Heat Source Grade Pu238 Lessons Learned Britt Edquist
Heat Source Grade Pu-238 - Lessons Learned Britt Edquist Radiation Protection Technical & Regulatory Advisor Idaho Cleanup Project DOE EFCOG, Radiation Protection Subgroup – Washington DC – October 25, 2017
Outline u Challenging waste u Waste streams u Alpha decay impacts u Lessons learned u Repackaging at Idaho Cleanup Project (ICP) FLUOR IDAHO PROPRIETARY INFORMATION 2
Mound Boxes u Waste contaminated with heat source grade plutonium u Oversized fiberglass reinforced plywood boxes • Cannot RTR u Primarily hoods & gloveboxes • Ducting, ladders, mob buckets, hoses, assorted trash, conduit, carts, etc. u Packaged from 1979 -1982 u Grams Pu-238 per box up to 38. 8 g • Phase I boxes: 0. 005 g – 6. 373 g (108. 98 Ci) FLUOR IDAHO PROPRIETARY INFORMATION 3
Plutonium Grades Nuclide Approximate Activity Percentage Pu-238 Pu-239 Heat Source 99. 6 0. 04 Weapons 1. 77 12. 08 Pu-240 Pu-241 Pu-242 0. 01 0. 39 < 0. 001 2. 87 83. 28 < 0. 001 Am-241 Reactor AGED Weapons 2. 17 0. 4 -1. 5 150. 31 - 35 30. 47 -8 597. 05 - 10 <0. 002 0. 001 50 - 70 FLUOR IDAHO PROPRIETARY INFORMATION 4
Differences between Pu-238 and Pu-239 Pu-238 87. 75 17. 1 Alpha Pu-239 24, 131 0. 06 Alpha Max Alpha Energy Particle size handled 5. 50 Me. V < 1 μm 5. 16 Me. V 5 – 10 μm Decay Heat (W/kg) DAC (µCi/m. L) 560 6 E-12 (Type M) 1. 9 6 E-11 (Type S) Half Life (Years) Specific Activity (Ci/g) Mode of Decay u Specific Activity 275 times greater than Pu-239 u Small amounts can cause significant self-heating u DAC 10 times less than Pu-239 (aged weapons grade) FLUOR IDAHO PROPRIETARY INFORMATION 5
Alpha Decay Impacts u Alpha Recoil • Atom recoils in the opposite direction from the path of particle ejection following the radioactive decay 234 U Nucleus of its parent atom 238 Pu Nucleus Alpha Particle FLUOR IDAHO PROPRIETARY INFORMATION 6
Alpha Decay Impacts u Aggregate Recoil • Dispersion of additional atoms in an aggregate as a result of alpha recoil. 234 U + < 10, 000 atoms of Pu. O 1 atom 2 238 Aggregate of Pu Alpha Particle • 1 decay of Pu-238 can mobilize ~10, 000 additional atoms. • Contributes to movement and spread of contamination FLUOR IDAHO PROPRIETARY INFORMATION 7
Alpha Decay Impacts u Fragmentation • Fragmentation of Pu-238 lattice structures occurs as a result of aggregate recoil. Alpha Particle Aggregate of 238 Pu 1 atom 234 U + fragmented aggregates of Pu. O 2 • Reduces median particle size - Ball milled to target of 0. 6 µm Reduced to ~ 10 nm (0. 1 µm AMTD) after 30 + years • Decay over time will result in finer mesh aggregates with increased mobility. FLUOR IDAHO PROPRIETARY INFORMATION 8
Alpha Decay Impacts - Spread of Contamination u Fragmentation, aggregate recoil, and alpha recoil • Responsible for Pu-238’s “lifelike” characteristics, moving throughout space without being acted on by an outside force. u Resuspension of nanoparticles (0. 1 µm AMTD) • Easily resuspended • Create an aerosol that travels with air current • Settling time – days to weeks FLUOR IDAHO PROPRIETARY INFORMATION 9
Alpha Decay Impacts – Particle Size u 10 CFR 835 Appendix A DAC values based on ICRP 66 human respiratory tract model • Assumes default particle size of 5 µm u Dose coefficients calculated using IMBA for 0. 1 µm particle (AMTD) • 40% decrease in DAC Nuclide Particle Size (µm) Absorption Type DAC (µCi/m. L) Pu-238 Pu-239 5 0. 1 5 M M S 6 E-12 2. 5 E-12 6 E-11 FLUOR IDAHO PROPRIETARY INFORMATION 10
Lessons Learned u Disproportionately high number of safety incidents related to Pu-238 (SRS) • > 100 times as more Pu-239 than Pu-238 • 3. 5 times as many incidents related to Pu-238 u Instances of Pu-238 particles found hundreds of feet from containment, rather than settling directly u “lifelike” • Fines appeared to “fly” through the air or “walk” along pipes. • Behave more like a gas than a solid FLUOR IDAHO PROPRIETARY INFORMATION 11
