Spent anion exchange resins: Simulated conditions from CANDU moderator to storage with Ralstonia pickettii

Anion exchange resins are used in the purification system of nuclear reactors to remove contaminants such as C-14, an impurity produced by activation of contaminates in water. After service, the ion exchange resins are spent, and are then discarded as waste in holding tanks. The accumulated spent anion exchange resins currently hold 29% of all man-made C-14, produced in the nuclear era, which currently sits in Canada, and it can be released in the environment. Bacteria are present in at least one of these holding tanks, and the impacts that bacteria may have on anion exchange resins must be further evaluated. In this work, we investigated bacterial survival in conditions similar to holding tanks, and properties of anion exchange resins exposed to simulated reactor conditions, which contributes to the retention or environmental release of C-14. Ralstonia pickettii, a bacterium capable of survival in a nutrient-depleted environment, is currently being explored for survival in simulated, simplified, spent ion exchange resin waste to determine the potential to mobilize exchanged anions, by using the anionic resin backbone as a nutrient source and/or displaced by metabolic byproducts.;We have developed a procedure to gently damage anion exchange resins to a set point, which simulates post reactor conditions. At this set point, 6 trials resulted in an instant degradation rate of 1.3-14 μg C/min·mL. The total amount of carbon released ranged from 5.5 to 22% of the initial carbon in the anion exchange resin. The moisture content increased by 4 to 17%, while the selectivity, total and strong-base capacity decreased by 24 to 63%, 5 to 40% and 18 to 38%, respectively. These results confirm that anion exchange resins can be damaged with measurable properties.;The next step was to inoculate Ralstonia pickettii to ion exchange resins, simulating storage conditions. The effect R. pickettii had on ion exchange resins have been assessed using moisture content, total capacity, strong base capacity and selectivity of nitrate over bicarbonate. R. pickettii was viable for the duration of the 6 month storage period.;R. pickettii did not affect the crosslinking agent on undamaged anion exchange resins and damaged anion exchange resins. The moisture content for anion exchange resins did decrease for all storage conditions, by 0.8 to 6%. Biofouling of the resin pores may have occurred.;Nuclear grade anion exchange resins were oxidatively damaged under controlled conditions (Fe2+/Cu2+/H2O2) in accelerated moderator simulated conditions. Damage to the anionic resins were assessed using changes in resin properties such as moisture content, selectivity, total capacity, strong base capacity, and total organic carbon (TOC) release. Ralstonia pickettii was added to undamaged and damaged anion exchange resins, with and without undamaged cation exchange resins, simulating storage conditions for a period of 6 months. The amount of Cl- released from the anion exchange resins was used as an indicator of resin damage, in addition to the resin property tests.;R. pickettii in contact with undamaged anion exchange resins resulted in a total capacity change of -4 to +7%. The addition of undamaged cation exchange resin resulted in no change to the functional groups of the undamaged anion exchange resins. R. pickettii in contact with damaged anion exchange resins, solely or in a mixed bed, did not significantly affect the functional group.;The selectivity for all R. pickettii contacted anion exchange resins insignificantly decreased by 16 to 49%.;R. pickettii in contact with undamaged anion exchange resins and undamaged anion plus cation exchange resins, resulted in a Cl - decreases of approximately 200 mg/L, each. R. pickettii in contact with damaged anion exchange resins and damaged anion plus undamaged cation exchange resins, resulted in Cl- decreases of approximately 250 and 220 mg/L, respectively.;The carbon-14 release into the environment is believed to be minimal for two reasons: the reduced moisture content when in contact with R. pickettii implies biofouling of the resin pores occurred. Biofouling was also supported by the decrease in Cl- content found in solution after short term storage. The second reason is the reduced selectivity of nitrate over bicarbonate; the reduced selectivity favors C-14 being more strongly held by the anion exchange resin.;The early stages presented in this study suggest that R. pickettii in contact with anion exchange resin while in storage, would be non-detrimental and possibly prevent the mobilization of C-14, mainly through biofouling.