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Management of Commercially Generated Radioactive Waste - U.S. ...

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4.41<br />

side by 29 cm deep. Strict quality assurance by the manufacturer and installer ensures that<br />

every filter will be at least 99.7% efficient for removing particles <strong>of</strong> 0.3 um diameter. A<br />

99.9% efficiency for removing radioactive particles (a decontamination factor (DF) <strong>of</strong> 103)<br />

is taken as a reasonable estimate for each stage <strong>of</strong> HEPA filtration. Higher removals are<br />

achieved by the use <strong>of</strong> multiple stages.<br />

Prefilters are used to remove particles larger than 6 im and have less efficiency for<br />

smaller particles. Prefilters are intended to remove the usual ambient dust from the air<br />

stream and thus double or triple the service life <strong>of</strong> the highly efficient HEPA filter. For<br />

radionuclide release calculations, a 91% efficiency for prefilters in removing radioactive<br />

particles (a DF <strong>of</strong> 10) is taken as a reasonable estimate.<br />

Most nuclear facility designs include final filtration <strong>of</strong> essentially all <strong>of</strong> the air<br />

leaving the facility as well as prior filtration <strong>of</strong> the air leaving individual portions <strong>of</strong><br />

the facility (e.g., some process equipment, cells, glove boxes). This is outlined in the<br />

flow diagram shown in Figure 4.3.12. The final filtration system has been termed the atmos-<br />

pheric protection system (APS). Three types <strong>of</strong> atmospheric protection systems are examined<br />

in detail in DOE/ET-0028 (Section 4.11) for application at fuel reprocessing plants (simi-<br />

lar systems could be used at MOX-FFP and spent fuel treatment facilities). These three APS<br />

types use HEPA filters for final filtration but use different types <strong>of</strong> prefilters. One<br />

type <strong>of</strong> APS employs a commercially available Group III throw-away prefilter, another type<br />

employs a sand-bed prefilter, and the third type employs a deep-bed glass fiber filter.<br />

The Group III prefilter option was chosen as the example case in this Statement.<br />

AIR FROM PROCESS AIR FROM PROCESS AIR FROM CONTAMINATION-<br />

CELLS, GLOVE BOXES, ETC. EQUIPMENT FREE ZONES<br />

PREFILTER PREFILTER<br />

HEPA FILTER HEPAFILTER<br />

HEPA FILTER HEPA FILTER<br />

PREFILTER<br />

HEPAFILTER<br />

DISCHARGE TO ENVIRONMENT<br />

(VIA STACK)<br />

FIGURE 4.3.12. Flow Diagram for Filtration <strong>of</strong> Airborne <strong>Waste</strong>s

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