Source term reduction initiatives with the fastest return on investment (ROI) have proven to be those which implement enhanced filtration techniques.
Conventional mechanisms of filtration rely on the mechanical structure of the filter media to capture and retain contaminants. With filtration requirements in the reactor coolant system (RCS) at 0.1 microns (μm) simply adding more and finer material does not insure higher removal rates. In fact in many instances it has been shown to be counterproductive as the pressure losses due to the lack of permeability result in more frequent filter change-outs and higher costs not to mention increased risk of exposure from increased frequency of handling.
Even at sub-micron removal ratings, conventional filters rely on the physical structure of the filter media for capture and retention of contaminants. The principal mechanisms of conventional filtration include, direct interception, inertial impaction, filter cake and bridging.
Operators of PHWR reactors identified four (4) distinct areas of research that the development of nano-fiber filter media for nuclear application had to address in order to be considered for use in their systems.