Reply #99: Agreed it is a generalization.

[Statistical]

However BWR can scram with no power also.

Usually the control rod assembly (which you are correct is below reactor vessel) can be fast SCRAMed by compressed air.

In a critical failure valves on compressed air tanks are blown and the control rods are forced at very high speed into reactor. Usually they are moved via slow hydraulics.

Personally I prefer PWR because control rods are held against gravity and thus is an any failure you are working with gravity not against it to slow/cool reactor.

Also didn't even get into neutron poison which is another passive safety. Compressed tanks of liquids with high neutron cross section are attached to reactor and sealed under extreme pressure. The seal is heat sensitive and melts at temperature higher than operating temp. If reactor overheats fast enough seals blow and reactor vessel is flooded with neutron poison which acts as a giant liquid control rods.

Add to that negative void coeficiency, passive cooling like on Gen III+ reactors (AP1000), redundant systems, and multiple power sources (grid, priority grid, onsite generators, offsite generators) and anyone researching reactors can see they are very redundant systems.