During reprocessing, what substance is used to dissolve spent nuclear fuel?

The use of concentrated nitric acid during the reprocessing of spent nuclear fuel is crucial due to its effectiveness in dissolving the complex mixture of metal oxides present in the fuel. Spent nuclear fuel primarily contains uranium, plutonium, and various fission products, which are predominantly in the form of metal oxides after irradiation.

Concentrated nitric acid facilitates the dissolution of these oxides, breaking them down into soluble nitrates. This process is essential for separating valuable fissile materials, such as uranium and plutonium, from the radioactive waste products. The use of nitric acid also allows for the formation of stable nitrate solutions, which can be further processed to extract and recycle these materials or manage the radioactive waste safely.

Other acids, such as hydrochloric acid or organic solvents like acetic acid, do not provide the same level of effectiveness for this particular application. Sodium hydroxide, being a strong base, is not suitable for dissolving spent fuel and would react differently, also leading to precipitation rather than dissolution of the target materials. Therefore, concentrated nitric acid is the preferred choice in this context due to its ability to efficiently dissolve spent nuclear fuel and enable subsequent separation processes.