The presence of limestone<span> and other calcium carbonate rock in </span>lakes<span> and streams helps to maintain a constant pH </span>because<span> the minerals react with the excess </span>acid<span>. However, </span>acid rain<span> eventually can overcome the buffering capacity of the surface water.
The amount of uranium within nuclear fuel rods is enough to sustain a chain reaction but is less than the critical mass necessary for the reaction to become explosive.
