I don’t find anything that shows a boron catch-pan component in this reactor. I do see they ordered up 52 tons of Boron and then later ordered 90 plus tons of Boron-10 from the French and they were mixing it with water and injecting it.
Boron-11 doesn’t do too much as Boron-10 has one less neutron and provides the perfect catch material for the excess neutrons slowing and cooling the reaction.
Of course, injection yields water vapor that is contaminated as it leaves.
Criticality (if it did occur) has long since been quenched by "dilution" of the corium with things like melted concrete, etc.
The largest source of heating was decay of short half-life fission products -- and they are long-since decayed.
Learning to read is highly recommended...