This lab modeled nuclear waste disposal containment methods by sealing a pellet of sodium hydroxide, a caustic base, with (1) aluminum foil (2) plastic wrap and (3) modeling clay. Each of these "contained" pellets was softly dropped into a weak solution of phenolphthalein, an indicator. This “nuclear waste” was let sit under observation for three days.
After this three-day period, it was noted that the aluminum foil had degraded. To the effect that it had released a great quantity of “radiation”. This expressed itself with a change in the color of the indicator solution, from clear to dark purple. The clay did not change, save for a slight release of bubbles. The plastic was held closed with a piece of wire, which quickly rusted, turning the solution a light brown color. If an extrapolation is made, the wire would rust through, leading to a release of “radiation”.
This experiment was designed well. I found the experiment to be exemplary of the difficulty associated with containment. The use of an indicator solution to show leakage was an ingenuous way to visually express the idea of radiation.
1 comment:
In a similar lab that I ran, four small glass containers were filled with ~65-70 mL of water, and four drops of phenolphthalein were introduced. Approximately two ~5x6x1mm flakes of the sodium hydroxide were used in each. Upon placing the pellets into their respective containers, the sodium hydroxide almost immediately turned the water in the control a light shade of purple. The water in the jar with the plastic wrapped pellet started to change immediately, as did the aluminum foil water.
It was presumed that leak-through would not have occurred as quickly as it did, therefore it was further presumed that the sodium hydroxide had somehow gotten onto the exposed surfaces and these trace amounts were causing the color change. To remedy this, the solution was drained from the afflicted glass jars, they were refilled with the water phenolphthalein solution, and the same pellets replaced into them. The aluminum foil pellet contaminated the water almost immediately again. The plastic wrapped pellet did not recontaminate its water.
When observed on the second day, no change was found in the clay pellet. The wire used to hold the plastic wrap had rusted, and the aluminum had begun to decompose, darkening and the shade of purple in the water. Sedimentation began to occur in the jar with aluminum.
The sedimentation and coloring process continued in the aluminum foil water on the third day. No change was noted in the clay on this day, and rusting continued on the wire. The control's color intensity decreased.
It was determined that clay was the best container, because absolutely no leak-through had occurred. After that was the plastic, no leak through had occurred, but, as with Orion’s, the rusting seemed to indicate that the containment system may become unstable in the future. The worst container was the aluminum foil.
Post a Comment