Borescope u Foam • Minimal access and visibility FLUOR IDAHO PROPRIETARY INFORMATION 12
Borescope u Surveys • Contamination mostly contained by the foam or sealed within gloveboxes FLUOR IDAHO PROPRIETARY INFORMATION 13
Control Contamination u Waste Processing Containment FLUOR IDAHO PROPRIETARY INFORMATION 14
Control Contamination u Waste Processing Containment u Ventilation is the primary contamination control u Multiple air movers • 2 point source hoses • 1 over SWB • 1 for attachment to waste box u 80 ft/min at doors u CAMs and FAHs FLUOR IDAHO PROPRIETARY INFORMATION 15
Control Contamination u Waste container as a “hood” FLUOR IDAHO PROPRIETARY INFORMATION 16
Control Contamination FLUOR IDAHO PROPRIETARY INFORMATION 17
Control Contamination u PPE • Tapped Seam Tyvek - Class 2 (PF of 50) • Aprons • Gauntlets/Cut & Puncture u Apply Fixative u Body positioning • Work upstream from items u Minimize handling • Reduce resuspension u Use Reach Tools • Sufficient airflow between worker and contaminated u Air monitoring & Admin. Controls. Du. Pont Tyvek Classic Plus Coveralls FLUOR IDAHO PROPRIETARY INFORMATION 18
Contamination Event u Increasing DAC after moving a section of a large item into a SWB u Complete evacuation of WPC within 15 s of notification (CAM at ~ 1000 DAC) u CAM activity continued to increase over a 5 min period to 36, 000 DAC u Contamination • • u 30 k – 80 k dpm/100 cm 2 alpha on outer Tyvek suits (3 individuals) 2, 778 dpm/100 cm 2 alpha on modesty clothing (1 individual) 1. 9 - 29. 9 DAC-hr, initial count of lapel filter (3 individuals) No skin contamination, nasal swabs < MDA, bioassays < MDA Fixative was not applied after size reduction FLUOR IDAHO PROPRIETARY INFORMATION 19
Phase II u New WPC • Phase 2 waste 0. 030 g – 6. 373 (108. 98 Ci) • Larger boxes • > Pu-238 Content • Size reduction u Advantages • Unidirectional airflow • Up/down stream zones • Space FLUOR IDAHO PROPRIETARY INFORMATION 20
Conclusions u Implementation of a higher degree of engineering controls and PPE than has been applied to previous work with Pu-239/Am-241 • • u Mobility of Pu-238 Specific activity of Pu-238 Small particle size Lessons leaned on contamination control Engineering controls are the primary and preferred method • Administrative controls alone cannot stop the spread of a contaminant that has the ability to move without outside forces being exerted on it. FLUOR IDAHO PROPRIETARY INFORMATION 21
References • • • 10 CFR 835, Occupational Radiation Protection, U. S. Department of Energy; 2007. DOE-HDBK-1145, Radiological Safety Training for Plutonium Facilities; 2013. ICP Technical Baseline 559, Pu-238 Evaluation for Internal Exposure; 2017. Transport of Radioactive Material by Alpha Recoil, A. S. Icenhour, 2005, ORNL/TM-2005/22 INL/EXT-08 -14017, Evaluation of Aqueous and Powder Processing Techniques for Production of Pu-238 Fueled General Purpose Heat Sources, Idaho National Laboratory, U. S. Department of Energy; 2008. SRNL-STI-2009 -00239, Properties and Behavior of 238 Pu Relevant to Decontamination of Building 235 -F, Savannah River Nuclear Solutions, U. S. Department of Energy; 2009. This presentation has been created by Fluor Idaho, LLC under Contract No. DEEM 0004083 with the U. S. Department of Energy. The United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this presentation, or allow others to do so, for United States Government purposes. FLUOR IDAHO PROPRIETARY INFORMATION 22
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