Ra ANALYSES ON SAVANNAH RIVER SITE HIGH ACTIVITY WASTE TANK RESIDUES

Transcription

1 226 Ra ANALYSES ON SAVANNAH RIVER SITE HIGH ACTIVITY WASTE TANK RESIDUES D. DiPrete, C. DiPrete, C. Coleman, M. Hay, S. Reboul, T. Aucott 61st Annual Radiobioassay & Radiochemical Measurements Conference

2 Savannah River Site High Level Waste Flowsheet F-Canyon SRS Production Reactors No longer in service H-Canyon Waste Receipt & Storage Tanks Waste Receipt & Storage Tanks Sludge Processing Sludge Slurry 2H Evaporator System Recycle 3H Evaporator System Interim Processes 2F Evaporator System Feed Staging Tanks ARP DDA MCU Glass Canisters to Yucca Mountain DWPF Spent MST & Cs stream Spent MST from ARP & Cs stream from MCU Keep going for information on SRNL family colors. SWPF (under construction) Decontaminated Salt solution Saltstone Processing Facility 50 Saltstone Vault 2

3 16.9 Mgal 212 MCi 16.6 Mgal F and H Tank Farms Dominant chemical Salt Supernate Saltcake & radiological constituents Sodium nitrate Sodium nitrite Sodium hydroxide Sodium aluminate Cs-137 Crystallized sodium nitrate Cs MCi 3.0 Mgal Sludge Metal (Fe, Mn, Al) oxides & hydroxides Sr-90, actinides Two tank farms 49 waste tanks 22 old-style tanks 27 new-style tanks Approximately 37 million gallons of waste

4 SRS Laboratories Conducting Radiochemical Analyses Savannah River National Laboratory Science and Technology Division Analytical Development Section Analytical Laboratory Department National Security Division Non-Proliferation Technology Ultra Low Level Radioactive Matrices for Forensics/Non- Proliferation F&H Lab (24/7) High Radioactive Matrices H-Canyon/B-Line Process Support SRR Process Support High Activity Forensic Measurements SRNS/ESS&H B Area Lab Environmental Radioactive Matrices Environmental Monitoring Bioassay Nuclear Measurements Group High to Environmental Radioactive Matrices R&D Activities Radiochemistry Support Site Process Support for Activities not Covered by ALD Laboratories High Activity Forensic Measurements Hold-up/NDA in-situ SRS measurements

5 Analytical Development Tasked to Conduct Radiological Characterizations on SRS Waste Tanks Slated for Closure 6 Tanks Characterized thus far Tank 19F in 2009 Tank 18F in 2009 Tank 5F in 2011 Tank 6F in 2011 Tank 16H, primary and annulus in 2013 Tank 12H in 2015 Residues are highly radioactive, and vary from tank to tank (up to 8E10 dpm/g beta, 1E9 dpm/g alpha) Required to analyze for trace radionuclides (as low as to 22 dpm/g in some cases) in the presence of gross levels of interfering radionuclides Large list of analytes (up to 54 radioisotopes), requested for up to ~40 samples of Tank Waste Short turnaround time (development to completion) for the entire effort (~5 months)

6 Nuclear Measurement Group s Radiochemistry Capabilities Beta Spectrometry - Triple, double, single PMT LSC counters, Compton Suppressed LSC, Portable Beta Spectrometers, Conversion electron spectrometer, GFPCs, Beta PIPS Neutron Activation Analysis & Tracer Production Alpha Spectrometry ~100 alpha PIPS + some portable alpha spectrometers Radiochemistry Staff (11) 1 PhD Nuclear Chemist, 2 PhD Nuclear Engineers, 1 MS Radiochemist, 1 MS Biochemist, 2 BS Chemists, 2 Laboratory Technicians, 1 Specialist Gamma Spectrometry ~15 shielded spectrometers ranging from planar to coaxial to well HPGe, several automated + additional portable systems Radiochemistry Prep Laboratories 10 Radiohoods, 3 Radiobenches, 3 Gloveboxes, 2 Chemical Hoods Leveraged Resources SRNL Shielded Cells & other ADS Analytical Instrumentation

