 If using a thorium fuel to produce fissile 233U, the SNF (Spent Nuclear Fuel) will have 233U, with a half-life of 159,200 years (unless this uranium is removed from the spent fuel by a chemical process).The presence of 233U will affect the long-term radioactive decay of the spent fuel.If compared with MOX fuel, the activity around one million years in the cycles with thorium will be higher due to the presence of the not fully decayed 233U.