New Innovative Electrocoagulation (EC) Treatment Technology for BWR Colloidal Iron Utilizing the Seeding and Filtration Electronically (SAFE™) System
Authors: Denton Mark S. , Bostick William D. 
Published: June 2009

The presence of iron (iron oxide from carbon steel piping) buildup in Boiling Water Reactor (BWR) circuits and wastewaters is decades old. In, perhaps the last decade, the advent of precoatless filters for condensate blow down has compounded this problem due to the lack of a solid substrate (e.g., powdex resin pre-coat) to help drop the iron out of solution. The presence and buildup of this iron in condensate phase separators (CPS) further confounds the problem when the tank is decanted back to the plant. Iron carryover here is unavoidable without further treatment steps. The form of iron in these tanks, which partially settles and is pumped to a de-waterable high integrity container (HIC), is particularly difficult and time consuming to dewater (low shear strength, high water content). The addition upstream from the condensate phase separator (CPS) of chemicals, such as polymers, to carry out the iron, only produces an iron form even more difficult to filter and dewater (even less shear strength, higher water content, and a gel/slime consistency). Typical, untreated colloidal material contains both sub-micron particles up to, let’s say 100 micron. It is believed that the sub-micron particles penetrate filters, or sheet filters, thus plugging the pores for what should have been the successful filtration of the larger micron particles. Like BWR iron wastewaters, fuel pools/storage basins (especially in the decon. phase) often contain colloids which make clarity and the resulting visibility nearly impossible. Likewise, miscellaneous, often high conductivity, wastesteams at various plants contain such colloids, iron, salts (sometimes seawater intrusion and referred to as Salt Water Collection Tanks), dirt/clay, surfactants, waxes, chelants, etc. Such wastestreams are not ideally suited for standard dead-end (cartridges) or cross-flow filtration (UF/RO) followed even by demineralizers. Filter and bed plugging are almost assured. The key to solving these dilemmas is 1) to break the colloid (i.e., break the outer radius repulsive charges of the similar charged colloidal particles), 2) allow these particles to now flocculate (floc), and 3) form a type of floc that is more readily filterable, and, thus, dewaterable. This task has been carried out with the innovative application of electronically seeding the feed stream with the metal of choice, and without the addition of chemicals common to ferri-floccing, or polymer addition. This patent-pending new system and technique is called Seeding And Filtration Electronically, or the SAFE™ System. Once the colloid has been broken and flocking has begun, removal of the resultant floc can be carried out by standard, backwashable (or, in simple cases, dead-end) filters; or simply in dewaterable HICs or liners. Such applications include low level radwaste (LLW) from both PWRs and BWRs, fuel pools, storage basins, salt water collection tanks, etc. For the removal of magnetic materials, such as some BWR irons, an ElectroMagnetic Filter (EMF) was developed to couple with the ElectroCoagulation (EC), (or metal-Floccing) Unit. In the advent that the wastestream primarily contains magnetic materials (e.g., boiler condensates and magnetite, and hemagnetite from BWRs), the material was simply filtered using the EMF. Bench-, pilot- and full-scale systems have been assembled and applied on actual plant waste samples quite successfully. The effects of initial feed pH and conductivity, as well as flocculation retention times was examined prior to applying the production equipment into the field. Since the initial studies (Denton, et al, EPRI, 2006), the ultimate success of field applications is now being demonstrated as the next development phase. For such portable field demonstrations and demand systems, a fully self enclosed (secondary containment) EC system was first developed and assembled in a modified B 25 Box (Floc-In-A-Box) and is being deployed to a number of NPP sites. Finally, a full-scale SAFE™ System has been deployed to Exelon’s Dresden NPP as a vault cleanup demand system. This is a 30 gpm EC system to convert vault solids/sludges to a form capable of being collected and dewatered in a High Integrity Container (HIC). This initial vault work will be on-going for approximately three months, before being moved to additional vaults. During the past year, additional refinements to the patent pending SAFE™ System have included the SAFER™ 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. Similarly, the SAFE™ System has been applied in the form of a BAC-UP™ System (Boric Acid Clean-Up) as an alternative to more complex RO or boric acid recycle systems. Lastly, samples were received from two different DOE sites for the removal of totally soluable, TDS, species (e.g., cesium, Cs, Sr, Tc, etc.). For these applications, an ion-specific seed (an element of the SMART™ System) was coupled with the Cs prior to EC and subsequent filtration and dewatering, for the effective removal of the cesium complex and the segregation of low level and high waste (LLW & HLW) streams.