If your fuel is DEUT of PLUT, then you inject NEUT to react it. If your fuel is URAN, then you use some source of pressure to react it. You will need E-wall, stor or PCLN to control the NEUT, or you can have a laser that goes to INVS. Put a fast, strong heat conducting element connected from the core too a water tank. Put detector wall at the top, and connect that too output cable. After the detector wall your water vapour will need to be recycled into DSTW, so it can run again without the need to refill, or you can just make it go out into the air, and put CLNE inside. The WTRV can be circulated using PIPE, fan or portals, there are someother ways which use carefully placed force stuff. It will need to go down and under a tower known as the cooling tower. The cooling tower will need to be connected to a water source for when it loses all its water. One example is a river. when the WTRV has condensed, it should be recurculated into the main tank so it can be reused.