Another Sodium Cooled Fast Nuclear Reactor Licensed in Russia.

[NNadir]

4. The Russians have built a series of reactors, particularly on submarines, that utilize LBE, lead bismuth eutectic.

The advantage of lead is that as a heavy metal it is self shielding. The concept has had some setbacks, materials science issues.

It is interesting that pure lead, a toxic metal, is transmuted into far less toxic bismuth in a neutron flux. In theory - although not to my knowledge in a practical sense - pure lead can generate it's own bismuth during operation. It's a way to get rid of lead, in theory, although the very high energy to mass ratio that makes nuclear energy environmentally superior to all other options, would make this effect small.