1. Document : n.a.Proprietary Class 3Page 1 The design of the PBMR Core Structures Mark Mitchell Pebble Bed Modular Reactor (Pty) ltd. Fifth International Nuclear Graphite Specialists Meeting Plas Tan-Y-Bwlch, Maentwrog, Gwynedd, United Kingdom 12th – 15th September, 2004

2. Document : n.a.Proprietary Class 3Page 2 Content Overview of the PBMR Plant design Overview of the PBMR Reactor Unit Description of the design of the PBMR Core Structures –Core Barrel Assembly (CBA) –Core Structures Ceramics (CSC) Current status of the project

3. Document : n.a.Proprietary Class 3Page 3 PBMR Plant Design Overview The PBMR Main Power System (MPS), end 2003. Reactor Unit HPTLPT PTG Recuperator Pre-cooler Inter-cooler CBCS CCS

4. Document : n.a.Proprietary Class 3Page 4 Reactor Core Barrel Conditioning System Maintenance Isolation/Shutdown Valve Generator Power Turbine Recuperator High Pressure Compressor Low Pressure Compressor Gearbox Inter-Cooler Core Conditioning System Pre-Cooler Main Power System - 2004

5. Document : n.a.Proprietary Class 3Page 5 Brayton Cycle (PFD)

6. Document : n.a.Proprietary Class 3Page 6 Main Power System T-S Diagram (HTR and VHTR)

7. Document : n.a.Proprietary Class 3Page 7 Main Power System in Building

8. Document : n.a.Proprietary Class 3Page 8 RU Layout SystemFunction Core Structures (CS)To form and maintain the core geometry. Reactor Pressure Vessel (RPV) To contain the helium under pressure. Reactivity Control System (RCS) To control reactivity and shutdown the reactor Reserve Shutdown System (RSS) To shutdown the reactor Core Unloading Device (CUD) Remove the fuel elements from the core

9. Document : n.a.Proprietary Class 3Page 9 RU Vertical Section SystemFunction Fuel LineTo feed fuel spheres to the core Fuel CoreThe generate heat by nuclear fission Bottom, Centre, Side & Top Reflector To reflect neutrons back to the core Control Rod (RCS)To control the reactivity SAS Channel (RSS0To shutdown the reactor SAS Extraction PointTo extract the SAS from the SAS Channel

10. Document : n.a.Proprietary Class 3Page 10 RU Horizontal Section

11. Document : n.a.Proprietary Class 3Page 11 Core Structures – Product Breakdown Structure Core Structures (CS) –Core Barrel Assembly (CBA) Core Barrel Top Plate Upper and Lower Support Rings Upper and Lower Lateral Guides –Core Structures Ceramics (CSC) Top Reflector Side Reflector Central Reflector Bottom Reflector Lateral Restraints

12. Document : n.a.Proprietary Class 3Page 12 General arrangement of the CS. Identification of the major components of the CS.

13. Document : n.a.Proprietary Class 3Page 13 Functions of Core Structures Provide and maintain core geometry Provide and maintain flow path for fuel spheres Provide and maintain openings for the Reactivity Control and Shutdown Systems Provide inlet and outlet flow paths for helium gas Provide neutron reflection Provide thermal neutron and gamma shielding Provide and maintain specified heat transfer path

14. Document : n.a.Proprietary Class 3Page 14 Core Barrel Assembly Core barrel assembly supports the CSC Provides thermal shielding to the RPV A Schematic representation of the CBS is provided in the sketch.

15. Document : n.a.Proprietary Class 3Page 15 Core Barrel Support Philosophy Core barrel >22 m long and >18 m circumference Heats up to ~ 400°C and cools down during shutdown Uneven temperature distribution will cause barrel to bow Support design must allow for small amount of bowing Solution is the single vertical support system, coupled with lateral and seismic restraints.

16. Document : n.a.Proprietary Class 3Page 16 Layout of Core Barrel Assembly

17. Document : n.a.Proprietary Class 3Page 17 Core Structures Ceramics (CSC) Top Reflector Side Reflector Central Reflector Bottom Reflector Lateral Restraints Materials selection and environmental conditions Description of components

18. Document : n.a.Proprietary Class 3Page 18 General arrangement of the CS. Identification of the major components of the CS.

19. Document : n.a.Proprietary Class 3Page 19 Fundamental Safety Functions - CSC Safety Functions: Control reactivity (Core geometry / Control and Shutdown element access) Remove core heat (Limiting case -> Passive heat removal through core components) Contain radioactive materials (No functions associated with this.)

20. Document : n.a.Proprietary Class 3Page 20 Design Lifetime Requirements Plant Design life: –40 Calendar years –36 Full Power Years CSC Design life (Replaceable components) –Target lifetime - 24 Full Power Years –Minimum lifetime – 18 Full Power Years.

