Capture of Uranium Particles By Filtration: Effects of Filter Material and Air Humidity
Filtration of airborne particles is a standard technique for removal of radiological particles from the effluent of a nuclear reactor. The effects of humidity on filter performance and uranium particles are however less understood. We have conducted experimental runs in the Environmental Experimental Chamber (EEC) located at ORNL to study the capture of uranyl fluoride particles in supports of NNSA missions. Two filter types, one of Minimum Efficiency Reporting Value (MERV)-9 and the other of MERV-10 American Society of Heating, Refrigerating and Air-Conditioning Engineering) ASHRAE rating, were used in the investigations under two humidity conditions [15% and 65% Relative Humidity (Rh)]. Both MERV9 and MERV10 filters failed to capture uranyl fluoride particles that were smaller than 100 nm. The penetration efficiencies for both filter types were very high, greater than 80%, for particles from 10 to 100 nm. As particles became larger and wetter, the capturing efficiencies of both types of filter improved. Slightly greater than 50% of particles from 1 to 10 μm still escaped the capture by the MERV9 filters. However, MERV10 filters were able to capture higher than 50% of particles in the size range of 1 to 2 μm indicating it is likely to meet ASHRAE requirements. Overall, the capture efficiency of a filter is highly dependent on uranyl fluoride particle size, which humidity plays a major role. These two filter types simply are unable to capture particles smaller than 1 μm. A filter that has a higher ASHRAE rating like the HEPA filter has to be used to capture sub-micron particles. Questions on how uranyl fluoride behave in a condition higher than 65% Rh remain, because the particles could deliquescent at the higher humidity condition. That would complete change the size, shape, and surface properties of the uranyl fluoride particles which could lead to completely different filter performance and filtration dynamics. Furthermore, how high humidity affects filters of all MERV ratings remain unclear. Other filter characteristics such as surface charge could also be affected by high humidity condition and need to be investigated.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1606911
- Report Number(s):
- ORNL/TM-2019/1337; TRN: US2103954
- Country of Publication:
- United States
- Language:
- English
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