This was a test site for Rocketdyne shuttle engines. In the hills between Los Angeles County & Ventura County, between Chatsworth & Simi Valley. Near Box Canyon.
I lived in So Calif for over 29 years.
I could see the glow from these tests, and on quiet nights, could also hear the roar, from my house in the SFV.
They were testing rocket ENGINES-—NOTHING nuclear. I know people who worked there. NEVER a word about anything nuclear.
The various propellants for rocket engines are pretty tricky, but NOT nuclear.
IF it is a Superfund site, it is because of the propellants being tested-—nothing nuclear.
The SSL1 reactor was an experimental sodium salt reactor in the ‘50s. It ran wild for two weeks if my recollection is correct. Sodium salt is a very difficult medium to use as a heat transfer medium, it is fluid at very high temps and the pumping system runs at the margins of technology.
If my memory is correct there were large releases of airborne radiation as the tried to put the genie back in the bottle.