As I understand it, these devices take intensive upkeep to keep them usable. Even if they were in working order in 1998 (which is questionable) as I understand it there is just about 0 chance that they would produce more than a fizzle now, eight yrs. later. Does anybody know more about this?
Relevant points of a research story by the Center for Nonproliferation Studies:
First, the probability that any portable nuclear devices were lost prior to or after the breakup of the Soviet Union appears low; the scenarios of loss offered by the special commission in 1996 are actually the least plausible among other possible scenarios. This does not mean that the threat does not exist, but rather that at this moment, it is probably not the most immediate threat to the home security of the United States or to U.S. armed forces abroad.
Second, even if any devices were lost, their effectiveness should be very low or maybe even non-existent, especially if the loss occurred during the period of the greatest risk, in the early 1990s. Without scheduled maintenance, these devices apparently can produce only minimal yield and eventually possibly no yield at all, and can only serve as a source of small amounts of weapons-grade fissile materials.
Article available at:
http://cns.miis.edu/pubs/week/020923.htm