The AIAA is hosting a Space Nuclear Power & Propulsion Roundtable next week in Washington (there is some confusion whether the event is on Tuesday the 10th or Friday the 13th). The date, though, is a moot point for most: the roundtable is a closed session, open only to participants and other invited guests. The event will be taped for a future webcast. No reason was given for the closed nature of the event, although one possible reason is to shut out anti-nuclear protestors (think Bruce Gagnon and his ilk.) The list of roundtable participants is primarily from industry and policy circles, and it would appear that most would be in favor, to one degree or another, or nuclear power and propulsion applications in space.
Things like this are often closed for simple reasons–the size of the room and catering concerns, etc. If they’re providing lunch, they will want to keep the meeting small.
In addition, closed meetings theoretically allow people to be more open in discussing issues–people are reluctant to talk if members of the press or even the general public may be there. But I’ve seen even closed workshops where the government bureaucrats get nervous about saying even very unremarkable things. (And sometimes it’s fun to startle them by mentioning that their big secret appeared in the newspaper already.)