in general the reusable parts of fuel are long lived and the parts that complicate reuse of spent fuel are short lived in general fuel becomes easier to reprocess over time largely because less shielding is needed to protect against radiation from the decay of short lived fission products one exception is the decay of pu with a half life of years to am half life years though the decay rate is much lower the radiation hazard is higher because the decay includes a low energy gamma ray recycled fuel with higher am is therefore somewhat harder to handle safely also the am is not fissile and is therefore prone to absorb neutrons in a standard light water reactor and produce higher transuranics rather than fission and produce energy and fission products so the spent fuel is also harder to handle fast reactors in principle can help reduce these problems since most transuranics undergo fission in a fast neutron spectrum but fast reactors do not have a strong track record of reliability and carry a significant cost premium so in considering the economics of recycling it's important to take into account not only the cost premium of the fuel but also the cost premium of the reactor needed to use the recycled fuel most effectively