1. 4/2003 Rev 2 I.4.9f – slide 1 of 50 Session I.4.9f Part I Review of Fundamentals Module 4Sources of Radiation Session 9fFuel Cycle – Fuel Fabrication IAEA Post Graduate Educational Course Radiation Protection and Safety of Radiation Sources

2. 4/2003 Rev 2 I.4.9f – slide 2 of 50 Object is to convert enriched UF 6 into UO 2 fuel pellets, suitable for use as fuel in a reactor Fuel Fabrication

3. 4/2003 Rev 2 I.4.9f – slide 3 of 50 Fuel Fabrication Overview  Large, industrial-type facilities  Generally good construction  Confinement not containment of Special Nuclear Material (SNM)  No shielded areas  Generally operators/people involved/intertwined with the process  Low radiation and airborne hazards

4. 4/2003 Rev 2 I.4.9f – slide 4 of 50 Basic Chemical Approaches  “Wet” process chemistry  hydrolyze UF 6 in solution  precipitate with ammonia compounds  calcine/reduce to UO 2  ADU = ammonium diuranate  “Dry” process chemistry  hydrolyze UF 6 with steam  convert to UO 2 with steam/H 2  IDR = Integrated Dry Route

5. 4/2003 Rev 2 I.4.9f – slide 5 of 50 Importance of Fuel  First two layers of confinement:  Fuel form itself  (Metal) cladding  Must be high quality - “Perfect”  Leakers often require reactor shutdown  Special handling/canning of leaking spent nuclear fuel (SNF)  Money, radiation dose and waste if wrong

6. 4/2003 Rev 2 I.4.9f – slide 6 of 50 Importance of Fuel  Fuel around for “decades”  about 1 year after fabrication  usually 3 cycles (about 5 years) in reactor  minimum of 5 years in wet SNF storage  minimum of 20 years in dry SNF storage  some power reactor fuel 35+ years old  Repository - 100+ years  Fuel is the “tail that wags the dog”

7. 4/2003 Rev 2 I.4.9f – slide 7 of 50 Fuel Considerations  Enriched UF 6 not suitable for fuel  Requires chemical conversion to more stable and robust form  Requires mechanical activities, cladding, and assembly  Fuel requires high density to achieve adequate nucleonics and properties

8. 4/2003 Rev 2 I.4.9f – slide 8 of 50 Chemical Forms of Uranium Fuel  UO 2 (a compromise) is used in most power reactors (LWRs, PHWRs, AGRs, RMBKs) as cylindrical pellets  Pebble bed would use coated UO 2 and would probably be a UO 2 /UC mix

9. 4/2003 Rev 2 I.4.9f – slide 9 of 50 Nuclear Fuel Enrichment  Enrichment Levels  PWR: 2.5-4.5%  BWR: 3-5%  CANDU/PHWR: 0.71%  Naval/Research: up to 100%  Gas/graphite: 0.71-20%  FBR/LMFBR/IFR - 0.2 (blanket) to 30% (driver); 15-25% fissile (Pu) typical

10. 4/2003 Rev 2 I.4.9f – slide 10 of 50 Nuclear Fuel Core Time and Quantities  Core irradiation time, years  CANDU/PHWR: < 1  PWR/BWR: 4-5  Naval/research: 1 - 20+  Gas/graphite: 0.5-3 typical, some > 5  FBR/LMFBR/IFR: 3-5 (driver)  Physical quantities small  about 10,000 MTHM/yr world  about 2,000 MTHM/yr US  U.S. SNF about 50,000 tonnes  All U.S. SNF would fit on a football field 7.6 m deep, subcritical

11. 4/2003 Rev 2 I.4.9f – slide 11 of 50 Typical PWR Fuel Load  1,000 MWe nominal  193 assemblies  51,000 fuel rods  18,000,000 fuel pellets  Typical reject/rework rates  1-3% on pellets  0.1-0.3% on rods  very low for assemblies

12. 4/2003 Rev 2 I.4.9f – slide 12 of 50 UF 6 received from enrichment facility in cylinders Cylinders removed from package, weighed, and transferred to UF 6 storage pad UF 6 Cylinders Arriving at Facility Fuel Fabrication

13. 4/2003 Rev 2 I.4.9f – slide 13 of 50 Greatest Environmental Hazards in Fuel Fabrication  Whether wet or dry …  chemical conversion of UF 6 into UO 2  chemical operations in scrap/recovery

14. 4/2003 Rev 2 I.4.9f – slide 14 of 50 Ceramic Process and Final Fuel Fabrication  Ceramic Process  Pretreat  Pelletize (green)  Sinter  Grind  Wash/dry  Inspect

15. 4/2003 Rev 2 I.4.9f – slide 15 of 50 Sample Sintered Pellets

16. 4/2003 Rev 2 I.4.9f – slide 16 of 50 What are Burnable Poisons?  Materials in fuel that limit reactivity for part of the reactor operating cycle (absorb some neutrons)  “Poison Rod”  like a weak control rod  no fuel, just the neutron poison  “Poisoned Rod”  contains fuel and poison  poison in fuel pellets or as separate pellets in rod  Gadolinia and erbia typical poisons due to large neutron cross-sections

