There's talk of moving low-level waste from Trawsfynydd out by rail. At some point the site will be flattened and they may wish to use rail to move the rubble, again to reduce lorry movements on local roads. Rolls-Royce are developing Small Modular Reactors and Traws has been mooted as a potential site, I'm not sure if those will ship out waste while in operation like full-size reactors do.
The problem with that would be the cost of rehabilitating the line beyond Blaenau. I remember looking at the accessible pounts of the line a decade or more ago, and it was getting pretty overgrown then. Unless someone has been doing some work since, I imagine there are bushes and even trees growing through the track by now.
IIRC the track was bullhead rail on timber sleepers, so it's likely to need complete relaying - it wouldn't be quite on the scale of East - West Rail, but there'll be similarities.
At a guess, it would need:
- Lift and scrap existing track
- Use road plant on the old ballast to cut and remove vegetation
- Rehabilitate drainage and culverts
- Remove old ballast to formation level
- Lay geotextile and fresh ballast
- Lay new track
It could presumably operate with one train in section, locked in at BF, so wouldn't need much signalling other than maybe for the level crossings.
Rebuilding the Leven line (double track and stations, but slightly shorter) was costed at £117m. Taking out stations, most signalling, and the second track, would still be likely to leave a cost of over £50m. Would the potential power station traffic ever justify that sort of expense?