Is "nuclear arsenal" different from saying just "nuclear weapon"?
"Arsenal" means a collection of weapons and military equipment. "Weapons" can be used in this sentence here with a similar effect, but it is less of a technical term. When someone is referring to the range of different weapons and equipment held by something or someone, "arsenal" is more commonly used than the simpler term "weapons." Thus, the speaker has chosen "arsenal" to indicate that the collection is diverse and contains different types of nuclear weapons. Ex: Russia has the biggest nuclear arsenal in the world. Ex: North Korea has been expanding its nuclear arsenal.