1. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. General Features 4. Commercial Reactors 5. Nuclear Reactor Safety 6. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

2. Source: IEA (2007)

5. Delivery Construction times for nuclear plants – Global average 66 months in mid-1970s 116 months (nearly 10y) in late 1990s 82 months (nearly 7y) during 2001-05

6. Energy Estimate the energy released by the fission of 1.0 kg of 235 U. (3.15e-11 J) 1000 g = 8.06e13 J (per kg). Discussion This is a large amount of energy, and it is equivalent to the energy produced by burning tones of coal or oil. 1 mol 235 g 6.023e23 1 mol 235 U 92  142 Nd 60 + 90 Zr 40 + 3 n + Q Q = (235.043924 - 141.907719 - 89.904703 - 3x1.008665) = 0.205503 amu ( 931.4812 MeV / 1 amu ) = 191.4 MeV per fission( 1.6022e-13 J / 1 MeV ) = 3.15e-11 J This amount of energy is equivalent to 2.2×10 10 kilowatt-hour, or 22 giga-watt- hour. This amount of energy keeps a 100-watt light bulb lit for 25,000 years. 2. Characteristics of Fission

7. 7 Fission Energy Budget Kinetic energy of fission fragments Prompt (< 10 –6 s) gamma (  ) ray energy Kinetic energy of fission neutrons Gamma (  ) ray energy from fission products Beta (  ) decay energy of fission products Energy as antineutrinos ( v e ) 168 MeV 7 5 7 8 12 Energy (MeV) distribution in fission reactions

8. Fission neutron energy spectrum

9. The total and fission cross section for 235 U based on NJOY-processed ENDF/B (version V) data. Neutron interactions

10. The fast fission cross section for three fissionable uranium isotopes based on NJOY processed ENDF/B (version V) data

11. The Cyclotron and Fission Research 7 Li (p, n) 7 Be 3 T (p, n) 3 He 1 H (t, n) 3 He 2 D (d, n) 3 He 2 D (t, n) 4 He 3 T (d, n) 4 He Fusion reactions studied using the cyclotron

12. 12 The Cyclotron and Fission Research Threshold* Energy range (keV) Reactionenergy(keV) narrow-energy neutron 51 V (p, n) 51 Cr2909 5.6-52 45 Sc (p, n) 45 Ti1564 2.36-786 57 Fe (p, n) 57 Co1648 2-1425 __________________________________ * The threshold energy is the minimum energy of proton required for the reaction. Neutrons of desirable energy is required for fission research.

13. Nuclear Fission13 The Cyclotron and Fission Research For neutron sources from the cyclotron, energy can be varied. Energy dependence of neutron induced fission studied. The cross section data enabled nuclear reactor design. fast neutrons - 10 MeV to 10 KeV) slow neutrons - 0.03 to 0.001 eV for neutron induced fission

14. Nuclear Fission 14 Fission Products nuclides produced in nuclear fission Data on fission products are required for reactor design, operation, and accident responses. The study of fission products requires the separation, identification, and quantitative determination of various elements and isotopes. Fission products emit  particles until they are stable, n also. Mass number range: 40 - 170 Elements range: all the elements in the 4 th, 5 th, and 6 th periods. including the lanthanides. 2. Characteristics of Fission

15. Nuclear Fission 15 Fission Products Fission yield is the relative amounts of nuclides formed in fission reactions. The fission yield curve shown here shows most fission reactions split fission atoms into two unequal fragments.

16. Nuclear Fission Products Fission-product and their decay data are needed for social and environmental concerns, and for the management of used fuel. Fission nuclides usually have very short half lives. Typical medium-life fission products: 85 K 10.7 y, 90 Sr 29 y, 137 Cs 30 y, Typical long-life fission products: 126 Sn 1.0e5 y, 126 Tc 2.1e5 y, 91 Tc 1.9e6 y, 135 Cs 3.0e6 y, 107 Pd 6.5e6 y, and 129 Tc 1.6e7 y. Xenon poisoning: 115 Xe,  c = 2,640,000 b, and t 1/2 = 9.2 h

17. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. General Features 4. Commercial Reactors 5. Nuclear Reactor Safety 6. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

18. Simplified schematic layout of a typical reactor power plant. 3.1 A nuclear power plant

19. Control rods, containing neutron-absorbing elements (boron or cadmium) pressure vessels must be capable of withstanding internal pressures up to 160 bar. A biological shield, normally several feet of concrete, surrounds the entire system. Its purpose is to attenuate the intensity and neutron radiations to levels that are safe for humans outside the plant The coolant is pumped through the core inside the pressure vessel and through heat exchangers outside, where steam is generated and used to drive turbines for generating electric power. The melting point of uranium is 1403 K, The melting point of UO 2 is 3138 K

20. fastabso rp. 3.2 The neutron cycle

21. subcritical supercritical self-sustainingcritical

22. 3.3 Moderator Properties of materials used as moderators

23. 3.4 Optimizing the design f is a decreasing function and p an increasing function of moderator-to-fuel ratio N M / N F Uranium ~ graphite assemblies

24. Diffusion length the root-mean-square distance a neutron will diffuse in the medium before being absorbed Diffusion and slowing-down constants for moderators.

