Until now no facility has been reprocessing spent nuclear fuels for rhodium and ruthenium; however Japan is planning to do so in their new spent fuel reprocessing facility, which will help offset the cost of reprocessing.
Each kilo of the fission products of 235U will contain 63.44 grams of ruthenium isotopes with halflives longer than a day. Since a typical used nuclear fuel contains about 3% fission products, one ton of used fuel will contain about 1.9 kg of ruthenium. The 103Ru and 106Ru will render the fission ruthenium very radioactive. If the fission occurs in an instant then the ruthenium thus formed will have an activity due to 103Ru of 109 TBq g-1 and 106Ru of 1.52 TBq g-1. Ru 103 has a half life of about 39 days meaning that within 390 days it will have effectively decayed to ground state, well before any reprocessing is likely to occur. Ru 106 has a half life of about 373 days meaning that if the fuel is left to cool for 5 years before reprocessing only about 3% of the original quantity will remain, the rest will have decayed to ground state.
It is also possible to extract rhodium from used nuclear fuel, which contains rhodium (1 kg of the fission products of 235U contain 13.3 grams of 103Rh. So as a typical used fuel is 3% fission products by weight it will contain about 400 grams of rhodium per ton of used fuel. The longest lived radioisotope of rhodium is 102mRh which has a half life of 2.9 years, while the ground state (102Rh)has a half life of 207 days.
Each kilo of fission rhodium will contain 6.62 ng of 102Rh and 3.68 ng of 102mRh. As 102Rh decays by beta decay to either 102Ru (80%) (some Positron emission will occur) or 102Pd (20%) (some gamma ray photons with about 500 keV are generated) and the excited state decays by beta decay (electron capture) to 102Ru (some gamma ray photons with about 1 MeV are generated). If the fission occurs in an instant then 13.3 grams of rhodium will contain 67.1 MBq (1.81 mCi) of 102Rh and 10.8 MBq (291 μCi) of 102mRh. As it is normal to allow used nuclear fuel to stand for about five years before reprocessing, much of this activity will decay away leaving 4.7 MBq of 102Rh and 5.0 MBq of 102mRh. If the rhodium metal was then left for 20 years after fission then the 13.3 grams of rhodium metal would contain 1.3 kBq of 102Rh and 500 kBq of 102mRh. At first glance the rhodium might be adding to the resource value of reprocessed fission waste, but the cost of the separation of the rhodium from the other metals needs to be considered.
These energy levels allow a more efficient neutron source than the Spallation Neutron Source.
Gold can currently be manufactured in a nuclear by irradiation either of platinum or mercury. Since platinum is more expensive than gold, platinum is economically unsuitable as a raw material. Only the mercury isotope Hg-196, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, and following K+-decay into Au-197 with slow neutrons. Other mercury isotopes are converted when irradiated with slow neutrons into one another or formed mercury isotopes, which beta decay into thallium. Using fast neutrons, the mercury isotope Hg-198, which is contained to 9.97% in natural mercury, can be converted by splitting off a neutron and becoming Hg-197, which then disintegrates to stable gold. This reaction, however, possesses a smaller activation cross-section and is feasible only with un-moderated reactors. It is also possible to eject several neutrons with very high energy into the other mercury isotopes in order to get the Hg-197. However such high-energy neutrons can be produced only by particle accelerators.
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