This is the 2671st most frequent Russian word.
ядерного
"Ядерного" means "nuclear" in English.
The word "ядерного" is used as an adjective here to describe "weapons", indicating its relation to nuclear technology.
Мы изучаем воздействие ядерного оружия на окружающую среду.
We study the impact of nuclear weapons on the environment.
In this sentence, "ядерного" functions as an adjective modifying "энергетического сектора", specifying that it concerns nuclear energy.
Развитие ядерного энергетического сектора помогает экономике страны.
The development of the nuclear energy sector aids the country's economy.
Here, "ядерного" is an adjective describing "удара", denoting that the strike was from nuclear weaponry.