released within the core

33. MODERATOR Moderator is a material which slows down the released neutrons from the fission process Slow moving neutrons are much more likely to be absorbed by uranium atoms to cause fission than fast moving neutrons Newly released neutrons after a nuclear fission move at 300,000 km/sec

34. MODERATOR It must be slowed down or “moderated” to speeds of a few km/sec This is necessary to cause further fission and continue the chain reaction

35. MODERATOR • The most commonly moderators are • Water - H2O • Light water reactor • Not efficient – it slows neutrons and also absorbs them • Heavy water D2O (formed by a heavier isotope of hydrogen with atomic mass 2) • Heavy water reactor • Efficient • Graphite

36. FUEL • The most common fuel is • Uranium-235 • Plutonium-239 • Light water reactors use uranium oxide (UO2) pellets which are arranged in zirconium alloy tubes to form fuel rods (melting point of UO2 is 2800oC)

37. FUEL Pellets are 1 cm in diameter and 1.5 cm long

38. FUEL The fuel rods are placed in fuel assemblies in the reactor core

39. CONTROL ROD • It is made of neutron-absorbing material • Cadmium • Hafnium • Boron • Rods are used to control the rate of reaction • They are inserted or withdrawn from the core to decrease or increase the rate of fission

40. CONTROL ROD

41. CONTROL ROD Inserting the rod slows down the reaction by absorbing the neutrons and reducing the available neutrons for fission Withdrawing them has the opposite effect Allowing the rate of fission to grow beyond a certain point can be very dangerous (Chernobyl)

42. COOLANT It is a liquid or gas circulating around or through the core It carries the heat away from the reactor It generates steam in the steam generator The most common coolant is pressurized water

43. STEAM GENERATOR It is a heat exchanger Uses heat from the core which is transported by the coolant Produces steam for the turbine

44. CONTAINMENT It is the structure around the reactor core It protects the core from outside intrusion Protects outside environment from effects of radiation in case of a malfunction Typically it is a meter thick concrete and steel structure

45. SPENT FUEL POOL It stores the spent fuel from the nuclear reactor About 1/4 to 1/3 of the total fuel is removed from the core every 12 to 18 months and replaced with the fresh fuel The removed fuel rods still generate a lot of heat and dangerous radiation

46. SPENT FUEL POOL The fuel bundles freshly removed from the core are separated for several months for initial cooling Then they are sorted in other parts of the pool for final disposal Metal racks keep the fuel in safe positions to avoid the possibility of a nuclear chain reaction

47. SPENT FUEL POOL The spent fuel is typically stored underwater for 10 to 20 years before being sent for disposal or reprocessing

48. PRODUCTION COST OF NUCLEAR POWER