there is no real PI in national lab system. There are program managers and
personnel managers, they are normally not scientist, but decide who (a
scientist) can lead a project, when the project is done, the scientist can
join other's project, or lead another project. There are also internal
projects, called LDRD, which is 1-3 year term and internally reviewed.
Almost all scientists are supported by soft money, meaning you have to have
a project to charge your time, it is common that a national lab scientist
has to work on several projects, since the overhead is extremely high -
higher than what you can imagine :(