"It's outside the environment."
> has considered a high-thrust nuclear
Of course we have. Always start at NTRS: https://ntrs.nasa.gov/citations/19690000736
> Certainly sci-fi has!
Our Solar system is a gravitational well that tends to put things in solar orbit. You really want the waste products to leave the solar system, which isn't terribly difficult, or you want them to land on the sun itself, which is exceptionally difficult.
Yes, it is counter intuitive but it takes less energy to leave the solar system get to the sun (you have to cancel out the Earth's orbital speed). Something learned from Kerbel Space Program.
In practice in the real solar system, the cheapest way to get from Earth to the Sun is to use Jupiter. Launch to there and reverse-slingshot to cancel out the orbital velocity and drop directly towards the Sun. The Parker Solar Probe would have done this, although decided not to because of the complications in designing to handle both the cold of Jupiter and the heat of the Sun.