The French language is quite logic and has a fairly efficient morphological system. For example, it can create nouns meaning 'the place where something takes place' using the forms -erie and -oir, and it often keeps the same 'root' in the nominal and adjectival form (fer/ferré).
Similarly, the adjectives royal and loyal have been derived from roi and loi respectively. It seems like French likes this form. But the noun noyau reverts back to the Latin root in the adjective nucléaire instead of noyal -e -aux. This seems odd, particularly as the masculine plural form would be identical to the plural of the noun.
And yet, compared to English, French has quite a tendency to chose French roots over Greek/Latin. Note the pairs éteindre/extinguish, presqu'île/peninsula or foyer/focus. I'm not saying noyal exists now, I'm asking if it conforms to the aesthetics and logic of the French language.