This is the 6371st most frequent Catalan word.
nuclear
"Related to the nucleus or central part of something; pertaining to nuclear energy or weapons."
In this context, 'nuclear' describes a type of energy derived from atomic reactions, used as an adjective.
L'energia nuclear és una font de poder molt debatuda.
Nuclear energy is a very debated power source.
Here, 'nuclear' metaphorically refers to the essential or central part of something, applied to family in this case.
El nucli familiar és considerat la unitat nuclear de la societat.
The family core is considered the nuclear unit of society.
In this usage, 'nuclear' pertains to the nucleus of an atom and indicates studies related to atomic structure or reactions.