Speaker
Description
Foam decontamination process has a potentially wide application in the removal of contaminants from large components with complex shapes or large area or large volumes. This process can be applied to any direction regardless of walls, floors and ceilings, and basically it has the advantage of generating less secondary wastes. However, there is a disadvantage that the decontamination factor (DF) is relatively low only by one batch application. In order to improve the DF of the foam decontamination process, many attempts have been made to introduce various chemical decontamination agents into the foam and enhance the contact time of the foam between the chemical decontamination agent and the contaminated surface by introducing a viscosifier to improve the stability of the foam. In this study, we investigated the effects of 'push-blowing' cyclic foam filling process in which newly generated foam is periodically brought into contact with the surface of the decontamination object, rather than the 'one batch application' process which applies the decontamination foam only once. In addition, the decontamination performance of the foams containing various chemical components such as chemical reagents and silica nanoparticles was evaluated according to the characteristics of surface contamination of the decontamination object. Decontamination performance tests were carried out by applying various decontamination foams to the simulated specimens contaminated with non-fixed particles and oil, and the specimens with fixed corrosion oxide films. The decontamination performance was improved by keeping the physicochemical properties of the decontamination foam substantially constant by applying 'push-blowing' cyclic foam filling process. In the removal of contaminants from the simulated specimens by the decontamination foam, non-fixed contamination consisting of a mixture of Eu2O3 particles, TBP and fluorescent material was completely removed within 4 hours by neutral decontamination foam containing 1 wt% of M-5 silica nanoparticles and 1 wt% of EM100 nonionic surfactant. For the removal of the fixed contaminants, the NiFe2O4 film coated on the stainless steel specimen having a thickness of 500 nm was completely removed within 2 hours by decontamination foam composed of 0.5M HF, 0.5M HNO3 and 1 wt% EM100. On the other hand, only about 3% of the NiFe2O4 was removed during the same time period by the decontamination foam consisting of 2 M HNO3, 1 wt% EM100 and 1 wt% M-5. FeCr2O4 film with a thickness of 10 ㎛ produced in the autoclave was completely removed within 2 hours by the oxidizing decontamination foam containing 0.1 to 0.5 M Ce(IV), 2 M HNO3, 1 wt% TBS as an anionic surfactant and 1 wt% M-5 nanoparticles, but almost not by the decontamination foam consisting of 0.5 M HF, 0.5 M HNO3 and 1 wt% EM100. It was found that the corrosion oxide film containing chromium can be removed by the oxidizing decontamination foam while it was difficult to remove by the reducing decontamination foam.
