Nuclear Power: Conventional Fission, Advanced Concepts and Remarks on Fusion

1. Nuclear Power:Conventional Fission, Advanced Concepts and Remarks on Fusion

2. NUCLEAR POWER PLANT

3. The 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

4. NUCLEAR POWER PLANT

5. MODERATOR Newly released neutrons after a nuclear fission move at 300,000 km/sec “Fast neutrons” Think of the energy contained as kinetic energy E=hn=1/2mv2 Slow moving neutrons are much more likely to be absorbed by uranium atoms to cause fission than fast moving neutrons Moderator is a material which slows down the released neutrons from the fission process

6. MODERATOR Neutrons must be slowed down or “moderated” to speeds of a few km/sec “epi-thermal neutrons” • This is necessary to cause further fission and continue the chain reaction

7. Common Moderators • Water - H2O • Light water reactor • Not efficient – it slows neutrons and absorbs them • Heavy water (D2O) • Heavy water reactor • Efficient – slows neutrons and bounces them back • CANDU (Canada Deuterium Uranium) reactor can use natural/low enriched Uranium! • Graphite • RBMK design • Efficient, but graphite (carbon) can burn…

8. NUCLEAR POWER PLANT

9. Control Rods • Too many neutrons could lead to runaway reaction (not a good thing) • Number of neutrons in reactor controlled by absorbing some • Made of neutron-absorbing material • Cadmium • Hafnium • Boron Rods inserted or withdrawn from the core to control rate of reaction

10. CONTROL ROD

11. NUCLEAR POWER PLANT

12. COOLANT Liquid or gas circulating through the core Carries the heat away from the reactor It generates steam in the steam generator May not have separate steam and coolant cycles The most common coolant is pressurized water Others include Helium, CO2, molten Na/K, molten Pb/Bi, molten Na2AlF6

13. Boiling Water Reactor • 1000 psi, 285oC

14. Pressurized Water Reactor • 2300 psi, 315oC

15. CANDU-PHWR

16. Pressure Tube Graphite moderated R (PTGR) Note: this is the RBMK reactor design as made famous at Chernoybl

17. HTGR

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

19. NUCLEAR POWER PLANT

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

21. Containment Structure

22. SPENT FUEL POOL Stores the spent fuel from the nuclear reactor About ¼ of the total fuel is removed from the core every 12 to 18 months and replaced with fresh fuel Removed fuel rods still generate a heat and radiation Spent fuel kept in “pool” filled with “poisoned water” • Water that absorbs neutrons • Usually Li/B salts dissolved in water

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

24. CATEGORIES OF RADIOACTIVE WASTE Low Level Radioactive Waste Clothing used by workers, gasses and liquid emitted by reactor Hospital waste, etc Stored in metal containers on site, later permanently disposed Shallow land burial (often incinerated first) Intermediate Level Radioactive Waste Fuel element claddings, materials from reactor decomissioning Deep burial High Level Radioactive Waste Spent fuel (fission products and actinides after cooling) Remainder from reprocessing Currently disposed at WIPP

25. Problematic Waste

26. Remaining activity after storage Curie (Ci): 37,000,000,000 disintegrations per second (1 gram pure radium)

27. Nuclear Waste

28. Radiation Units Rad: radiation absorbed dose: 0.01 J / kg body tissue SI unit is Gray (1 rad = 10 mGy) US customary unit still rad Rem: roentgen equivalent manThe dose equivalent in rems is numerically equal to the absorbed dose in rads multiplied by modifying factors for each radiation type. Alpha: 1/10 Beta: 1 Gamma: 1 SI unit is Sievert (Sv, 100rem = 1 Sv)

29. Exposure levels • 500 rem dose fatal to 1/2 of population • 100 - 200 rem: vomiting, temporary sterility, hair loss, spontaneous abortion, cancer • 5 rem: maximum allowable sustained exposure • AY dosimeters from XRD: never greater than 0.5 rem

30. Exposure Pathways

31. Effects of Ionizing Radiation Ionizing radiation has sufficient energy to knock bound electrons from atom or molecule Can form highly reactive free radicals with unpaired electrons E.g., H2O  [H2O.] + e- Rapidly dividing cells are particularly susceptible to damage • Pregnancy… • Used to treat certain cancers Chemistry in Context, Chapter 7