17. 4/2003 Rev 2 I.4.9f – slide 17 of 50 Mechanical Process Steps  Mechanical Process  Prepare rods  Load pellets  Seal rods  Make assemblies/Inspect  Store, prior to transportation

18. 4/2003 Rev 2 I.4.9f – slide 18 of 50 Why zirconium?  Capable of withstanding high T, P and radiation for years for years  Structural strength (for tubing)  Corrosion resistance in most coolant environments  Low thermal neutron absorbance  Zr 0.185 b (1 barn = 1E-24 cm 2 )  Hf 10.2 b (common impurity)  Reactor grade Zr requires < 100 ppm Hf  Alloys (mainly Zr, some Sn - 1%)  Zircaloy-2 (BWR typical)  Zircaloy-4 (PWR typical)  Others - “Zirlo”

19. 4/2003 Rev 2 I.4.9f – slide 19 of 50 Fuel Pellet “Stacks”

20. 4/2003 Rev 2 I.4.9f – slide 20 of 50 Fuel Rods

21. 4/2003 Rev 2 I.4.9f – slide 21 of 50 Spacer Grids Skeleton Assemblies BWR Grid PWR BWR

22. 4/2003 Rev 2 I.4.9f – slide 22 of 50 The completed fuel assembly is washed and inspected Fuel Assembly in Fixture Fuel Assembly Clean Check Assemblies

23. 4/2003 Rev 2 I.4.9f – slide 23 of 50 Visual Inspection PWRAssembly

24. 4/2003 Rev 2 I.4.9f – slide 24 of 50 Storage  Assemblies stored in racks to  preclude water accumulation  maintain minimal separation/distances

25. 4/2003 Rev 2 I.4.9f – slide 25 of 50 Fuel Assemblies  1,000 MWe Reactor - about 100 MTHM in core  30-34 MTHM in refueling, every 18 months  60-70 assemblies per refueling (PWR)  PWR and BWR assemblies different  BWR smaller size, weight, but about same height  BWR more void space and channels  PWR assembly about 0.5 MTHM  BWR assembly about 0.2 MTHM

26. 4/2003 Rev 2 I.4.9f – slide 26 of 50 PWR/BWR Assemblies PWR 17 x 17 BWR 9 x 9

27. 4/2003 Rev 2 I.4.9f – slide 27 of 50 Typical Scrap Materials  Off-specification pellets  Solids, residues, cleanout from processes (ADU, UOx)  Filter materials, blowback  Machined scrap - from grinding etc.  Dust from the ceramic process  hammer mills, attritors  granulating/slugging anything containing uranium even incinerator ash

28. 4/2003 Rev 2 I.4.9f – slide 28 of 50 Upon final acceptance of the fuel assembly, units are packed in shipping containers for transfer to utility power reactor site Fuel Assembly Packing Shipping Container Loading Fuel Fabrication

29. 4/2003 Rev 2 I.4.9f – slide 29 of 50 Assembled Fuel Bundle At the Nuclear Power Plant, new fuel assemblies are inspected and loaded into the reactor core where the 235 U in the fuel pellets fissions producing heat for electric power generation Fuel Fabrication

30. 4/2003 Rev 2 I.4.9f – slide 30 of 50 What is MOX?  MOX contains plutonium  Mixed uranium-plutonium OXide fuel  Can be reactor or weapons grade Pu  A one-third core approach “essentially” same as LEUO 2  Matrix is sintered DUO 2 pellets  5-8% Pu in pellets

31. 4/2003 Rev 2 I.4.9f – slide 31 of 50 Experience with MOX  European experience positive:  over 20 reactors licensed for MOX (one-third)  over 15 reactors using MOX  MOX burnup license limit: 42,000 MWD/MTHM  several fuel fabrication facilities  Melox/France is the largest - dry powder processing (about 200 MTHM/yr capacity; licensed at 105)  several minor incidents but no accidents  U.S. experience limited  test assemblies, FBR fuel  wet processing, generally OK  some contamination concerns

32. 4/2003 Rev 2 I.4.9f – slide 32 of 50 MOX Trends?  French, Swiss - continuing  Germany - “some MOX activities”  Britain - “waiting”  Japan - “planning”  Russia/FSU - valuable resource  Environmental Safety and Health impact:  low, no discernable trend  fuel fabrication doses, impact comparable to U facilities to U facilities

33. 4/2003 Rev 2 I.4.9f – slide 33 of 50 Use of Weapons Pu  Short irradiation and low burnup  Uses Pu from dismantled weapons  Typically 90%+ fissile Pu  Requires purification from Ga, Am-241 in-growth  Weapons Pu starts as metal, not as the oxide

34. 4/2003 Rev 2 I.4.9f – slide 34 of 50 ES&H Concerns  Pu and MOX powder more radiotoxic than UO 2 fuel powder  Room release example: 1 mg in nominal room, 1 minute exposure, nitrate = 0.35 Sv inhalation dose  Ground release example: at 100 meters, 0.32 g, 1 hour exposure = 1Sv (from Pu-239)  Uranium quantities would have to be 100 times larger to give the same doses  More radioactive/gamma, particularly for reactor Pu  Criticality  Once pelletized, sintered, in rods  essentially no impact

35. 4/2003 Rev 2 I.4.9f – slide 35 of 50  UF 6 release  Criticality  Chemicals used in process Fuel Fabrication Hazards