21. Document : n.a.Proprietary Class 3Page 21 Core Structures Materials Candidate materials: –Graphite NBG-10 NBG-12 NBG-32 NBG-18 –CMC’s (specifically C- C) SIGRABOND 1501 YR SIGRABOND 2001 YR –Insulation Carbon Fused quartz Alumina

22. Document : n.a.Proprietary Class 3Page 22 Graphite Materials Breakdown Grade NBG-10:Medium grain, isotropic pitch coke, extruded Locations used:- Contact areas between reflector & fuel sphere - High flux regions, typically > 10 12 n/cm 2 EDNF - Long-life components - Highly stressed & critical components Grade NBG-12:Medium grain, isotropic pitch coke, extruded (includes recycled graphite in mix) Locations used:Mainly NBG-10 replacement (larger blocks possible) Grade NBG-32:Medium grain, isotropic pitch coke (coke differs from NBG-10/12), vibration moulded Locations used:Base & top of centre reflector, larger components possible

23. Document : n.a.Proprietary Class 3Page 23 Material Exposure Conditions (HTR) ComponentMaterialTemperature (ºC)Fluence (x10 20 n/cm 2 EDN) NormalAccident Outer Central Reflector NBG-10500-10501600280 Side Reflector NBG-12500-9001200220 Tie Rods 1501YR5001000<10 20 Restraint Straps 2001YR500700<10 20 Bottom Insulation Ceramic/ Carbon 550 <10 20

24. Document : n.a.Proprietary Class 3Page 24 Scope of Graphite Irradiation Tests Selected irradiation dose and temperature range cover property changes well in excess of expected limits for the extreme surfaces of the inner side and outer central reflector up to 24 FPY. This irradiation regime also covers the expected EOL property changes for the graphite materials.

25. Document : n.a.Proprietary Class 3Page 25 General arrangement of the CS. Identification of the major components of the CS.

26. Document : n.a.Proprietary Class 3Page 26 BR (1)

27. Document : n.a.Proprietary Class 3Page 27 BR (2)

28. Document : n.a.Proprietary Class 3Page 28 BR (3)

29. Document : n.a.Proprietary Class 3Page 29 Bottom Reflector Outlet Flow Design Sections

30. Document : n.a.Proprietary Class 3Page 30 Section Through Side Reflector

31. Document : n.a.Proprietary Class 3Page 31 Typical Inner Side Reflector Block

32. Document : n.a.Proprietary Class 3Page 32 Typical Outer Side Reflector Block

33. Document : n.a.Proprietary Class 3Page 33 Central Reflector The solid central reflector allows for insertion of shutdown elements Decreases the amount of bypass flow Outer diameter is 2 m –Outer 400 mm thickness is affected by irradiation induced damage –Inner 1.2 m diameter is used as the primary load bearing structure The central reflector is supported on the core barrel bottom plate It is built up in two parts: - Structural spine interlocking cross - Vertically separated by spacer blocks to maintain single column principle Spine locked together by set of corner blocks Corner blocks also hold final side blocks in place

34. Document : n.a.Proprietary Class 3Page 34 Central Reflector Build Up (Cross Block)

35. Document : n.a.Proprietary Class 3Page 35 Central Reflector Build Up (Cross and Spacer Blocks)

36. Document : n.a.Proprietary Class 3Page 36 Central Reflector Build Up (Cross and Spacer Blocks)

37. Document : n.a.Proprietary Class 3Page 37 Central Reflector Build Up(Cross Spacer and Corner Blocks)

38. Document : n.a.Proprietary Class 3Page 38 Central Reflector Build Up (Cross and Spacer Blocks)

39. Document : n.a.Proprietary Class 3Page 39 Principles behind the TR layout The principle layout of the Top reflector.

40. Document : n.a.Proprietary Class 3Page 40 Core Lateral and Seismic Restraints The individual columns of outer side reflector supported by closed rings Two materials SS-316 L and CFRC are used in the construction to compensate for differential thermal expansion between CB and CSC Allow for small vertical movements between columns by means of sliding and not allowing relative movements of individual columns due to temperature differences. Reduce formation of gaps and reduces leakage flow Reduces the breathing loads during thermal cycling Protrusions from the metallic portions provide for connection between the CSC and core barrel during a seismic event.

41. Document : n.a.Proprietary Class 3Page 41 Lateral and Seismic Restraint Design

42. Document : n.a.Proprietary Class 3Page 42 THE RSA PROJECT RELEASE STATUS The South Africa government has designated PBMR a National Strategic Project; Project being restructured; Approach to Key Licensing Issues agreed by December 2004; Safety Analysis Report, Rev. 2 being prepared in format of Reg. Guide 1.70 with a target date of January 2006 for handover to the Regulator; Appeals to Environmental Impact Assessment positive Record of Decision being dispositioned (December 2004)

43. Document : n.a.Proprietary Class 3Page 43 THE RSA PROJECT RELEASE STATUS Site preparation to start in the second quarter of 2007; Construction to start in April 2007 Required to meet 2010 first fuel load date.