Reformulation of the LOMI chemical decontamination reagent: Reduction in the picolinic acid/vanadous formate ratio

Most LOMI decontaminations performed in the US have employed ratios of picolinic acid to vanadium in the range 4.5:1 to 6:1. Ratios in this range ensure complete chelation of all metals as the 3:1, or tris, picolinate complexes. Recent studies have suggested that the mono and bis complexes are equally soluble and that it may be possible to reduce the proportion of picolinic acid with a corresponding reduction in the amount of ion exchange resin required. However, before such a reduction can be implemented, it must be shown that it will not result in the precipitation of uncomplexed metallic species such as vanadium hydroxide or iron hydroxide. A methodology has been developed for determining the concentration of all vanadium, iron and picolinate species that exist during a LOMI decontamination. Using published or estimated dissociation constants for each species, concentrations were calculated at the beginning and end of a typical LOMI application. Various values for pH, vanadium concentration, iron concentration and picolinic concentrated were evaluated. These calculations showed that the dominant species at the beginning of a decontamination is vanadium (II) tris picolinate if the picolinic to vanadium ratio is 2.5:1 or greater. At ratios between 1.5:1 and 2.5:1 the bis complex predominates. Based on these results, it is recommended that during LOMI decontaminations the ratio of picolinic acid to vanadium be reduced to 3:1 from the current range of 4.5:1 to 6:1. Such a decrease would result in a reduction of 50% in the amount of picolinic acid required and a reduction of 50% in the amount of anion resin required to remove it. These reductions translate to savings of $200,000 for a single step LOMI BWR full system decontamination and $250,000 for a four step AP-LOMI PWR full system decontamination. The savings associated with sub-system decontaminations are about 1/10 these amounts. 9 refs., 7 figs., 7 tabs