Radioactive Waste Tanks Research Articles

32-Week Holding-Time Study of SUMMA Polished Canisters and Triple Sorbent Traps Used To Sample Organic Constituents in Radioactive Waste Tank Vapor Headspace

Two sampling methods [SUMMA polished canisters and triple sorbent traps (TSTs)] were compared for long-term storage of trace organic vapor samples collected from the headspaces of high-level radioactive waste tanks at the U.S. Department of Energy's Hanford Site in Washington State. The two methods were found to provide generally equivalent results. Because safety, quality assurance, radiological controls, and somewhat complex sample custody arrangements frequently precluded rapid analysis, the long-term stability of the sampling media during storage needed to be addressed. Samples were analyzed with a gas chromatograph/mass spectrometer (GC/MS) using cryogenic preconcentration or thermal desorption sample introduction techniques. SUMMA canister samples were also analyzed for total non-methane organic compounds (TNMOC) by GC/flame ionization detector (FID) using EPA Compendium Method TO-12 . The 31 target organic analytes studied represented compounds with widely varying polarities and volatilities. To verify the long-term stability of the sampling media, multiple samples were collected in parallel from a typical passively ventilated radioactive waste tank known to contain moderately high concentrations of both polar and nonpolar organic compounds. Two sets of sorbent trap samples were collected to compare the effects of storage under refrigerated (−20 °C) and room temperature conditions. Analyses for organic analytes and TNMOC were conducted at increasing intervals over a 32-week period to determine whether any systematic degradation of sample integrity occurred. Analytes collected in the SUMMA polished canisters generally showed good stability over the full 32 weeks with recoveries at the 80% level or better for all compounds studied. The TST data showed some loss (50−80% recovery) for a few high-volatility compounds even in the refrigerated samples; losses for unrefrigerated samples were far more pronounced with recoveries as low as 20% observed in a few cases. Long-term stability for the other compounds studied was deemed to be generally satisfactory at the 80% recovery level.

Rheology of Colloidal Suspensions and its Implication for Tank Waste Processing

The rheology of colloidal suspensions can vary enormously depending on the contents of the suspensions and the details of how they were produced. Certain interactions between particles within colloidal suspensions can greatly affect their rheology which can be a serious impediment to their processing. For example, at DOE's Hanford site, the radioactive tank wastes are very concentrated and have formed a sludge that is too viscous to process. We are interested in understanding the rheology of this system in order to develop an efficient method for processing the waste. Towards this end we have developed a model silica system for the tank wastes whose particles can interact through chemical bonding, Keesom interactions, and Coulombic interactions. Through systematic variation of the solvent and the particle concentration we can alter the rheological behavior from shear thickening to shear thinning to Newtonian. We present preliminary results for this system as it applies to the processing of the tank waste at Hanford.

Caustic recycle from high-salt nuclear wastes using a ceramic-membrane salt-splitting process

Abstract An electrochemical salt-splitting process, based on sodium-ion selective ceramic membranes, is being developed to recover and recycle sodium hydroxide from high-salt radioactive tank wastes in the U.S. Department of Energy complex. The ceramic membranes are from a family of materials known as sodium (Na), super-ionic conductors (NaSICON). Two membrane compositions based on the rare-earth elements, neodymium and dysprosium, and a new proprietary material, NAS-D, have been fabricated as disks and are currently being tested with waste simulants. The membranes have been incorporated into a polyethylene scaffold for implementation into commercially available plate-and-frame electrochemical cells. A purified caustic product with a sodium hydroxide in excess of 3 M was produced from waste simulants with the Dy- and Nd-NaSICON membranes. This is the nominal concentration for onsite recycle and higher concentrations are expected. Membrane fouling was not observed, even though gibbsite {A1(OH) 3 } was precipitated in large amounts during some of the runs. Preliminary testing of the NAS-D material indicates that a sodium current density of 38 mA/cm 2 with a sodium current efficiency of approximately 90% is achievable over 1000 h of operation with an applied potential of 4.5 V.

Thermocouple placement and hot spots in radioactive waste tanks

Abstract Analytical solutions to the differential equation describing the conduction of heat from an instantaneous point source were used to analyze the detectability of hot spots in radioactive waste tanks and the potential for thermally initiating runaway chemical reactions. Graphs are presented based upon diffusivities, times, temperatures and heat generation rates which are representative of conditions in the high‐level liquid waste storage tanks at Hanford. These calculations suggest that achievable temperatures in these tanks are not sufficiently high to initiate runaway reactions. They also suggest that placing thermocouples sufficiently close together to be of use either in locating hot spots, or in alerting the operators in time to have their actions influence subsequent developments, is not practical.