7 Tank Closure Campaigns Pictures of 2 SRS Waste Tanks Following Mechanical Cleaning Tasked with conducting radiological characterizations on SRS Waste Tanks slated for closure Waste tanks slated for closure have been mechanically or chemically cleaned Residues are highly radioactive, as high as 8E10 dpm/g beta, 1E9 dpm/g alpha Required analyses for trace radionuclides (as low as 22 dpm/g) in the presence of gross levels of interfering radionuclides Large list of analytes requested for numerous samples of Tank Waste (up to 40 in recent campaigns) Cs-137 is the main contributor to whole body dose Sr-90/Y-90 main contributor to extremity dose Radiochemical separations run much more efficiently in radiohoods as opposed to the shielded cells

8 Tank 19F and Tank 18F Characteristics Tanks were cleaned by mechanical grinding Tank 19 was primarily zeolite Cs-137, 1.5E9 dpm/g Sr-90/Y-90, 1E7 dpm/g Total Pu, 2E6 dpm/g Tank 18 was a mixture of zeolite and more typical tank sludge Cs-137, 8E8 dpm/g Sr-90/Y-90, 2E8 dpm/g Total Pu, 2E7 dpm/g Sample aliquots were weighed in the shielded cells, but all separations carried out in radiohoods

9 Tank 5F and Tank 6F Characteristics Tanks were cleaned using an oxalic acid based cleaning technique, chemistry of samples completely different In addition to tank bottoms, tanks have extensive cooling coil network requiring characterization of residuals Tank 5F Sr-90/Y-90, 5E10 dpm/g Cs-137, 9E8 dpm/g Total Pu, 3E7 dpm/g Tank 6F Sr-90/Y-90, 7E10 dpm/g Cs-137, 1.2E9 dpm/g Total Pu, 3E7 dpm/g Tanks 5F and 6F much more radioactive than 18F and 19F

10 Higher Radiological Activities Required Different Approach Initial sample preparation in shielded cells for a number of methods Tc-99 I-129 Am & Cm isotopes Th-229, 230 Pa-231 Cl-36 K-40 Se-79 Ra-226 C-14 Methodologies had to be adjusted for the above, separations added for others (i.e. Nb-94)

11 1 st tank from H Tank Farm Tank 16H Different processes fed H tank farm than F tank farm Tank 16H had been subjected to an aggressive chemical regimen in the 1980 s Tank residuals were essentially either piles of rust from the cooling coils or piles of rust coated with high levels of Sr-90/Y-90 (1.3E10 dpm/g) Hot particle issues Lack of isotopes which are normally quite easy to quantify (i.e. Cs-137) ironically provided a unique challenge Tank 16 primary walls breached, so annulus was full of highly radioactive residues mixed with sand Sr-90, 7E9 dpm/g Cs-137, 1.6E9 dpm/g Plutonium, 9E6 dpm/g (predominantly Pu-238)

12 Tank 12H Brought a new challenge Tank was receipt tank for some of SRS s thorium campaigns Waste ~7 wt% thorium Thorium is tetravalent, which impacts: Actinide extractions Zr-93 extraction Y-90 clean-up steps etc havoc on low level Th-229, Th-230 measurements Tank was high in Hg ~10 wt% Hg Causes waste issues, wasn t sure about effect on various separations Tank residue highly radioactive Sr-90/Y-90, 8E10 dpm/g Pu-239, 1.6E8 dpm/g Cs-137, 1.3E7 dpm/g

13 Ra-226 Natural Decay Series Uranium used at SRS was enriched for reactor fuel, or depleted for targets to generate Pu-239 No uses for natural uranium at SRS, no obvious source term for Ra-226

14 226 Ra Flowsheet for Tank Closure Samples 0.25g sample 0.25g sample, spiked with Th-228/Ra-224 Samples digested via peroxide fusion, followed by matrix adjustment to ~3N nitric acid Dissolutions decontaminated in shielded cells with a 5 minute contact with Bio-Rad AMP, Eichrom Sr, and Eichrom Diphonex resins Solutions decontaminated further in radiobenchs with treatments of Actinide resin, Bio-Rad AMP, and Eichrom Sr Acid Concentrations adjusted to 0.5M nitric acid, additional Bio-Rad AMP strike conducted Ra extracted with 4mL bed of cation resin Resin eluted with 6M nitric acid, through an Eichrom Sr resin cartridge Eluate concentrated, counted using a 70% HPGe Well Gamma Spectrometer after 1, 3 and 14 days

