the amount of cesium that can be retained in the glass melter. So the quantity of cesium from the Hanford capsules, if any, that is needed for this process is not clear.
Is the half-life of the 137Cs long enough to permit the conclusion that the immobilization form meets the “spent fuel standard” if it is denatured with 137Cs instead of spent fuel?
The gamma radiation from spent fuel that has cooled more than 20 years is essentially all from decay of 137Cs (actually the 137mBa daughter). The second highest gamma source is 154Eu, which is only about 1 % of the 137Cs activity. All other significant radioactive isotopes are either alpha or beta sources. Therefore, the “spent fuel standard” really refers to 137Cs activity (after the first 20 to 30 years). The 137Cs activity (and the spent fuel standard activity) will decay away with a ˜30-year half-life.
Under what circumstances would it be necessary to add Cs, and how much Cs would be needed? Would sufficient Cs be available?
See the above discussion for the answers (and uncertainties) for the first part. The quantity of Cs required depends directly on the definition of the spent fuel standard. If the required gamma field is 1000 R/h at 1 m, we calculated that 20,000 Ci 137Cs would be required for each canister. The total activity of 137Cs available in the Hanford capsules is 54 MCi, so there is enough activity to protect about 2700 canisters. If the 50 MT plutonium were evenly divided among these 2700 canisters, there would be about 18.5 kg plutonium per canister.
The actual canister design, described in the above reference (L-20220-1), incorporates eight “ANL” canisters (9.0-in dia, 56.5-in tall) in a defense high-level waste (DHLW) canister. Each ANL canister would contain 6.5 kg Pu and 2500 Ci 137Cs, for a total of 52 kg Pu and 20,000 Ci 137Cs in the DHLW canister. Approximately 1000 such canisters will be needed to dispose of the 50 MT weapons-grade plutonium, so a total 137Cs activity of 20 MCi will be needed.
The gamma radiation from the spent fuel fission products could be used to reduce the number of cesium capsules needed, to reduce the amount of plutonium in each canister (by increasing the number of canisters), or to increase the gamma field around each canister. So, the answer to the question is: “Yes, there would be sufficient cesium available.”
If the proposed process is used ONLY for the EBR-II fuel, is there enough Cs to make the excess Pu meet the spent fuel standard?
The above discussion already answers this question. There is not enough activity in the spent fuel alone, in any case, but the radioactivity can be adequately supplied by use of the Cs from the Hanford capsules.
Are there specific impurities (such as fluoride ion) that could adversely affect the zeolite structure and behavior?
Other than large quantities of fluoride ion at high temperatures, we have not seen adverse effects of any material on the zeolite structure. We have looked extensively for effects of rare-earth, uranium, and plutonium ions, but have seen none. Because the amount of fluoride expected in the waste is essentially nil, we have deferred the determination of the allowable fluoride level.
Are there specific impurities that adversely affect the performance of the glass matrix?
We have not seen any such effects, nor have we identified any materials that might be expected to have an adverse effect at “impurity” levels. In the course of waste form fabrication, the glass