If I Google "diesel shelf life", the most common answer is 12 months. Do you have a better source? Propane probably makes more sense for fuel that needs to sit around for years.

Do you know the shelf life of TRISO fuel? I imagine it doesn't matter because it would be very expensive to build a reactor and not switch it on.

Diesel will degrade with exposure to oxygen, but a diesel engine can burn pretty much any flammable liquid that you can meter out. It really comes down to the engine itself and if it can handle less-than-perfect fuel.

Anecdotally, I came across a large (for a single user) quantity of diesel 9 years ago. (Nothing exotic - a company went titsup and I was the only one both bidding for and capable of removing the diesel from their premises within an acceptable time frame; I got approx 80% off the pump price at the time.)

I still run my tractor and Land Cruiser off the stuff; the tractor had an outing today. Granted, neither of those engines are very particular about the fuel they are given, but still...

(Water drained off every few months, also a biocide is added to keep the diesel gunk at bay.)

I mean if you trying to run that fuel in a performance application where you are pushing the fuel to its absolute limit, it might be bad, but most diesel engines can be run on nearly any burnable oil, you just get less power out and a bit dirtier burn.

They give similar specs ideals about gasoline fuel going bad in 3-6 months, and yet 95% of gasoline engines will still run 2 year old fuel fine because they aren't pushing compression ratios to the absolute possible limit, and half of the performance engines that do push limits these days have adaptable computer controlled compression and sensors which will figure out how much it can push the fuel.

If I put 5 year old diesel fuel into any regular diesel motor or generator or vehicle and it didn't start up, I would be extremely surprised, and be most worried that the fuel either wasn't diesel fuel to start with or had a wide open hole in the container that a bunch of rain water drained down into.

That said, if I had some kind of tuned up diesel motor that I was trying to push 800+ HP out of, I probably wouldn't use year old diesel fuel just in case. High performance motors like that are already straddling the line between working great and catastrophic failure and using old potentially bad fuel only adds to it.