that's exactly why they chose it and it makes a lot of sense.
If the environment is so stable, you don't have to worry about earth own internal movements too much.
This is old news, it's been amply debated, there's a documentary by Michael Madsen titled "Into Eternity" where pros and cons are discussed at lenght, the movie is from 2010, 13 years ago.
You can find it on YouTube
Reminds me of that Star Trek episode where Data, confused, walked with an suitcase with irradiated materials to a village that was just discovering the basic elements. They got irradiated because they couldn't understand the radiation symbols on the suitcase.
https://memory-alpha.fandom.com/wiki/Thine_Own_Self_(episode...
Right to me implies the best. Its not the best. Shooting it to the sun seems like a better alternative.
...may not be the correct decision.
Putting it deep underground is the safer option.
[1] you can use gravity assists like the Parker Solar Probe, or go very, very far out, make a small adjustment and then fall back in for about 1/3 the total delta-v.
To get something to fall into the sun rather than just carry on orbiting it you need it to lose the velocity it has by virtue of being launched from Earth, if you just punt it into interstellar space on the other hand you need a lot less fuel and you can get a boost from the planets if you line it up right.
"Space Launch Vehicle Reliability" - https://www.tech-insider.org/related/research/2001/0301.html
"Of the 4378 space launches conducted worldwide between 1957 and 1999, 390 launches failed (the success rate was 91.1 percent)"
This is the right solution - dry storage in hard rock in some rock formation that hasn't done anything in millions of years. Originally, in addition to Yucca Mountain, there was a plan for an East Coast nuclear waste repository in hard rock, probably in Maine or Vermont.
When it's full, the Finland plan is to fill in everything, seal it off, and not mark it. If some future society can drill through that much hard rock, they probably know about radiation, since that's a routine hazard in mining.