Cleaning capability
The
most quantitative determination of the cleaning capability by ice blast
was by OSEE (Optically Stimulated Electron Emission) spectroscopy. Figure
11 below illustrates the principle of this methodology:
Figure
11: OSEE Spectroscopy
This
detection method is based on the Photoelectric Theory whereby
photoelectrons are released from a metal surface when it is struck by
photons of the proper energy hν. The number of released photoelectron
is collected and measured as a current. If the metal surface is
contaminated, e.g., with grease, then the number of released photoelectron
is reduced by a quenching effect. Hence, by measuring the photoelectron
current, the extent of contamination on the metal surface can be
determined.
Ice
blast replaced the traditional process of cleaning and degreasing the
bonding metal surfaces in the manufacture of bimetallic tubing for the
nuclear fuel industry [5].
The figure below shows that the “As-Received” sample has a very low
OSEE value, consistent with the fact that it had machining oil and other
surface contamination. The “Conditioned” sample was scrubbed and
thoroughly cleaned with methyl alcohol to establish an OSEE value of 999
as calibration. Samples less clean will have lower OSEE values. One
Conditioned part was subsequently cleaned by the acid pickling process and
the other was ice blasted. The ice blasted sample has the same OSEE value
as the “Conditioned” sample, confirming that ice blast had the same
degreasing capability as methyl alcohol with scrubbing.
Figure
12: Comparative OSEE values.
In
nuclear decontamination, INEEL (Idaho National Engineering and
Environmental Laboratory) has evaluated both ice blast and dryice for the
removal of fixed contamination of Cs and Zr [6].
Table 1 shows the relative decontamination recorded.
|
|
Cs
(%) |
Zr
(%) |
|
Dry
Ice Blast |
63 |
78 |
|
Ice
Blast |
92 |
>98 |
Table
1: Ice / dry ice Decontamination Comparison
[5]
Herb, B., Visaisouk, S., 1996, Ice Blast Technology for Precision
Cleaning, Precision Cleaning ’96 Proceeding, Anaheim CA, pp. 172-179.
[6] Demmer, R., Janikowski, S., 2001, Evaluation of Two Commercial Decontamination Systems, INEEL/EXT-01-01013