15 Ra-226 Natural Decay Series Primary Gamma Emissions Ra kev (3.64%) Pb kev (18.4%) 391 kev (35.6%) Bi kev (45.5%) Ra-224 no gamma emissions 186 kev (3.64%) Pb kev (43.6%)

16 Gamma Spectrometry Analysis Samples Counted on a 70% Efficient HPGe Well gamma spectrometer mounted inside a Changer Labs automated sample changer 24 hour Post Separation Count 3 Day Post Separation Count (for Pb-212) Used to quantify Ra-224 tracer yield Decay corrected appropriately 14 Day Post Separation Count (for Pb-214) Used to quantify Ra-226 Batch consists of: sample sample traced with Ra-224 Lab blank Cell blank (if applicable) Ra-226/Ra-224 calibration spike Used to correct for known biases Ra-226/Ra-224 quality assurance spike %

17 Sample Ra-226 Gamma Spectra Pb-212 Am-241 Cs-137 Co-60 Ra-226 Pb-214 Bi-214 Pb-212 Co-60 Pb-212 Co-60

18 Ra-226 Results to Date We keep proving the negative Tank 19, Ra-226 <2.82E-5 uci/g Tank 18, Ra-226 <6.42E-5 uci/g Tank 5, Ra-226 <6.81E-4 uci/g Tank 6, Ra-226 <2.65E-3 uci/g Tank 16, Ra-226 <3.15E-4 uci/g Tank 12, Ra-226 <4.68E-4 uci/g Now looking at optimizing the process: use less sample, eliminate shielded cells steps, streamline overall analysis

19 Options to Aid Separation HDEHP (Eichrom Ln Resin) Use of getters (i.e MnO2 or MST) Precipitation steps(baso4)

20 Options - IBC s Superlig 640 (3M Empore Radium Disk) System extracts Ra in 2N nitric acid Elutes in 0.25M EDTA Literature has conflicting information, consensus is: system is selective for Ra with some affinity for Sr, high affinity for Ba high affinity for Pb

21 Evaluation of Empore Ra Disk Evaluated Ra, Sr, Eu and Sn retention of Ra Disks Sr and Eu were tested in 20mL 2N nitric acid load solution Ra-226 were tested in 40mL 2N nitric acid load solution Ra-224 and Sn-126 were tested with 2mL of SRS Waste Tank Supernate, diluted to 40mL with 2N nitric acid Real waste was treated with two strikes of 0.2g Bio-Rad Ammonium Phosphomolybdate to remove Cs-137 Filters conditioned with 50mL 2N nitric acid Filters rinsed with 150mL 2N nitric acid Filters were removed and analyzed by gamma PHA or LSC For Ra, Sn and Eu, samples analyzed with 70% efficient HPGe Well For Sr-90, filters were added to 20mL Ultima Gold AB and analyzed by LSC

22 Evaluation of Empore Ra Disk Ra-226 recoveries in spiked blanks were 84% and 87% Ra-224 recoveries in SRS supernate were 87% and 95% Sr-90 recoveries in spiked blanks were quantitative 102%, 105%, 105%, samples counted ~2hrs after separation Y-90 growing back in, follow-up equilibrium count underway Eu-154 recoveries in spiked blanks were 0.1%, 0.08%, and 0.004% Sn-126 recoveries in SRS supernate were < 0.62%, and <0.61%

23 Options Low Background Compton Suppressed Gamma Spectrometer Currently using automated 70% HPGe well detector Evaluating use of a comptonsuppressed-low-background 30% HPGe well detector

24 Options Alpha Spectrometry for Radium Isotopes Would need sufficient decontamination of actinides and Sr-90 dose issues Sensitivity superior to gamma Would still need gamma measurements last tank closure suite added Ra-228

25 Conclusions Tank closure radiological characterizations continue to generate analytical challenges Tend to come together in a rush, with analysis requirements continually evolving right up to sample submission While each tank analysis can build on experience from previous analyses, the tanks often generate different matrices Different process waste streams in different tanks An analyte that wasn t a challenge to measure in one tank drops to levels in a second tank that become a challenge Analytes increase in some tanks, interfering with tracer levels used in radiochemical procedures on previous tanks Numerous options currently being considered to accelerate various tank closure analyses, including methodology for Ra-226 Empore Ra Disks have promise, but Sr-90 will have to be dealt with separately