High-activity waste stream

Activated carbon has been tested for the cleanup of highly colored waste streams such as result from dyeing operations [78]. Coal carbons are 99% effective for dye removal and accept dye loadings as high as 0.40 kg dye/kg carbon. Lignite carbon is also useful, but less effective. 

The high-level waste stream may consist of from 10s-106 gallons per year of an aqueous solution of various inert salts, ranging from 0 to 20 % of total solids contaminated with 10 to 100 parts per million of fission products. The activity level of such a waste would be in the hundreds of curies per gallon range, so that even small samples of such waste would be dangerously radioactive. 

During the decontamination steps, acid streams containing small amounts of actinides and fission products are produced. These streams are evaporated to concentrate the metal ions and recycle them. Nitric acid is recovered from the condensates and recycled. Excess HNO3 may be destroyed by formaldehyde. Fission product concentrates are routed to the aqueous raffinate of the first extractor of the partitioning cycle which contains > 99% of the FP. This constitutes the high level liquid waste (HLLW, or alternatively called HAW, high active waste). All other liquid wastes can be subdivided into intermediate level waste... 

The highly tritiated waste streams discussed here represent a legacy waste from the operation of the Chapelcross Process Plant (CXPP) production line. This facility was operated until 2006 to produce purified tritium for the Military of Defence weapons programme. The primary (although not only) source of contamination in the waste is machine lubricating oil from rotary vacuum pumps used in the process line to evacuate air from the tritium purification process. The innovative design of the plant however led to substantial oil tritiation. The current activity of which is governed by two factors the extent of tritiation whilst in use (i.e. duration of service) and subsequent decay time since termination of service. 

Despite these limitations both methods represent the best techniques currently available and a marked improvement in the knowledge of the tritium inventory of this highly tritiated waste stream when compared to historical Chapelcross paper records which are now superseded. Previous work to determine the specific activity utilised the application of a highly conservative activity conversion factor from liberated gaseous tritium in equilibrium with a solid matrix inside a sealed container to an in-situ P measmement of gaseous tritium. Consequently the maximum specific activity has been determined to be < 25 % of the previous assessment and provides sufficient surety of true activity to support the appropriate onward waste management routing decision for this unique waste stream. 

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

The highly selective biocatalytic reactions afford a substantial reduction in waste. The overall isolated yield is greater than 90%, and the product is more than 98% chemically pure with an enantiomeric excess of >99.9%. All three evolved enzymes are highly active and are used at such low loadings that counter-current extraction can be used to minimize solvent volumes. Moreover, the butyl acetate solvent is recycled with an efficiency of 85%.The E factor (kgs waste per kg product) for the overall process is 5.8 if process water is excluded (2.3 for the reduction and 3.5 for the cyanation) [47]. If process water is included, the E factor for the whole process is 18 (6.6 for the reduction and 11.4 for the cyanation). The main contributors to the E factor are solvent losses which accounted for 51% of the waste, sodium gluconate (25%), NaCl and Na2SO4 (combined circa. 22%). The three enzymes and the NADP cofactor account for <1% of the waste. The main waste streams are aqueous and directly biodegradable. 

Adsorption by activated carbon is commonly employed for the removal of TNT from aq waste streams, eg, pink water formed in shell-loading operations. Low efficiency in regeneration of the carbon for reuse has led to a study of the factors involved (Ref 99), with conclusions as follows. The TNT is adsorbed at many of the numerous high-energy sites on the surface of the carbon. Basic materials, introduced during activation of the carbon by combustion and oxidation and also present at these sites, then induce oxidation-reduction reactions of the methyl with the nitro groups in the TNT. This is... 

While cleaning up previous contamination is a high priority, developing new technologies to prevent future contamination is equally important, if not more so. Without environmentally acceptable industrial processes, power production, and consumer activity, the Earth s environment will continue to be threatened. Development of inherently clean technologies as well as implementation of effective waste stream treatment are viable routes to preventing future environmental contamination. 

Finding 3-4. Contaminated activated carbon from the treatment of several different waste streams is a major waste disposal problem at all chemical agent disposal facility sites. The micronization pretreatment of activated carbon in preparing it to be destroyed by on-site incineration has been shown to be a highly problematic process option. 

The PVC industry is actively involved in the development of recycling solutions for contaminated mixed plastics waste streams with a high PVC content. Potential technologies for achieving this goal are tested at present at pilot scale. This paper provides an overview of the projects under investigation and the results obtained so far, while development work continues. 9 refs. 

The fission products (Cs, Sr, Ba, and Tc) are found in waste streams with significantly high activity and comparatively short half-life (see Table 17.2). Their initial high activity requires that these elements must be stabilized in a waste form that is not affected by selfradiation. 

We, at the Verandsky Instimte of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, have recognized this and have already initiated research on these materials for stabilization of some difficult high activity radioactive waste streams. The simple concept of forming these ceramics by acid-base reaction, the resulting room-temperature fabrication processes, and the superior properties of the product ceramics, all presented in this book, are helping us to solve some difficult... 

Technetium-99 Tc-99 is a reasonably high-yield (6%) FP (similar to Cs-137). The ratio of activities Cs-137 to Tc-99 is calculated (FISPIN) to be 6,000 to 1. Of the selected waste streams in the UK Nirex Inventory, 18 were found to exceed the GQ level for Tc-99 including HPA SPF (high uncertainty), FED and miscellaneous contaminated items (MCI), and HNA FCC, MCI and IX resin. Tc is chemically different to Cs because it will form anionic species (the pertechnetate anion, TCO4 ) whereas Cs will only form cations. Tc-99 will not be retained by the standard resins used to remove Cs. Cs-137 will therefore not be a good marker for Tc-... 

A further review of the underpinning research and development activities of high priority projects will establish whether the level of activities (basic science and contingency work) are aligned to the uncertainties and risks associated with the projects. Whilst NDA believe these high priority projects are technically underpinned against current plans, the level of risk associated with the waste streams involved may require more investment to develop contingency options in parallel. 

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