WASHINGTON, July 5 — A factory that makes uranium fuel for nuclear reactors had a spill so bad it kept the plant closed for seven months last year and became one of only three events in all of 2006 serious enough for the Nuclear Regulatory Commission to include in an annual report to Congress.

After an investigation, the commission changed the terms of the factory’s license and said the public had 20 days to request a hearing on the changes.

But no member of the public ever did. In fact, no member of the public could find out about the changes. The document describing them, including the notice of hearing rights for anyone who felt adversely affected, was stamped “official use only,” meaning that it was not publicly accessible.

“Official use only” is a category below “Secret.” Documents in that category are not technically classified but are kept from the public.