The lower one is Hafnium, the blue one is Dark Pluto.
The word "Hafnium" should be on the side instead Hf-178m2, which is its power source though Induced Gamma Emission. Otherwise it is a closed circuit steam turbine electric, like most of the X-trains. Its IGE unit is the low slung grey cylinder in the middle.
It is one of the "X-Trains" found in Radio. Some of the others are Plutonium-238 Pilot, Sr-90, which are the same save for layout, weight, and heat source, and Dark Pluto.
Dark Pluto, being a NGTEL, is the odd one out. It is commonly seen with slugs (not the Slimy kind) in the rail yard. It was built with a modified version of the reactor found in the Pathfinder II orbiter (the people in Radio will stick a reactor in just about anything) to replace the Black Winds that were being used in the yard. The prime mover can develop 7500 horsepower. It has a top intake and top exhaust for the prime move and side intake and rear exhaust for the air cooled generator.
Hafnium and Dark Pluto are the heaviest of the X-Trains because of the shielding requirements.
Dark Pluto's prime mover.
This is Plutonium 238 Pilot. It was the first of the X-Trains and has had limited success. There are two large blocks of Pu238
on either end. It takes the two Isobreed (when I finish the RNEC, you will see them, but first I need a lot more RAM) reactors a month in two to three hour burns to generate enough of the hot metal to refuel it. With reactor cooldown times taken into account, it takes close to four months to make enough material. That said, it only needs refueling every 87 to 89 years.