It is possible for a fuel assembly to be critical at near zero power.

The reactor core holds up to 368 fuel assemblies, and 89 control rods.

Many of these are found in, and harvested from, spent nuclear fuel assemblies.

The power level is changed by manipulating control rods, which separate one fuel assembly from the next.

And in December 1970, a fuel assembly melted in another reactor.

If everything proceeds as planned, the first real fuel assemblies can be introduced to the reactor some time next year.

It conducts research and development of new alloys for fuel assemblies.

It contains 177 fuel assemblies, 48 of which are equipped with control elements.

If the fuel assemblies would fall, this could lead to re-criticality.

The heat generated in these attempts melted the fuel assembly.