New Generation Dresden NPP Demineralizer Vault Cleanup Project
- CHMM, REP, Vice President, Technology Development, Engineering and Technology Div., Energy Solutions, Inc., Oak Ridge, Tennessee (United States)
- Energy Solutions, Inc., Columbia, South Carolina (United States)
- Corporate Radwaste Manager, and Tom Britt, Chemistry/Radwaste Specialist, Exelon Nuclear, Chicago, Illinois (United States)
Electro-coagulation (EC) is a technique that facilitates rapid destabilization and flocculation of colloidal suspensions to cause the suspended solids to separate from slurry phase. It is generally accepted that coagulation is brought about primarily by the reduction of the net surface charge to a point where the colloidal particles, previously stabilized by electrostatic repulsion, can approach closely enough for van der Waals forces to hold them together and allow aggregation. In the EC process, the coagulant is generated in situ by electrolytic oxidation of an appropriate anode material (aluminum in this case). In this process, charged ionic species, metals or otherwise, and suspended solids are removed from wastewater by allowing them to interact with an ion having opposite charge, or with floc of metallic hydroxides generated electrochemically within the effluent. Typically, no supplementary organic polymer coagulant addition is required. Thus, electro-coagulation (EC) was found to be an attractive treatment option to rapidly destabilize the colloidal particulate phase, allowing more facile particulate removal by decantation and/or coarse filtration. However, the liquid medium must have some conductivity (> 100 {mu}mho is preferred), in order to allow effective electrical coupling with the EC electrodes. A very small amount of aluminum or sodium sulfate salts can be added to the feed slurry, adjusting the water quality parameters to a conductivity of >100 {mu}mho and a pH value near 6.0-7.0. The EC-treated vault slurry had a pH value near 6.5 (within the pH range for minimal solubility of amphoteric aluminum hydroxide). In contrast to untreated wastewater, the agglomerated particles in the EC-treated aliquot could be filtered relatively rapidly, yielding a clear filtrate, indicating that the flocs that have been formed are now > 20- {mu}m in size, are pumpable (high shear strength), and filterable/dewaterable with ease (low water content). Final waste volumes also show that the actual volumetric fraction of solids produced are relatively small. In order to estimate the amount of material (Al or Fe depending on the electrode material) added by the EC process, a rough rule of thumb has been found to be {approx}15 ppm per amp-minute. It was found with most wastewaters that Cs seeding (if that step is required) added {approx} 100 ppm Cs Seed and 10-15 ppm/amp minute additional floc from the electrodes. In a typical BWR wastewater case, where the TSS represented {<=} 0.15 wt% ({approx}1500 ppm). At 1.5 amp-min., the Al (III) added by the EC process would be {approx} 20 ppm, or {approx} 60 ppm as Al(OH){sub 3}. It was found the relatively low floc [{approx} 40 ppm as dried Al(OH){sub 3}] worked quite well for the high colloid level present ({approx}1500 ppm), and would be even more enhanced with the use of recycle. Even at that relatively low treatment dose, the colloidal TSS in the wastewater was effectively flocculated to yield agglomerates that were easily filtered and dewatered. Another rule of thumb is that, empirically, TDS (in mg/l) is typically {approx}0.5 X conductivity (in umho/cm). For instance, a conductivity reading of 100 umho/cm corresponds to about 50 ppm of TDS. As can be seen, the amount of material actually added in this vault cleanup of {approx}15 ppm per amp-min compared to the existing {approx}1500 ppm of TDS present (0.5 X conductivity of 3000 {mu}mho/cm) is minimal. In this vault cleanup, as a precautionary measure, the HIC was a specially designed Press-Pak with internal sheet filters, final dewatering leg, and a expandable, outer bladder if needed for final dewatering. It was found after filling the first HIC, of two, that the material dewatered and passed final dewatering tests without the need for the precautionary Press-Pak feature. Original estimates by the evaluation team estimated it would take some 11 to 12 HICs to remove the vault contents to a remote location for treatment, dewatering and final shipment. With the use of the SAFE{sup TM} Solution, the project was completed during the months of June and July and required only 2 HICs at the 85% fill level. These dewatered HICs were then clear for DOT transport and were shipped to the Clive, Utah Energy Solutions Site for final disposal. During the past year, additional refinements to the patented SAFE{sup TM} Solution have included the SAFER{sup TM} System (Scalant and Foulant Electronic Removal) for the removal by EC of silica, calcium and magnesium. This has proven to be an effective enabler for RO, NF and UF as a pretreatment system. Advantages here include smaller, more efficiently designed systems and allowed lower removal efficiencies with the removal of the limiting factor of scalants. The SAFEST{sup TM} System (SAFE Synergistic Technology) further enables RO systems by utilizing the brine RO reject to supply conductivity to the EC process, while, not only removing scalants, but minimizing brine normally going to further processing such as spent condensate resins or thermal treatment. Similarly, the SAFE{sup TM} System has been applied in the form of a BAC-UP{sup TM} System (Boric Acid Clean- Up) as an alternative to more complex RO or boric acid recycle systems. Lastly, wastewaters have been treated from different DOE sites and fuel reprocessing plants for the removal of totally soluble, TDS, species (e.g., Cs, Sr, Tc, Am, Pu, etc.). For these applications, an ion-specific seed (an element of the SMART{sup TM} System) was coupled with the soluble species prior to EC and subsequent filtration and dewatering, for the effective removal of the high-level complex and the segregation of low level and high level waste steams (LLW and HLW). This will become of paramount importance as Class B and C disposal sites are closed in the near future and maximizing Class A waste for disposal and minimizing > Class C waste volumes for storage become the prevailing goals. (authors)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 21326142
- Report Number(s):
- INIS-US-10-WM-08377; TRN: US10V0573067507
- Resource Relation:
- Conference: WM'08: Waste Management Symposium 2008 - HLW, TRU, LLW/ILW, Mixed, Hazardous Wastes and Environmental Management - Phoenix Rising: Moving Forward in Waste Management, Phoenix, AZ (United States), 24-28 Feb 2008; Other Information: Country of input: France
- Country of Publication:
- United States
- Language:
- English
Similar Records
Separation of nitrocellulose fines from wastewater with polymers
Removal of cadmium from aqueous solution using adsorptive bubble separation techniques