Few are these...
1. Such country will gain higher position in international political scenario.
2. The country will gain access to nuclear technologies and can be able to sell its own technologies too.
3. The country can acquire nuclear minerals from other member countries.
4. Using nuclear technologies for power generation will reduce fossil fuel requirements.
5.finally, grouping is always profitable
But...the condition...these technologies, minerals can only be used for peaceful purposes like of energy production not for weapon development