The helium nuclei a.k.a. alpha particles are also charged, like the free protons.
However, the alpha decay of some product of the fission reactions does not change the total charge of the fissile material, because the emission of a helium nucleus with a double positive elementary charge leaves a heavy nucleus with a diminished nuclear charge, by those two elementary charges.
Only when the alpha decay happens to occur close to the surface of the material, the positive helium nuclei may escape from it and they could land on a collecting electrode, making that electrode positively charged and leaving the fissile core negatively charged. However such a process would extract only a negligible part of the energy produced by fission. Even if the alpha extraction could be enhanced somehow, the decay energy of the fission products is small in comparison with the energy produced by the initial fission of the uranium nuclei. Extracting directly from the fissile material the nuclei generated by fission would be much more difficult than extracting the helium nuclei.
The Darpa project may succeed to stimulate the creation of some electric generators that could deliver additional energy from a fission reactor, by direct electric charge separation, but that would remain a small part of the total fission energy, most of which will still have to be extracted through thermal methods, like today.
However, the alpha decay of some product of the fission reactions does not change the total charge of the fissile material, because the emission of a helium nucleus with a double positive elementary charge leaves a heavy nucleus with a diminished nuclear charge, by those two elementary charges.
Only when the alpha decay happens to occur close to the surface of the material, the positive helium nuclei may escape from it and they could land on a collecting electrode, making that electrode positively charged and leaving the fissile core negatively charged. However such a process would extract only a negligible part of the energy produced by fission. Even if the alpha extraction could be enhanced somehow, the decay energy of the fission products is small in comparison with the energy produced by the initial fission of the uranium nuclei. Extracting directly from the fissile material the nuclei generated by fission would be much more difficult than extracting the helium nuclei.
The Darpa project may succeed to stimulate the creation of some electric generators that could deliver additional energy from a fission reactor, by direct electric charge separation, but that would remain a small part of the total fission energy, most of which will still have to be extracted through thermal methods, like today.