Down-select ion specific media (ISM) utilization in upset and outage conditions

This paper presents a process that has been used to help nuclear power plant (NPP) clients resolve some of their more challenging waste water processing issues. These treatment issues may become even more evident during outage conditions, due (in part) to associated decontamination activities that may cause off-normal chemical conditions, which may subsequently change both the peak levels of activities for radionuclides introduced into the collected waste water and also the chemical forms in which they may exist (e.g., formation of colloids or soluble chelates). In one NPP waste processing example, a large proportion of soluble Co-58, which is normally present as a soluble cationic species or an uncharged colloidal solid, was found to behave like an anion; formation of an anionic chelation complex was implicated, possibly due to suspect EDTA, or similar additive, in a proprietary decontamination soap formulation. Antimony 125 (Sb125), normally present as a weakly anionic (Sb(OH)6-) or even neutral (Sb(OH)30) species, was being displaced from previously-loaded media by other, more strongly bound species, causing an unacceptable peak activity in water intended for discharge. A quick resolution of the existing waste processing limitations was required, due to limited waste water holding capacity. Samples of the authentic NPP waste water containing the recalcitrant radionuclides were sent to our licensed off-site laboratory (MCLinc), where small-scale batch-equilibrium testing was used to down-select, from a large number (36) of candidate media (both commercially available and developed internally), those that were relatively effective and economical for use in achieving the required discharge criteria. Batch equilibrium testing is very efficient for use in screening the relative effectiveness of contaminant removal by candidate media in a select waste water composition, and can also provide an estimate of the ultimate contaminant loading capacities on the candidate media; however, equilibrium testing does not provide information on the exchange kinetics and the shape of the packed column breakthrough isotherm. The performance of the most promising of the pre-screened media was then further tested and validated at the NPP site, using small packed bed columns containing the media to be evaluated, with use of actual NPP waste water under dynamic flow conditions. In the cited example, dynamic flow testing validated the performance characteristics for the most promising media, as previously-selected by the laboratory batch testing. In particular, it revealed that two novel media were particularly useful under process upset conditions, viz., AGC-5860 (a chemically modified activated carbon) for chelated transition metals (especially Co58 and 60), and ASM125 (a highly selective and tenacious resin product) especially for Sb125. Subsequently, two of the most effective novel media identified in the screening effort have now been deployed at full-scale at an NPP site for the duration of approximately one year (to-date). The antimony-selective resin has performed especially well, greatly outperforming and outlasting previously utilized media, under many variations in the NPP influent waste water composition (including outage conditions and high boron concentrations, etc.). It was further found that the ASM 125 ISM had an excellent affinity for tellurium (Te125m), a daughter of antimony (Sb). (See data from Exelon's Byron Station. Also, on-going at Calvert Cliffs). At the request of two other NPPs (STP and Calvert Cliffs), the AGC ISM was found to solve their Fe 55 and Ni 63 problem, likely resulting from steam generator change outs at the plants. Lastly, work is on-going remove radioactive iodine (I129) with the granulated AGC. (authors)