32. Natural sources (81%) include radon (55%), external (cosmic, terrestrial), and internal (K-40, C-14, etc.) • Man-made sources (19%) include medical (diagnostic x-rays- 11%, nuclear medicine- 4%), consumer products, and other (fallout, power plants, air travel, occupational, etc.) http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs10bkvsman.htm NCRP Report No. 93 www.epa.gov/rpdweb00/docs/402-f-06-061.pdf

33. www.epa.gov/rpdweb00/docs/402-k-07-006.pdf

34. Effect of Smoking on Radiation Dose Average annual whole body radiation dose is about 360 mrem If you smoke, add about 280 mrem Tobacco contains Pb-210 from fertilizer Decays to Po-210. Pb-210 deposits in bones. Po-210 works on liver, spleen, kidneys http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs10bkvsman.htm http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm

35. Waste… • Fuel reprocessing… • Geological repositories • Identify solutions that are both safe and publicly acceptable • Use retrievable form, rather than irreversible solution • Allow adoption a better solution in future • Sweden – site selection for nuclear waste repository • Finland • Proposal to build repository in cavern near the NPPs at Olkiluoto. • Construction start in 2010, operation about 2020 (parliament approval?) • “Yucca Mountain” • Other R&D • reduce actinide generation • transmutation using accelerator driven system • Change long-lived nuclear waste to low or medium nuclear waste

36. WIPP? “Waste Isolation Pilot Plant” Waste from research and weapons programs Open in 1999

37. Transmutation? Isn’t that what alchemists do? This is where Actinides (IUPAC: “actinoids”) come from Example:

38. Transmutation 238U can be made into fissile 239Pu 232Th can be transmuted to 233U • Fertile material: can be transmuted to fissile material • After 5 years in fast breeder reactor can get enough 239Pu to fuel another reactor from 238U… • Natural U is 99.3% 238U… • Similar for 232Th, also there’s 4x as much Th as U in the world… • Fissile material: actual nuclear fuel

39. Waste Fuel Reprocessing UREX process (URanium EXtraction) Dissolve waste fuel in HNO3 Extract with tributylphosphate/alkane mixture Crash out recovered U using reductant (e.g., NaBH4) AY worked on e-chem variant of this (used depleted 238U…) PUREX is a variant – also extracts Pu Remaining aqueous stuff has actinides, fission products Dispose by vitrification/synroc

40. Future Reactor Designs Research is currently being conducted for design of the next generation of nuclear reactor designs. The next generation designs focus on: • Proliferation resistance of fuel • Passive safety systems • Improved fuel efficiency (includes breeding) • Minimizing nuclear waste • Improved plant efficiency (e.g., Brayton/combined cycle) • Hydrogen production • Economics

41. Future Reactor Designs (cont.)

42. Design improvements (Generation III Designs) • New thermal management systems • Advanced Boiling Water/Pressurized Water • Light water reactors (LWRs) • Heavy water reactors (HWRs) • Gas cooled reactors • Liquid metal cooled • Improved core designs • Pebble bed modular reactor (110 MWe reactor at ca. $1k/kW) • Sub-critical hybrid systems • Improved Safety • Passive thermal management if failure • Waste management…

43. Pebble Bed Reactor No control rods needed Intrinsically safe fuel elements He cooled Use of Th fuel cycle

44. Pebble Bed Fuel Elements

45. Advanced Boiling Water Reactor (ABWR) More compact design: cuts construction costs increases safety Additional control rod power supply improves reliability Designed for ease of maintenance Two built and operating in Japan

49. Generation IV Concepts • Very High Temperature Reactor (VHTR) • Supercritical Water-Cooled Reactor (SCWR) • Lead-Cooled Fast Reactor (LFR) • Molten Salt Reactor (MSR) • Sodium-Cooled Fast Reactor (SFR)

50. Very High Temperature Reactor (VHTR) Thermal neutron spectrum Helium-cooled core (1000oC+) Potential H2 production