25. R, The reaction probability per unit time for N nuclei; M is the mass of fissile material if each fission liberates an amount E of recoverable energy, the power output is Reactor power and fuel consumption

26. example calculate the power output, rating and fuel consumption for a thermal reactor containing 150 tonnes of natural uranium operating with a neutron flux of energy per fission E = 200 MeV

27. Fuel consumption, leading to a loss of 235 U, depends on the total 235 U absorption cross section = 5.9 x 10 26 /year one-fifth of the initial amount of 235 U refueling

28. 5.2 Reactor Kinetics A Simple Reactor Kinetics Model Consider a core in which the neutron cycle takes l' seconds to complete The change Δn in the total number of thermal neutrons in one cycle at time t or

29. =1.001 Uncontrollable !

30. Revised Simplified Reactor Kinetics Models Consider a thermal reactor fueled with 235 U The average or effective generation time required for all the neutrons produced in a single neutron cycle is thus Delayed neutron average lifetime is A fraction β of the fission neutrons requires a cycle time of while a fraction (1 -β) is the prompt-neutron fraction and requires a cycle time of only =0.083 s

31. -> 0.083 s controllable !

32. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. General Features 4. Commercial Reactors 5. Nuclear Reactor Safety 6. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

33. Key Reactor Power Terms Availability – Fraction of time over a reporting period that the plant is operational – If a reactor is down for maintenance 1 week and refueling ( 补给燃料） 2 weeks every year, the availability factor of the reactor would be (365-3 * 7) / 365 = 0.94

34. Key Reactor Power Terms Capacity – Fraction of total electric power that could be produced – If reactor with a maximum thermal power rating of 1000 MWt only operates at 900 MWt, the capacity factor would be 0.90 Efficiency – Electrical energy output per thermal energy output of the reactor Eff=W/Q R (MWe/MWt) ~33% Carnot efficiency,

35. 4. Commercial Reactors Piecing Together a Reactor 1. Fuel 2. Moderator 3. Control Rods 4. Coolant 5. Steam Generator 6. Turbine/Generator 7. Pumps 8. Heat Exchanger Simplified schematic layout of a typical reactor power plant

36. Basic Diagram of a PWR (Pressurized Water Reactor) http://www.nrc.gov/ two water loops: The water in the primary loop is pumped through the reactor to remove the thermal energy. The loop 2, water is converted to high temperature and high pressure steam that turns the turbo-generator unit.

37. The great disadvantage of water as a coolant: must remain in liquid form, steam is a much poorer coolant than liquid water. must be pressurized to prevent boiling at high temperatures (15.5 MPa). For water, the critical temperature is 375 °C, above which liquid water cannot exist. Typically, coolant temperatures are limited to about 340 °C.

38. The steam cycle of a pressurized water reactor. [Westinghouse Electric Corp.

39. It is about 13 meters tall with a diameter of about 4 to 6 m. The vessel is built from low-alloy carbon steel and has a wall thickness of about 23 cm The primary coolant enters the vessel through two or more inlet nozzles, flows downward between the vessel and core barrel

40. Parameters for a typical 1000 MW(e) PWR sold in the early 1970s.

41. Boiling-water reactor a pressurized-water reactora direct-cycle, boiling-water reactor water is allowed to boil self-stabilizing behaviour

42. Breeder Reactor 增值反应堆 The uranium cycle breeder reactors require fast neutrons. Liquid metal and steam may be used as coolants for fast breeding

43. CANDU reactor

44. Reactor Generations Gen I – Prototypes in 50’s & 60’s Gen II – 70’s & 80’s – Today’s Operational Reactors – BWR, PWR, CANDU, … Gen III – ABWR, APWR – Approved 90’s – Some Built around the World Gen III+ – Current Advanced Designs in the Approval Process – Pebble Bed Reactor Gen IV – Deploy in 2030 – Economical – Safe – Minimize Waste – Reduce Proliferation

45. World Nuclear Power 443 Nuclear Reactors in 30 Countries in Operation, January 2006 Provided ~16% World Production of Energy in 2003 24 Nuclear Power Plants under Construction http://www.insc.anl.gov

