Preliminary Results of the AGC-3 Irradiation in the Advanced Test Reactor and Design of AGC-4

1. Preliminary Results of the AGC-3 Irradiation in the Advanced Test Reactor and Design of AGC-4 Proceedings of the 2014 15th International Nuclear Graphite Specialists Meeting INGSM-15 September 15– September 18, 2014, Hangzhou, China

2. Agenda • Graphite irradiation overview • ATR irradiation locations & details • Graphite specimens • Capsule & test train design • Control & monitoring systems • AGC-3 Experiment • Irradiation • AGC-4 Experiment • Design • Summary ATR Core During Reactor Operation

3. Graphite material property database • Irradiation creep • Thermal changes • Mechanical changes • Physical changes Graphite Irradiation Experiments • Historic nuclear grade graphites are no longer available due to loss of feedstock • ATR experiments to be irradiated: • 600, 800 & 1100ºC • Up to 4 or 7 dpa (5.5 and 9.6 x 1021 n/cm2 for E > 0.1 MeV) • AGC-1 was irradiated from September 2009 to January 2011 • AGC-2 was irradiated from April 2011 to May 2012 • AGC-3 was irradiated from November 2012 to April 2014 • AGC-4 will be irradiated from February 2014 to January 2017 1500 ºC HTV-1 HTV-2 AGC - 5 AGC - 6 1100 ºC 800 ºC AGC - 3 AGC - 4 High dose tensile irradiation creep studies needed for pebble bed design 600 ºC AGC - 1 AGC - 2 Database for previous nuclear graphite grades 4.5 1 3 6 Dose (dpa)

4. AGC Experiment Locations North • AGC-1 & AGC-2 were irradiated in the South Flux Trap position • AGC-3 & AGC-4 being irradiated in the East Flux Trap of the ATR • Use of ATR Flux Trap • Maximizes number of graphite specimens, stacks/channels, loads, and combinations • Flux rate minimizes irradiation time to meet NGNP program schedule • Test trains rotated to minimize flux gradient across diameter • Most of ATR core height (44” of 48”) used to maximize specimen numbers and provide spectrum of fast fluence damage levels Fuel Elements H Positions Small B Position East Flux Trap Location for AGC-3 & 4 South Flux Trap Location for AGC-1 & 2 Control Drum I Positions ATR Core Cross Section

5. Unloaded Small Specimens Core Centerline Compressive Load Push Rod Loaded Large Specimens Full Size Unloaded Specimens AGC-3 Graphite Specimens • Same large & small specimens • Large - Ø ½” (12.3 mm) × 1” (25.4 mm) tall • Small - Ø ½” (12.3 mm) × ¼” (6.4 mm) tall • New ‘intermediate’ size specimen container • Ø ½” (12.3 mm) × ½” (12.7 mm) tall • 6 Perimeter Stacks • 18 large size specimens above core center • 18 large and 3 small size specimens below core center • Center Stack • 152 small and 9 intermediate size specimens • Flux wires in spacers between graphite specimens Small Specimen Large Specimen Spacer Flux Monitor AGC-3 Specimen Stack

6. AGC Experiment ATR Top Head AGC Being Inserted into the ATR AGC-3 Irradiation Requirements • 800ºC design temperature • Fast neutron damage up to 3 to 4dpa • Compressive loads on specimens • 2 stacks with 2 ksi (14 MPa) compressive load • 2 stacks with 2.5 ksi (17 MPa) compressive load • 2 stacks with 3 ksi (21 MPa) compressive load • Loaded and unloaded companion specimens • Lift specimens during reactor outages to verify specimen load condition • Grab samples of temperature control gas to monitor for oxidation of specimens

7. Specimen Holder Thermocouples Lower Bellows Gas Line Temperature Control Gas Line Heat Shield/Gas Jacket Area Graphite Specimens AGC Capsule Cross Section AGC Capsule Design Features • 6 specimen stacks around capsule perimeter with compressive load on upper half of stack • 7th specimen stack in center without compressive load • Graphite holder to contain graphite specimen stacks and thermocouples (TCs) • 12 TC locations with positions located throughout core height • Insulating gas jacket to attain desired temperature • Radiation heat shield to limit radiation heat transfer