Organic analysis of the headspace of hanford waste tank 241-C-103

Organic species from the headspace of one Hanford radioactive waste tank are described. Samples were collected either using a sorbent trap or a SUMMATM canister and were analyzed by gas chromatograph and mass spectrometry. The headspace contained several organic components, including alkanes, alkenes, ketones, aldehydes, organic nitriles, and chlorinated hydrocarbons. Sorbent trap samples were designed to collect only normal paraffin hydrocarbons (NPHs). A comparison of NPH data from sorbent traps and SUMMATM cans revealed results of 693 and 1320 mg/m3, NPH respectively. Significant differences were observed in NPH values when samples were collected at different times, or at different locations in the tank. These data suggest either the time of collection, or the position of the sampling device are important variables in the analysis of organic species from Hanford tanks.

An HMS/RRAC Analysis of A High-Level Radioactive Waste Tank Farm

It has been observed that a high-level radioactive waste tank generated quantities of hydrogen and nitrous oxide mixture that are potentially well within flammability limits. These gases are produced from chemical and nuclear decay reaction in a slurry of radioactive waste materials. The slurry is covered by a thick crust and containing sodium nitrate and nitrite salts. Significant amounts of combustible and reactant gases accumulate under the crust over a 110- to 120-day period. These gases cause the crust to rupture, allowing the gases to vent into the air cover-gas space above the crust. We postulated an ignition source for the hydrogen/nitrousoxide/air mixture after it has vented into the cover gas, and we calculated the resulting pressure and temperature loading on the double-walled waste tank using the three-dimensional, time-dependent fluid dynamics coupled with the chemical kinetic computer code HMS (Hydrogen Mixing Studies).The waste tank farm has a ventilation system designed to maintain a slight negative gage pressure during normal operation. We modeled the ventilation system with TRAC (Transient Reactor Analysis Code), and we coupled these two best-estimate accident analysis tools to model the ventilation system response to pressures and temperatures generated by the hydrogen combustion. Significant pressure are produced by this event, which could possibly threaten the tank's integrity.

Potential Hazard of Ferrocyanide Salts in High-Level Waste Tanks Within the Hanford Tank Farm

ABSTRACTOver the past few years, there has been an increased awareness of the potential hazard of energetic chemical reactions in high-level radioactive waste tanks at the Hanford tank farm. In particular, a mixture of Na2NiFe(CN)6 with NaNO3 and NaNO2 in several high-level waste tanks has caused concern. The problem of the FeCN tanks is fundamentally one of a potentially unstable mixture of fuel (the CN- moiety) and oxidizer (NO3- or NO2-).At Los Alamos National Laboratory, we have performed an extensive reanalysis of the safety problems associated with the presence of Na2NiFe(CN)6 mixed with NaNO3/NO2 for a particular tank (104-BY) that contains by far the largest amount of the nickel ferrocyanide salt (∼2E5 mol). Our approach is to use conservative assumptions to bound both the energy density for a potential runaway reaction and the mass that could participate if we assume ignition as the result of bounding radionuclide concentrations. The subsequent progress of the accident is analyzed using an advanced hydrodynamics computer code called MESA to evaluate the loads on the structure and the generation of aerosols. The subsequent doses are shown to be low both on and off the site. The conservatism in the analysis is quite large, and the expected results using more realistic assumptions are discussed.

Determination of regulatory organic compounds in radioactive waste samples. Semivolatile organics in aqueous liquids

The regulatory semivolatile organic compounds present in radioactive aqueous waste samples are extracted and concentrated in a small-scale version of a standard EPA procedure normally used for ground waters. Decontamination is sufficient to permit analysis of the extract in a conventional gas chromatography/mass spectrometry laboratory. The performance of the modified procedure, based on surrogate standards, matrix spikes and matrix spike duplicates, and blanks, is comparable to that of the standard method. The modified procedure was applied to a variety of aqueous radioactive waste tank samples. Only 12 of the EPA Appendix VIII compounds were present, and none in concentrations exceeding the reporting limit (500 or 2,500 {mu}g/L). The most common semivolatile present was tributyl phosphate, an organic extractant commonly used in radiochemical processing, at 2,000-30,000 {mu}g/L.