Centrifuge decontaminating

As part of the evaluation, a cost estimate of the centrifugal shot blast technology was prepared based on the demonstrated decontamination of 800 ft of concrete. The vendor provided personnel and equipment for which timed and measured activities were recorded to determine achievable production rates. These data included activity duration, work crew composition,... 

Figure 4. Measured 95Zr decontamination factors (A) estimated DBP level in processing 180-day cooled reference fertile particles in pulsed column (B) same as above with Robatel centrifugal contactor.

Ethyl alcohol and isopropyl alcohol have similar disinfectant properties. They are active against enveloped viruses but their action against nonenveloped viruses is variable. They are used at concentrations of about 70% in water it is necessary to have a wetting agent to assist penetration of the alcohols. Such alcohol solutions may be used to disinfect surfaces and to decontaminate centrifuge buckets. 

Each of these areas must have its dedicated equipment (pipets, tube racks, ice buckets, centrifuges, vortex, freezers, refrigerators, and so on). A good way to prevent transfer of equipment from one area to another is the use of a color code (e.g., green for pre-PCR, white for the isolation area, and so on). A oneway flow is to be respected pre-PCR area —> isolation area (—> nested-PCR area) —> post-PCR area. PCR tubes racks that must go from the pre-PCR area to the nested-PCR area and that eventually come back to the pre-PCR area need to be decontaminated by UV irradiation (20 min on each side) and/or with 10% bleach (overnight incubation). 

The other detrimental effect of TBP degradation is its complexing of zirconium. This increases the zirconium distribution coefficient and consequently decreases the decontamination coefficient. Moreover, solvent residual radioactivity is increased because of incomplete zirconium reextraction. Another and even more troublesome consequence of zirconium complexing is the formation of precipitates known as crud. This is a severe problem, particularly in mixer-settlers, and has led to a preference for pulsed columns or centrifugal contactors in the first extraction cycle when high-burnup fuel is to be processed. 

To keep organic exposure below 0.1 (Wh)/liter, the organic residence time should be below 0.1/1.17 h, or 5 min. Thus, short-residence-time contactors, like the centrifugal contactor specified for Barnwell, are desirable for this primary decontamination service. 

CodecontaminatioiL The codecontamination section consists of the HA extraction section equipped with short-contact-time centrifugal contactors and the HS scrubbing section equipped with pulse columns. In the HA section, uranium and plutonium in the aqueous feed and reflux from the HS section are extracted into the organic stream containing 30 v/o TBP. In the HS section any ruthenium extracted by TBP is scrubbed into the aqueous phase with 3 M HNO3. Then any zirconium-niobium in the TBP is scrubbed with 0.3 M HNOa. Scrubbing is at 50°C to enhance decontamination of ruthenium. 

Flocculation of added FeCh solution by proper addition of Ca(OH)2 removes the bulk of the radionuclides from the spent decontamination solution decontamination factors of up to 500 can be achieved by an appropriate performance. While the resulting volume of precipitate is comparatively high, it can be reduced by separation using a centrifuge-decanter system (Gregoire et al., 1989). Several attempts have been made to process spent decontamination solutions by inverse osmosis, but so far these attempts have been unsuccessful, mainly due to rapid plugging of the membranes. 

Hui et al. [160] utilized specific protocols to compare the effects of different decontaminants. They mixed radiolabeled chemical contaminants with powdered SC and incubated the samples in a 37° C water bath for 0.5-2 h. The chemical and SC mixture was washed several times with selected decontaminant solutions and then centrifuged to separate the washing solution from the SC pellet. Then the radioactivity of each sample was measured [160]. 

Disassembly and decontamination. When the run is over, the rotor, chamber, and all dissociated tubing that was in contact with the agent must be decontaminated. Do not neglect the underside of the chamber lid. If the centrifuge is equipped with a vacuum system, any aerosol of agent may have contaminated the vacuum oil, pump, or piping. The chamber drain in those instruments that have one may also require decontamination. 

In addition to the hazards of heat and glass in the use of the autoclave, a special hazard deserves mention. Cellulose nitrate media such as centrifuge tubes or nitrocellulose filters can be highly reactive and can decompose explosively under the conditions of high heat and pressure present in autoclaves (82, 113). Therefore, never use the autoclave to decontaminate infectious materials present in these media instead, utilize chemical decontamination techniques. Soaking in a 10 percent aqueous chlorine bleach solution for 30 minutes has been recommended (82). 

Examples of some devices which meet only the first criterion are the safety blender (Figure 10.1), centrifuge safety tubes (Figure 10.2), and flexible film containers (Figure 10.3). These devices do limit the amount of material used and contained, but they do not allow easy transfer or decontamination. Therefore, they are not true primary barriers however, they do provide the best possible containment available for mixing and centrifuging operations. The most familiar primary barrier device that meets all three criteria is the biolog-... 

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