8. Temperature Control • Utilize neutron capture and gamma heating of specimens as heat source • Manipulate temperature by adjusting ratio of conducting and insulating gases in insulating gas gap • AGC irradiations use He and Ar to maximize control band for temperature control • All AGC experiments utilize same temperature control system • Distributed control system used for control and data collection

9. Position Indicators Graphite Specimens Pneumatic Ram Load Cell Push Bar Push Rod Gas Bellows Compressive Load System • Pneumatic rams provide compressive load on specimens in six peripheral stacks located above the ATR core centerline – no load on specimens below core centerline • Load cells between pneumatic rams and push bars to monitor specimen load • Push bars translate and transmit compressive load to push rods located in smaller circle directly over specimen stacks • Stainless steel push rods transition to graphite in higher temperature areas of experiment • Gas bellows below core to lift top specimens during outages to verify load conditions • Position indicators attached to push bars to verify specimen movement during outages • Compressive loads imposed on diametrically opposite specimen stack pairs to avoid eccentrically loading the graphite holder AGC Test Train

10. AGC-2 Design Changes/Improvements • TC12 moved to same elevation as TC9 to provide temperature gradient across the whole experiment • Replaced stainless steel with aluminum in some internal components to reduce weight • Load cell adapter, plates, push bars and sleeves • Tungsten ‘gamma heaters’ added to top and bottom of center channel • Zirconia gamma heaters added to the bottom of peripheral channels • Removed spacers in specimen stacks to increase number of specimens • 36 large and 14 to 18 small specimens in peripheral stacks (vs. 29 and 14) • 170 (vs. 172) small specimens in center stack due to tungsten heaters TC Locations TC Pair Locations in AGC-2

11. Specimen Holder Thermocouples Lower Bellows Gas Line Temperature Control Gas Line Heat Shield/Gas Jacket Area Graphite Specimens AGC Capsule Cross Section AGC-3 Design Challenges and Changes • East Flux Trap vs. South Flux Trap • 15% lower nominal power • 20% power variation versus 10% for AGC-1 & AGC-2 • Increased specimen creep from higher design temperature (800ºC) • Slightly smaller diameter specimens • Additional stroke in pneumatic cylinders • Additional room at core center for creep in specimens & housing • Elevated mean wall temperature in pressure boundary from higher temperature • Five versus single vertical temperature control zone • Significantly enhanced temperature control • Significantly improved axial temperature distribution • Different gamma ‘heaters’ • Molybdenum vs. tungsten & zirconia

12. AGC-3 & 4 Schedule & Status • AGC-3 Status • Start of irradiation - November 2012 • Moisture level during start-up • Excellent temperature control • Extremely flat axial temperature profile • Compressive load control system leakage • Helium shortage • Loads reduced on stacks 2 & 5 to replace/supplement stacks 1 & 4 • Completed Irradiation- April 2014 • Accumulated 210 EFPDs • Peak fast neutron damage – 3.63 dpa • AGC-4 Status • Completed final design July 2014 • Assembly expected to complete November 2014 • Irradiation expected to begin February 2015 Gas Bellows before installation in outer shell Outer shell with gas bellows installed inside Lower Gas Bellows installed on test train

13. AGC-3 Temperatures During Irradiation

14. AGC-3 Compressive Loads During Irradiation

15. AGC Connections to Control Systems ATR Flux Trap Top Head Penetration AGC Test Train ATR Vessel ATR Core ATR Fuel Summary AGC-3 Experiment • Multiple design improvements and lessons learned from AGC-1 & AGC-2 incorporated • New design challenges from increased temperature & new irradiation position • Irradiation started in November 2012 • Significant improvement in temperature control & axial temperature profile • Compressive load control system leakage • Accumulated 210 EFPDs • Peak fast neutron damage level – 3.63 dpa • Irradiation completed in April 2014 • Sizing and Shipping for PIE expected November 2014 AGC-4 irradiation expected to commence early 2015 AGC Experiment Installed in ATR