Joyo inlcudes the reactor containment vessel and reactor auxiliary buildings. The 54.3-meter tall reactor containment vessel is carbon steel with a 28-meter inner diameter and a 12~27mm wall thickness.It is a closed system, containing the reactor vessel and major components of the primary cooling system.
The reactor vessel is 10m high and made of stainless steel with a 3.6-meter inner diameter and a 25-mm wall thickness, and contains the reactor core – the heart of Joyo. It is equipped with a cover at the top of the reactor vessel which is a double rotating plug, by which refueling can be accomplished with safety.
The heat generated by the nuclear fission chain reaction of uranium and/or plutonium is transferred from the reactor core by means of sodium flow in the main heat transport system.
The main cooling building has four sets of main dump heat exchangers, which expell the heat generated in the reactor core to the atmosphere. Joyo is not equipped with a generator for electricity production.