46. Alternatives Renewable energy – Wind – Bioenergy – Solar – Hydro – Wave – Tidal – Geothermal Energy efficiency – Combined heat & power (CHP) – Building insulation – Efficient lighting – Efficient appliances – Efficient vehicles Controlling demand –Behaviour change Carbon capture and storage –‘burial’ of carbon from fossil fuels

47. Source: IEA (2001)

48. Alternatives Renewable energy –Wind –Bioenergy –Solar –Hydro –Wave –Tidal –Geothermal Energy efficiency –Combined heat & power (CHP) –Building insulation –Efficient lighting –Efficient appliances –Efficient vehicles Controlling demand –Behaviour change Carbon capture and storage –‘burial’ of carbon from fossil fuels

50. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. General features 4. Commercial Reactors 5. Nuclear Reactor Safety 6. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

53. What is the Public Hazard? chemical? biological? physical? radiological? psychological? Chlorine for water treatment None Nuclear explosion impossible Small risk of delayed effects, very small risk of prompt Chernobyl, Fukushima, nuclear tests

54. What Is the Goal of Reactor Safety? To prevent prompt effects with a high degree of assurance and minimize the risk of delayed effects Typically frequency of a large release < 10 -6 per reactor-year frequency of a core melt (intact containment) < 10 -5 per year

61. Careful, cautious, scrupulous!

62. 8. Nuclear Reactor Accidents

63. Safety Public remains wary of nuclear power due to Chernobyl and three mile island accidents Nuclear plants vulnerable to terrorist attacks Safer, more efficient, and more secure plants planned for the future

64. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. The Chain Reaction in a Thermal Fission 4. The Finite Reactor 5. Reactor Operation 6. Commercial Reactors 7. Nuclear Reactor Safety 8. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

65. Three Mile Isle

66. March 28, 1979, 4:00 am Secondary cooling loop stops pumping. Rising temperatures caused emergency valve to open to release pressure, but indicator light malfunctioned Due to loss of steam, water level drops, water overheats and burns out pump Reactor core overheats and begins to melt (a “meltdown”)

67. March 28, 1979, 6:30 am Overheated water contains 350 times normal level of melted down radioactive matter A worker sees the open valve and closes it To prevent an explosion, he reopens it, releasing radioactive steam into the atmosphere

68. March 28, 1979, 8:00 am Nuclear Regulatory commission is notified White House is notified TMI is evacuated All small children and pregnant women within a five mile radius are evacuated A fifteen-year clean up project awaits

69. No Nukes Words: Pat DeCou, Music: Tex LaMountain, ©1977, ASCAP Look across the sky from your home, Can you see the tower blinking while you sit a spell at home? Can you see the branches growing? Can you feel the awesome power? Can you sense its evil purpose and its doom? It grows in ways we all can understand, And its limbs are spreading all across the land. The leaves they look like dollars and the sap it ain’t so sweet. It rests upon the profits hungry people cannot eat. With promises of quiet, comfort, and peace, The hanging tree can lure to its side. But the darkness of its shadow gives us warning of the greed That tries to sell us more electric power than we need. No nukes for me, ‘cause I want my air to be Free from radiation poison falling over me. These reactors that they’re building are a giant hanging tree. Don’t you build a hanging tree over me. People soon will stop this money tree, And we’ll stop its hangin’ people, you and me. And as we struggle all together all the powers that be will go down with their own hanging tree. And out of this struggle we can plant a seedling tree, A tree that lets the sunlight share its space. A tree in tune with living, whose branches lift the soul, When you’re watching from a distance and you’re sitting all alone.

70. Uranium Mining There are three main methods: Underground mining Open pit mining In Situ Leaching (ISL)

71. Underground Mining The Case of the Olympic Dam Mine

72. Olympic Dam mine is located in South Australia Most of the mine’s profit actually comes from the copper that they mine as well Tunnels are dug into the earth, where ore is extracted The ore is crushed into a powder, then soaked in a lake. The impurities precipitate and the rest is dried by heat.

73. Ya Got Trouble…. Lake uses an intense amount of water Rabbit popluation has crashed as a result of drinking from the lake The Western Mining Corporation (WMC) is owned by BP

74. In Situ Leaching ( 现场浸取） Wells are drilled into aquifers （蓄水层）, the water is removed, and a solvent, such as hydrogen peroxide （过氧化氢）, is pumped in The peroxide dissolves the uranium, and the solution is pumped back up An ion exchange system causes the uranium to precipitate （沉淀） in the form of UO 4 2H 2 O (uranium peroxide)

75. In Situ Leaching

76. ISL has its woes Ground water supply has radioactive residues There are ISL mines in Texas, Wyoming, and Nebraska that share the same aquifers as residents

77. Chapter 4. Power From Fission 1.Introduction 2.Characteristics of Fission 3. General Features 4. Commercial Reactors 5. Nuclear Reactor Safety 6. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products